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PAL Questions: 833 - Garden Tools: 346 - Recommended Websites: 680

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Keywords: Perennials--Care and maintenance, Vegetative propagation, Iris

PAL Question:

When is the best time to divide and transplant Irises? I have Japanese, bearded and yellow flag (I think) irises.

View Answer:

Rhizomatous irises (the kinds you have) are best divided in midsummer:

“Lift rhizomatous kinds, such as bearded iris, in midsummer and cut rhizomes into sections, each with roots and a fan of leaves; replant, with tops barely covered, 6 inches apart. Flowers will be sparse the next year, but good thereafter…”
(Source: American Horticultural Society Plant Propagation, ed. by A. Toogood, 1999, p. 202)

“The optimum time…..is six weeks after flowering. This is usually in midsummer, allowing time for the new rhizome to become established and make sufficient growth to produce fans to flower the following year. New roots that began growing immediately after flowering will then be strong enough to help anchor the new plants. Early spring is another suitable time, just as the other main period of root growth is about to start, but flowering may be forfeited, and if flowers are produced the stems will almost certainly need staking….Bearded iris cultivars are tough, and if the rhizome is large they can survive out of soil for many weeks. This is not an ideal situation, but it makes transport of the plants easy.”
(Source: The Gardener’s Guide to Growing Irises, by G. Stebbings, 1997, p. 93)

Good instructions can be found in these articles:
July, August Time to Divide Iris
Garden Experiences: Dividing Bearded Iris

Season Summer
Date 2008-01-10
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Keywords: Plant care, Hydrangea

PAL Question:

I am attempting to find detailed plant information on a variety of hydrangea called Hydrangea macrophylla 'Miss Belgium', and can find very little in my plant books and online. Do you have any suggestions? Some of the details I am looking for are flower shape and size, plant habit, height & spread, and foliage details.

View Answer:

I found some information about Hydrangea macrophylla 'Miss Belgium' in Glyn Church's book, Hydrangeas (Cassell, 1999):

An excellent pink in alkaline soil or in containers. The plant is ideally suited to pot and tub culture as it stays small and compact (3 ft.) and the rounded heads tend to be tiny, keeping the flowers in proportion to the bush. Its free-flowering habit and healthy nature are its good qualities. It is not the best plant for acid soils as the flowers will be a strident purple-blue.

There is a photograph of 'Miss Belgium' in Corinne Mallet's Hydrangeas: Species and Cultivars (vol .1).

Forest Farm Nursery website sells this variety, described as follows: "This delightful, compact shrub will fit the smaller garden to a 'T' and provide it with a long mid-season of rosy-crimson flowers. PSh/Med(not dry) acid:blue, alkaline:pink."

Season All Season
Date 2008-01-10
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Keywords: Malus domestica

PAL Question:

I would like to find a site that has a list of tip-bearing apple varieties. It does not have to be comprehensive. Many sites talk about them and mention only a couple.

View Answer:

A search of the North American Fruit Explorers discussion group sent me toward this information from the USDA Agricultural Information Service, as well as this list of 146 varieties.

According to Michael Phillips, author of "The Apple Grower" (Chelsea Green, 2005), most apples are spur-bearing or a combination of spur- and tip-bearing; only about 1% of all varieties are solely tip-bearers (such as Cortland and Russet).

Season All Season
Date 2012-03-03
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Keywords: Lavatera, Shrubs--Care and maintenance

PAL Question:

When and how do I prune my lavatera tree? We used to think this plant was a bush!

View Answer:

Lavatera does tend to grow vigorously, and can get quite woody. You can cut a third off the top of each stem in late autumn, and then in mid-spring finish your pruning by cutting all the previous year's growth to about 6 inches from the ground. Hard pruning will encourage flowering, and keep the plant more compact. New shoots may be slow to appear (may not happen until early summer).

In my experience, a small start of Lavatera turned into an 8 foot tree in one year, and because it was in a spot where a tree was not desirable, I took a cutting, then dug up the plant, and started afresh--but this may be an extreme solution to the problem!

Season All Season
Date 2006-02-11
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Keywords: Symphyotrichum, Perennials--Care and maintenance

PAL Question:

Can tall asters be sheared or lopped off, early in the growing season to control height and make them bushier? I have Aster novae-angliae 'Wild Romance'. I love the color and bloom-time, but would like them shorter.

View Answer:

Yes, asters (Symphyotrichum) can be pruned. This is sometimes referred to in England as "the Chelsea chop," and it is a technique that may be used for a number of different perennials, as this article by Bunny Guinness in the Telegraph describes. An excerpt appears here:

"Plants now commonly manicured by their snip happy owners are Campanula lactiflora, sedums, rudbeckias, echinaceas, asters and heleniums. These have their shoots chopped back by around a third in late May/June. The basic rule is that perennials which only flower once should not be chopped or you will lose the flowers; varieties such as peonies, irises and aquilegias."

Here is similar information previously available from the Colorado State University Cooperative Extension website:

"...control the height and shape of an aster by pruning. Gardeners can pinch asters like mums, regularly removing little bits of new growth until the first of July. However, an easier approach is to cut the aster back by one half in mid-June. At this time, the aster can be shaped. Outer stems can be cut lower than inner ones to produce a nice mounded plant. This shaping tends to encourage bloom near the base of the aster and discourage ugly brown stems. Although this pruning may sound extreme, it tends to delay flowering by only a few days and produces a much prettier plant."

Season Summer
Date 2008-01-10
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Keywords: Brassicaceae (Mustard/Cress family), Vegetables, Vegetables--Diseases and pests

PAL Question:

We have a couple of beautiful heads of cauliflower and a nice set of broccoli. The cauliflower looked nice until we cut through it to find lots of little bugs, turning some of the flower inside dark. We have a few aphids on our mustard greens, but the cauli bugs do not look like aphids.

Is it possible to grow ANY Cruciferae up here without infestations? I have NEVER been able to grow ANY type without some kind of bugs. At least the aphids wait until the bok choy flowers before they infest....and our yard has lots of ladybugs! Is there any hope?

View Answer:

We recommend that you start your seeds indoors to reduce the threat of insect infestation. Once the plants have begun to establish themselves, you can move them outdoors.

These books have great information about growing vegetables in the Pacific Northwest:

Growing Vegetables West of the Cascades: The Complete Guide to OrganicGgardening (by Steve Solomon, Sasquatch Books, 2007)
Sunset Western Garden Book of Edibles (Sunset, 2010)
Winter Gardening in the Maritime Northwest(by Binda Colebrook).

Colebrook explains that crucifers are "susceptible to attack by clubroot, cabbage loopers, imported cabbageworms, cabbage maggots, and gray aphids." Sunset recommends that to prevent pests, "plant in a different site each year. Row covers will protect plants from aphids, cabbage loopers, imported cabbage-worms, and cabbage root maggots. Collars made from paper cups or metal cans (with ends removed) deter cutworms, which chew off seedlings a the base."

Season All Season
Date 2008-01-10
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Keywords: Plant diseases--Control, Fungal diseases of plants, Paeonia, Plant diseases--Diagnosis

PAL Question:

I planted some peony bulbs last year and they grew nicely until they reached about 10 inches high. One was in the ground, and the other is planted in a medium sized pot outside. The one in the ground is now dead, and the other one is not looking good. It gets dark spots on the leaves, and then the leaves die. Can you help?

View Answer:

Without additional details, it is difficult to say what may be wrong with your peonies. The Penn State Extension has information on different diseases that can affect peony plants. What you describe sounds somewhat like peony leaf blotch or measles, as shown in Iowa State University's Plant Pathology webpage on peony diseases. Here is an excerpt:
"Peony leaf blotch is also known as measles or stem spot. Warm, humid weather provides optimal conditions for infection by the causal fungus, Cladosporium paeoniae.
The leaf spots are glossy and purplish-brown on the upper sides of leaves. On the lower sides, spots are chestnut-brown. Infection is generally more pronounced at the margins of outer leaves. Leaves may become slightly distorted as they continue growing.
Fungal infections on young stems first appear as elongated, reddish-brown streaks. As plant growth continues, infected tissue near the crown may darken and become depressed. Stems on the upper portion of the plant may show individual, raised spots. To manage peony leaf blotch, cut the stems at ground level in the fall or early spring. Rake the area before new shoots appear. Fungicides are available to help control the disease, but must be used in combination with other management practices. Also, providing good air circulation and avoiding wetting the leaves when watering can help reduce disease severity."

There are other possibilities, including peony blight, also known as Botrytis blight. The Royal Horticultural Society discusses this problem:
"Peonies collapse at soil level and the stem bases are covered in grey mould. In a severe attack the leaves are also affected and the plant may be killed or so badly weakened it fails to sprout again next spring. Infections also occur frequently behind the flower buds just before they open.
This is a disease that affects both herbaceous and tree peonies. It is caused by a fungus (Botrytis paeoniae) related to grey mould (Botrytis cinerea), which may also attack peonies in a similar way.
Wilt is encouraged by high humidity which builds up around dense clumps of peonies. Increase the circulation of air by thinning out overcrowded shoots. Also avoid over-feeding, especially with nitrogen-rich fertilisers, which encourages lush, disease-prone growth.
Cut out all infected stems well below soil level, as soon as you notice them. Don't put infected material in the compost bin but burn it or put it in the dustbin, preferably in a sealed bag. If whole plants are badly affected lift and destroy them in their entirety along with the soil surrounding the roots. This total destruction is essential as the fungus can produce black resting bodies (sclerotia), which survive for long periods in the soil ready to re-infect new peonies.
There are no fungicides available to amateur gardeners at present."

I recommend taking plant samples to your local county extension agent for diagnosis.

Season All Season
Date 2008-01-10
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Keywords: Plant diseases--Control, Fungicides, Powdery mildew diseases, Integrated pest management, Dahlia

PAL Question:

What can I do about powdery mildew on my dahlias? Should I throw the bulbs away, or does it only contaminate the plant above the ground? I have heard both too much water and not enough water cause this problem. Is either true?

View Answer:

The main thing you will need to do is destroy all the foliage affected by the mildew. The mildew can survive the winter on infected foliage, and then spread to new foliage.

Powdery mildew thrives where plants are crowded and there isn't enough air circulation, so give your plants space, a sunny site, and try watering in the morning, and watering from beneath the plants (not over the leaves) so they are able to dry off during the course of the day. As you indicated, too little water can also be a problem.

Here are two websites with additional information:
Univ. of California IPM Online Guide
OSU Extension Plant Disease Control

I did not come across any information specifically saying that powdery mildew will affect bulbs or tubers. I spoke to an experienced dahlia and begonia grower here who said that it should be all right to store and replant your tubers, as long as you thoroughly get rid of all the diseased foliage aboveground.

Colorado State University Cooperative Extension has some information about powdery mildew, including preventative measures and a recipe for making your own baking soda fungicide.

Season All Season
Date 2008-01-10
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Keywords: Weed control, Integrated pest management

PAL Question:

I have a smaller lawn, in a slightly shady area and have been having problems with dandelion and white clover. I don't mind a few weeds, but it is getting to be too many. Children and pets play on this lawn so I don't want to put anything that would be toxic to them on the lawn. What would you suggest I do?

View Answer:

We suggest, given that you are concerned for your children and pets, that you hand-weed your lawn. A little pocket knife is a great tool for doing this quickly and tidily. If you just spend a little bit of time at it a few days a week, it will go faster than you'd imagine. We recommend that you live with the clover; it is extremely difficult to eradicate.

Small dandelions are easier to pull out. The City of Seattle has excellent information about caring for lawns without pesticides, including hints about controlling dandelions. Look in the right-hand menu for additional links to lawn care information.

Here is a link to some information about a dandelion weeding tool. You can at least see what it looks like and how it works.

Season Spring
Date 2007-04-20
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Keywords: Native plants--Washington, Native plants--Care and maintenance

PAL Question:

Where can I buy plants native to the Pacific Northwest?

View Answer:

The Miller Library website has information on sources for native plants - see the section on finding northwest native plants.

Below is a list of nurseries close to Seattle:
1. MsK Rare Plant Nursery (and lots of NW natives) in Shoreline
2. Washington Native Plant Society plant sales and native plant and seed sources
3. Woods Creek Wholesale (and Retail) Nursery in Monroe, WA

And here is the Woods Creek Nursery's native plants list.

King County's Native Plant Guide has a list of sources, as does PlantNative.

Season All Season
Date 2008-01-10
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Keywords: Control of wildlife pests

PAL Question:

Wild rabbits invaded our garden area this year and ate 20 feet of bean plants and then ate all the leaves from my strawberry plants. What can I do next year to discourage the little creatures?

View Answer:

We have looked at several resources, and there are several options for keeping rabbits away from your plants.

1. Exclusion fencing: You can use chain link, rabbit wire, 1-inch chicken wire, hardware cloth, or similar materials. The fence need only be 2 to 3 feet tall, but rabbits are great at digging under things, so the bottom of the fence material should be secured by staking it or burying it 8-10 inches deep. You can also make a hardware cloth skirt for the bottom of your fence, extending out on top of the ground about 2 feet. Secure it with stakes or garden staples, and then cover it with soil, mulch, or gravel. Make sure your gate areas are also secure.

You might try planting in raised beds which will discourage, if not totally stop, the rabbit visitors. Cages made with chicken wire and rebar can be placed over the raised beds. Chicken wire placed in the bottom of the raised bed or planter will keep rabbits from burrowing and tunneling from below.

One source recommends using electrified wire 4-6 inches from the bottom of an existing fence, but this requires a consistent power source, and cannot be touching any vegetation or it will short out. Some urban areas do not allow the use of hot wires.

2. Provide an easier food source for the rabbits, such as sunflowers, or cracked corn, outside your fenced/protected garden area.

3. Use pepper spray (this is available in garden centers or you can make it at home) on your plants. The spray is diluted in water and applied to the plants (about 1 tablespoon per gallon of water).

4. Install motion-activated noisemakers, such as croaking frog statues, and the sound might scare away the rabbits.

5. Live-trapping (used in combination with exclusion fence): "have-a-heart" traps are available in garden centers, and can be placed in sheltered areas (so rabbits won't have to cross large open spaces to reach them). Bait the traps with apples, carrots, cabbage, or other green vegetables (or better yet, use whatever the rabbits have been munching on in your garden!). The rabbits should be released away from urban areas.

Season All Season
Date 2006-02-11
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Keywords: Continuing education, Horticultural therapy

PAL Question:

Do any colleges or universities in the Seattle area have programs on horticultural therapy?

View Answer:

At one time, Edmonds Community College offered a certificate in therapeutic horticulture but they do not any longer. You can find other programs available around the U.S. on the website of the American Horticultural Therapy Association.

The University of Washington doesn't offer a horticultural therapy program, though there may be individual courses through the department of Landscape Architecture. Professor Daniel Winterbottom specializes in "ecological urban design and the role of restorative/healing landscapes in the built environment." The Miller Library has a good selection of books and articles on the horticultural therapy, including information about making raised beds, appropriate tools, gardening for the differently abled, and the like. This booklist will give you an idea of the resources available. For information about library hours and directions, go here.

Season All Season
Date 2008-01-10
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Keywords: Crassula, Insect pests--Identification, Insect pests--Control, House plants

PAL Question:

My 100-year-old Jade plant is about 5 feet tall and recently has been producing a sap from its leaves. White and sticky. Is there anything I can do to help this? Is it normal? Or is it endangering the plant? It is in kind of a cool spot; should I move it to a warmer place? It is a succulent, right? I would also like some information about repotting if necessary.

View Answer:

The pests most likely to cause a white, sticky substance are aphids, whiteflies, scale or mealybugs. These are known to affect jade plant, or Crassula ovata, which is indeed a succulent. They won't destroy plants, but can weaken them and allow other problems to surface. If none of the pest descriptions below resemble what you are observing, you can take affected plant samples to a local county extension agent. Without knowing the specific pest, we can't suggest specific treatments. Northwest Center for Alternatives to Pesticides provides general information on caring for houseplants. Note their description of mealybugs, which do produce a sticky substance:
"These insects look like little bits of cotton that are greasy or waxy. They are oval in shape, have a segmented body, and are about 1/4 inch long. You'll usually find them hidden between leaves and stems or under leaves. They move slowly. They make a sticky liquid called honeydew and also cause leaves to become distorted and spotted."

As for temperature and repotting, The New House Plant Expert (by D. Hessayon, 1991, p. 212), says that succulents like a difference between day and nighttime temperatures. They like to be kept cool in the winter, with 50-55 degrees F ideal, but as low as 40 is alright. Jade plants should only be repotted when essential. Repotting should occur in the spring; shallow pots rather than deep ones are preferable.

Extensive care information can be found on Succulent-plant.com. There is also excellent general information on indoor care of succulents and cacti from Brooklyn Botanic Garden.

Season All Season
Date 2006-12-08
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Keywords: Sustainable architecture, Irrigation water quality, Water reuse, Water conservation

PAL Question:

I need to replace my roof, and I am thinking of installing asphalt or composite shingles because they're what I can afford. I planned to capture rain water to irrigate my vegetable garden, but I'm concerned about toxicity. Is runoff from the shingled roof likely to be toxic?

View Answer:

I would not recommend using reclaimed rainwater from an asphalt shingle roof for any edible crop. Asphalt is petroleum-based. The runoff might be acceptable for ornamental plants, but the fact that asphalt or composite shingles tend to shed tiny particles means that those particles would be introduced to the soil around your crops.

An article from North Carolina State University Extension discusses "Water Quality of Rooftop Runoff." It doesn't specifically mention asphalt, but I don't think it would be wise to use the reclaimed water on food crops.

Green Living Journal has an article about roofing materials,and discusses asphalt shingles as well as alternatives.

The National Gardening Association site has a report that describes rainwater harvesting.
Excerpt:
"Water from the rain barrel is, of course, not potable, but some experts also raise concern about possible contaminants from rooftops that can make the water unsuitable for edible gardens. According to an article in Landscape Architecture magazine, asphalt shingles and other porous or rough roofing materials can hold particulates such as bird droppings and other debris, as well as heavy metals from the air, which then wash into the rain barrel. Wood shingles that are chemically treated to resist rot and algae can leach the chemicals into the rainwater running off the roof. Zinc strips that prevent moss build-up can also be problematic. Some large-scale rainwater collection systems are even designed to allow for the first flush of water off the roof -- which carries the majority of the questionable substances -- to be diverted.
Other people dispute these risks and say washing your garden produce is all that's needed. It's a judgment call. I tend to research things to death so I think it would be interesting to have some of my rooftop runoff tested at the health department."

If installing slate, clay tiles, untreated wood shingles, or a green roof is prohibitively expensive, the best solution might be to landscape the garden in such a way that you can reclaim runoff from the roof for non-edible plants.

Season All Season
Date 2010-01-08
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Keywords: Euonymus, Osmanthus, Ilex, Hedges

PAL Question:

Can you all give me some recommendations for plants that will form a tight hedge? I want a fast growing plant that does not get more than 2-3 feet tall and 2-3 feet wide. I do not want boxwood. Evergreen with glossy leaves is preferable; flowers do not matter to me.

View Answer:

I collected some information from websites and a couple of books for you. I am making one other plant suggestion, and it is the last item.

Euonymus japonicus 'Microphyllus'
Text
Images

Ilex crenata 'Northern Beauty' is described on the website of Great Plant Picks

Ilex glabra 'Shamrock'
See Missouri Botanical Garden for information and an image.

Osmanthus delavayi
This can be grown as a dense hedge. It can reach about 8 feet, but takes pruning well. Evergreen and attractive all year. Small, oval, tooth-edged leaves. Fragrant tiny white flowers in spring. Here in Seattle it can take the full sun but partial shade is okay too.

See the following website for both information and an image. Great Plant Picks is a local organization with information about plants that do particularly well in the Pacific Northwest.

Season All Season
Date 2006-12-08
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Keywords: Plant nutrients, Citrus limon, Potted plants, Water requirements, Fruit--Care and maintenance

PAL Question:

I purchased a small Meyer lemon plant from a nursery in Florence, OR, and it grew, and blossomed very well, and even produced many tiny lemons - all of which have now, at this point, dropped off. The leaves are yellowing, too. It is in a good size container, in full sun. The container sits in a large saucer which does fill with rainwater. This I empty, but the plant remains wet. New blooms are coming on some of the branches, old blooms are shrivelling. No more lemons coming as yet.

My question is, why did the tiny lemons drop off? And, should the plant get overly wet? My nursery person has no information. I would appreciate any information you have.

View Answer:

The following information comes from Citrus (by Lance Walheim, Ironwood Press, 1996).

It sounds as if your container has good drainage, but maybe the plant is getting too much rainwater. That might be causing the leaves to turn yellow. Another cause could be a nitrogen deficiency, which would be most visible in older leaves, which would yellow from the tip to the base.

As far as the plant's water needs, it will need water when the top two to three inches of soil become dry. Frequent watering (or excess rainwater) can leach nutrients from the soil, so the plant will need to be fertilized regularly -- once or twice a month using a liquid, high-nitrogen fertilizer that includes the micronutrients zinc, iron, and manganese.

The small lemons which drop off may not be anything to worry about, as fruit drop occurs normally as the tree varies its fruit load with its carrying capacity. Pea-sized fruit usually drop about one month after bloom. A more noticeable drop occurs in late spring to early summer, when golfball-sized fruit may drop. Other reasons for fruit drop could be conditions which limit tree growth, such as excess heat, lack of soil moisture (not relevant in your case), and fluctuating weather conditions. It is also possible that the fruit drop is due to lack of nitrogen.

Season All Season
Date 2006-03-06
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Keywords: Nurseries

PAL Question:

Is there a print or online resource for locating plants (places where they are sold)?

View Answer:

You can search the Andersen Horticultural Library's Plant Information Online. But be aware that they only include a selection of nurseries (those who post their inventory online). Most local nurseries are not included, as their inventory changes too frequently. You can also search using your favorite search engine for the name of the plant you are seeking plus the word nursery. This will not give you any clues, however, as to the reputation of the nurseries which show up in your search results. The website of Dave's Garden does have a forum of nursery reviews (called Garden Watchdog) you can consult.

Season All Season
Date 2007-09-21
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Keywords: Acer palmatum, Tree planting, Transplanting

PAL Question:

I would like to transplant a Japanese maple, probably 5 years old and about 8 feet tall. Can I do it in late October/November safely in St. Louis? And what is the best method?

View Answer:

Japanese maples are best transplanted when they are dormant---usually late fall through early spring if the ground does not freeze in your area.

The following information comes from Japanese Maples (by J.D. Vertrees, 2001, pp.61-62). This book also contains good information about mulching and general care:

When moving a plant to a different location within a garden, the plant must be dug with an earthen ball intact around the roots. If the plant is of any size or age, this root protection is important. It is also desirable that the planting hole be prepared in advance, ready to receive the plant with its root ball, as soon as it is dug up. Having the new planting hole ready minimizes the risk of the fine feeding roots drying out. For this reason it is imperative that, whatever method, material, or timing is used when planting a Japanese maple, the roots are not exposed to air or direct sunlight for any length of time. Such care will help prevent them from becoming desiccated, which would cause too much transplant shock and possible loss of the tree.

The planting hole should be dug slightly larger than the root mass of the plant. To enable the root system to establish itself quickly, it helps to mix with the soil organic compost, such as composted conifer bark mulch, rhododendron or azalea planting mix, or rose compost. In tight , heavy clay soils the compost helps condition the soil, while in light, sandy soils the compost assists in water retention. Sawdust or wood chippings should never be used as, during their breakdown, they use up the available soil nitrogen and render it unavailable to the newly planted tree.

The planting hole should be deep enough so that the root collar of the plant, the ground line at which the young plant was grown, is level with the ground surface. The exception to this rule applies to tight, heavy soils, like clay, where success will be greater if the hole is rather shallow so that the root system is partly above the ground level. When filling in the hole, the soil should then be mounded up to the root collar to protect the roots from drying out. If deep holes are dug in heavy soil, it is like planting the tree in a large iron kettle with no drainage. Surely the plant will soon drown and die.

Whatever the soil conditions, the tree should never be planted deeper than the root collar. After the first season or two, the plant will find the level of root activity at which it can exist in particular soil conditions. I have observed maples growing in some surprisingly dry, shallow, and exposed conditions.

Season All Season
Date 2006-11-14
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Keywords: Trees--Diseases and pests--Washington, Pinus, Master gardeners

PAL Question:

Recently we noticed that one of our evergreen trees has a lot of needles that are turning yellowish brown and dropping off. I would say about 25% of the needles are affected, some in the middle of the branches, some at the ends. The needles are about 3 - 1/2 inches long and are in bunches of five - I think it is a pine.

Is this normal for that type of tree? Or is it more likely the tree is stressed for some reason and we need to deal with it?

View Answer:

This will be a lengthy answer and I will assume you live in the Pacific Northwest---the following information will not apply to other areas.

In order to get an accurate diagnosis you will need to take a sample of your plant (including both healthy and affected parts if possible) to a Master Gardener clinic.

Meanwhile, to learn about diseases common to pines in the Pacific Northwest, go to the Pacific Northwest Plant Disease Management Handbook and search using the term pine.
There are several possibilities with good photos. Remedies are included with each disease.

Insect information is more difficult to get, so following are the most likely-sounding pests:

1. Pine (Pinus) - Black pineleaf scale (Nuculaspis californica)

Pest description and crop damage
Mature scales are almost circular, 1/16 inch in diameter, and yellowish brown to black. Young hatch in spring and summer. Scale feeding is restricted to the needles and results in their becoming splotched with yellow patches. Heavy infestations cause premature needle drop and may result in death of the tree. Affected trees often display a thin crown, yellow or reddish coloration, and a shortening of the needles. This insect attacks various species of pine, ponderosa most commonly, as well as Douglas-fir and hemlock.

Biology and life history
This scale overwinters as an immature. The crawlers start to disperse to fresh foliage in spring. There may be one to three generations per year.

Management-cultural control
Trees under stress tend to be particularly susceptible to attack, as are trees growing in dusty conditions. Avoid creating these types of conditions.

Management-chemical control (home)
Dormant season:
Apply with enough water to cover the entire tree thoroughly.
1. horticultural oil. Apply during delayed-dormant period.
Growing season:
insecticidal soap

2. Pine (Pinus) - Eriophyid mites (Trisetacus spp.)

Pest description and crop damage
Eriophyid mites are tiny, wormlike, whitish or tan mites which feed under bud scales or in the needle sheaths, often between the needle bases. Symptoms of eriophyid mite infestations include yellowing, distortion, and stunting of new needles, and development of numerous buds where a bud has been infested (rosetting). Severe infestations may kill needles and cause needle drop, leaving naked branch tips. Rosettes may develop into witches' broom growths. Two-needle pines, particularly lodgepole or shore pine, are affected.

Management-cultural control
Prune out heavily infested growths.

3. Pine (Pinus) - European pine shoot moth (Rhyacionia buoliana)

Pest description and crop damage
Adult moths are reddish-orange with silver markings on the wings. The mature larvae are about 5/8 inch long and reddish-brown with black heads. The larvae of the European pine shoot moth feed on tips of branches, boring first into needles or bud bases, then into the shoots. Infested tips are covered with pitch-covered webbing, often develop a characteristic "shepherd's crook" shape, and may die back. Infested needles are yellowed near the twig tips and eventually turn brown and die. All pines are susceptible, especially two- and three-needle species.

Biology and life history
The insect overwinters as larvae in the mined buds, covered with resin-coated webs. The adult moth lays eggs on new shoots near leaf bases in the late spring. The larvae hatch and bore into the needles, which turn brown by summer. By midsummer, they are mining in the buds and cease feeding by August. There is one generation per year.

Sampling and thresholds: Check for yellowed leaves at shoot tips in midsummer.

Management-cultural control
Prune and destroy infested tips in spring, before adults emerge. Be sure to prune far enough down the branch to remove the insects.

Management-chemical control (home)
1. azadirachtin (neem extract)

Season All Season
Date 2008-01-10
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Keywords: Abies, Plant diseases--Diagnosis, Trees--Diseases and pests

PAL Question:

Can I attempt to diagnose a diseased tree online? We're getting more brown spots on our grand fir and I would like to try to figure out what is wrong.

View Answer:

You can attempt it, but you will not know for certain based solely on a comparison of symptoms. You can certainly get an idea of what the potential problems could be. Try the Pacific Northwest Disease Management Handbook online---it has excellent photos. Search for fir.

There are several possibilities with brown spots as symptoms, especially:
*needle casts (there are 3 kinds)
*rust
*web blight
*current season needle necrosis
*shoot blight
*Grovesillea canker
*interior needle blight

The best way to diagnose a problem is to bring photos of the affected tree along with samples (if you can reach them) to your local county extension agent or Master Gardener diagnostic clinic.

Season All Season
Date 2008-01-10
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Keywords: Tree protection, Arbutus menziesii

PAL Question:

Are madrona trees protected within the Seattle city limits?

View Answer:

The City of Seattle, together with Plant Amnesty, maintains a Heritage Tree Program to protect notable specimens (notable for size, form, rarity, historical import), and there is also information from the city about tree protection regulations in Seattle. Madrona, a native tree, is designated as sometimes being considered exceptional (i.e., deserving protection) Click on Tree Protection Regulations (Seattle Municipal Code, Ch.25.11) in the right hand menu. Click on Director's Rule 6-2001 for a specific mention of madrones (Arctostaphylos menziesii: exceptional trees, p.4). Here is an excerpt:
"Healthy young specimens of Madronas on construction sites are more worth saving than old, large ones. As many specimens as possible in very good condition—regardless of size—should be preserved on construction sites, but they should not be watered or they will be more likely to decline and die. Large specimens of average or poor health may have a short lifespan because of damage during construction and as a result of post-construction practices such as irrigation—harmful to this species."

Season All Season
Date 2008-01-10
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Keywords: Berberis, Vaccinium ovatum, Polystichum munitum, Amelanchier, Acer circinatum, Soil stabilization, Soil erosion, Slopes (Soil mechanics), Corylus, Alnus, Philadelphus lewisii

PAL Question:

Can I plant groundcovers, shrubs, and trees to stabilize a steep slope?

View Answer:

There are several resources which will help you in selecting plants to prevent erosion and mudslides on your slope.

Please note that these articles are merely suggestions and should not be construed as advice. We are librarians, not engineers!

None of our standard books on trees mentions the soil binding quality of tree roots. However, the Miller Library does have very good technical books and articles on slope stabilization. (For example, Slope Stabilization and Erosion Control: A Bioengineering Approach, edited by R.P.C. Morgan and R.J. Rickson, 1995.)

I do want to note one thing that many articles mention: no amount of established vegetation will hold a steep slope if other forces are present that would contribute to a landslide.

The Department of Ecology website has a list of appropriate plants.

Additionally, there are a number of books with information on the subject. Vegetative Contribution to Slope Stability at Magnolia Park (by Kathy Parker, 1996) recommends Oregon grape (Mahonia), which she suggests for gentle slopes.

Other smaller plants she lists are:
Polystichum munitum (native sword fern)
Vaccinium ovatum (evergreen huckleberry)
Symphoricarpos albus (snowberry)

Larger shrubs in her list:
Alnus rubra (red alder)
Philadelphus lewisii (mock orange)
Sambucus racemosa (red elderberry)

Small trees:
Acer circinatum (vine maple)
Amelanchier alnifolia (serviceberry)
Corylus cornuta (hazelnut)

For steeper slopes, Parker says that they may not be good candidates for vegetative rehabilitation unless you put in some kind of structure. She says that Jute mats can be used in conjunction with native seed, mulch, and shrubs, if carefully anchored. She also mentions a Weyerhaeuser product called Soil Guard.

Steep Slope Stabilization Using Woody Vegetation (by Leslie Hennelly, 1994) has a plant list, as well as a chart which indicates plants used to control erosion, the degree of the slopes, and the rate of success in resisting erosion.

Two titles which focus more on the garden design aspect of planting on a slope are Hillside Gardening : Evaluating the Site, Designing Views, Planting Slopes (by William Lake Douglas, 1987) and Hillside Landscaping (by Susan Lang and the editors of Sunset Books, 2002).

Season All Season
Date 2008-01-10
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Keywords: Plant care, Leycesteria

PAL Question:

I am trying to find the proper soil pH for growing Leycesteria 'Red Shuttle'. I am hoping to plant it in partial shade next to rhododendrons (acidic soil). How will it do?

View Answer:

Leycesteria 'Red Shuttle' is the formosa species and should do well in any fertile soil, provided it is not highly alkaline (according to The Plant Care Manual by Stefan Buczacki (Crown Publishers, 1993).

Plants That Merit Attention, Vol. 2, Shrubs , (by the Garden Club of America, 1984, p. 172) states:

Needs sun for best bract and fruit color; prefers rich, moist loam; tolerates wind, drought, and air pollution...A handsome woodland shrub best in natural setting or shrub border. Needs sun for best flower and fruit color. May be pruned in spring. Partial dieback in winter not unusual; shrub rejuvenates the following growing season, often growing back successfully from roots....

Trees and Shrubs for Pacific Northwest Gardens (by J. Grant, 1990, p. 239) states:

...This shrub is easily grown in any good garden soil in full sun but prefers a rich, moist loam. It may achieve a height of as much as 15 ft. in a sheltered position. The rootstock is perfectly hardy, but the top is occasionally cut to the ground in exceptionally severe winters. If pruned almost to the ground every year, which is one method of treatment, it will send up lusty 6-ft. shoots and flower freely during the latter part of the summer....

Season All Season
Date 2006-03-04
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Keywords: Mealybugs, Scale insects, Insecticidal soap, Crassula, Insect pests--Control, House plants

PAL Question:

I have been nursing a Jade plant cutting that dropped off an overwatered and rotting larger plant. It has been thriving in my windowsill for 6 months or so, and has grown a lot already.

In the last week or so, I have noticed a strange white speckling on the upper surface of almost all of its leaves. Upon close inspection, it does not look like insects; it looks sort of like a detergent residue, and if I scrape my nail against the surface of the leaf, a lot of it will come off, albeit with effort.

Do you know whether this is something I need to treat?

View Answer:

I wouldn't assume the spots are a problem. As the following link to North Dakota State University Extension mentions, it might be salt crystals that you are seeing:
"Those dots are salt crystals and can be wiped off with a damp cloth or just ignored because they are not causing any harm to the plant. All water (except distilled) contains some salt. When fertilizer is added to the root system, the plant takes up the nutrient salts with the water. As the water moves through the leaf pores during transpiration, the salts often are left behind on the surface."

However, if you were to use a hand lens (not just the naked eye) and discover insects, there are resources with information on identifying and treating insect problems on indoor plants.

1. http://www.succulent-plant.com/pests.html

2. Washington State University's PestSense site lists several common houseplant pests, with information about treatment.

Always test any spray on one leaf before spraying the entire plant.Wait a few days after the test spray. Some plants are more sensitive to various soaps or oils.

3. The Northwest Center for Alternatives to Pesticides also has a guide to Growing Houseplants without Using Pesticides.

Season All Season
Date 2008-01-10
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Keywords: Pumpkin, Seed storage

PAL Question:

I have some white pumpkins and I want to save the seeds and plant them next year. What should I do?

View Answer:

There are several varieties of white pumpkins, the most common being Cucurbita maxima 'Lumina.'

Quoting from The American Horticultural Society's Plant Propagation (ed. by A. Toogood, 1999, p. 300):
Leave ripe pumpkins for at least three weeks in a sunny, airy place at about 70 F to allow the seeds to mature. When the pumpkin starts to soften, cut it in half and flick out the seeds with a knife. If needed, wash off any flesh, then dry on paper towels before storing....The seeds remain viable for 5--10 years.

And quoting from Seed to Seed (by S. Ashworth, 2002, p. 29):
Home-saved seeds will retain maximum vigor when thoroughly dried and stored in a moisture-proof container...The two greatest enemies of stored seeds are high temperature and high moisture. Seeds that are stored at fluctuating temperature and moisture levels will quickly lose their ability to germinate...

Season Fall
Date 2006-02-25
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Keywords: Climatic zones, Magnolia

PAL Question:

Will the evergreen magnolia, Michelia wilsonii, grow in Danville, CA?

View Answer:

It is suitable for your area in Danville (according to the Sunset Western Garden Book). As far as surviving the full sun in your hottest summers, you might want to check with a local nursery about that to be quite sure. The Sunset book says it needs partial shade in the hottest climates [that it grows in], and your Sunset zone appears to be 9, which suggests it has high summer temperatures. It may need to be planted where it will get partial shade.

Season All Season
Date 2006-02-27
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Keywords: Weed control, Mulching

PAL Question:

What is the best time of year to use Casoron and/or Preen for weed control on ornamental beds?

View Answer:

Both of these herbicides are registered pesticides, and the law requires that they be used in strict accordance with the directions (and only on the weeds/pests for which they are registered). It is safer for you and the environment if you manage weed problems without the use of pesticides.

You may wish to know more about these particular pesticides. Both Casoron and Preen are pre-emergents, meaning that they work to kill seedlings before they sprout. This means they will not eliminate weeds that have already broken through the soil surface and are growing above ground.

Casoron is persistent in both soil and water (i.e., it hangs around). Its active ingredient is dichlobenil. There are numerous environmental and health concerns associated with this chemical. Dichlobenil will kill any plants which are exposed to it, and will harm beneficial soil microorganisms. Below is a fact sheet about dichlobenil from Northwest Coalition for Alternatives to Pesticides.

The active ingredient in Preen is trifluralin. It is a suspected carcinogen, and is toxic to fish and aquatic life, and earthworms. Here is more information from Cornell University and Pesticide Action Network UK.

The links below provide information about alternatives to chemicals for weed control. Northwest Coalition for Alternatives to Pesticides has a page of factsheets about specific weeds and ways to manage them. Here is their page on managing weeds in garden beds.

Washington Toxics Coalition also has information on ways to handle weeds in the garden. Here is more information in a PDF file.

Before reaching for chemical weed control, it makes sense to adopt gardening practices which will help keep the weed population low. Mulch is an excellent way to control garden weeds. After you manually remove weeds from an area of your garden, apply a layer of mulch. This should suppress weed growth and help retain soil moisture. Here is what garden expert Cass Turnbull says about mulch:

Not only does mulch retain water, smother tiny weeds and weed seeds, and make it easy to pull new weeds, it is also harder for new wind-borne weed seeds to get a foothold.

Mulch can be spread anywhere from 1 inch to 4 inches thick. The thicker it is, the more effective and longer lasting. Spread it thick in big empty spaces. Spread it thin around the root zones of shrubs to allow for sufficient air exchange, especially around shallow-rooted plants like azaleas and rhododendrons. And never let mulch stay mounded up in the base or the "crown" of a plant. It can cause crown rot on some shrubs and can kill them, even a year or more later.

Source: The Complete Guide to Landscape Design, Renovation, and Maintenance, Betterway Publications,1991.

Season All Season
Date 2008-01-12
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Keywords: Plant litter, Plant physiology, Magnolia

PAL Question:

I have noticed that Magnolia leaves seem to decompose more slowly than other leaves...can you tell me why that might be the case?

View Answer:

There is a lot of anecdotal evidence regarding your observation. Finding information to specifically confirm it is not easy, however. But some facts about plants physiology help, especially in combination with considerations about the conditions required for decay. I referred to Introduction to Plant Physiology (William G. Hopkins, 1995) for most of the information below.

Lignin is a compound that is an integral part of the cell walls of plants. (It is the second most abundant organic compound on earth after cellulose.) Lignin fills the spaces in the cell walls of various plant tissues, providing mechanical strength to the cell wall and thus to the entire plant.

Lots of lignin in a leaf would result in a slow process of decomposition because it is difficult to degrade. That is, it is not easy for bacteria and water (necessary for decomposition) to penetrate the chemical structure of lignin.

Suberin is a waxy substance that is highly hydrophobic (repels water); its main function is to prevent water from penetrating plant tissue. Suberin is found in the outermost layer of the bark (in the dead corky tissue). The cells in this layer are dead and abundant in suberin, preventing water loss from the tissues below. Suberin can also be found in various other plant structures, including leaves, where it also prevents the movement of water.

So, the combination of a structural function of lignin and the water-repelling characteristics of suberin - in leaves, in this case - is quite helpful in explaining why magnolia leaves decay at a slower rate than other leaves.

An article about composting from University of Florida Extension mentions that magnolia leaves would need to be shredded in order to be usable in compost (or as mulch).

Season All Season
Date 2008-01-10
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Keywords: Kolkwitzia amabilis, Woody plant propagation

PAL Question:

How do I propagate Kolkwitzia amabilis?

View Answer:

There are a couple of methods of propagating Kolkwitzia amabilis. Fine Gardening says to take greenwood cuttings in late spring or early summer, or remove suckers in spring.

The American Horticultural Society's Plant Propagation, edited by Alan Toogood (DK Publishing, 1999) says to take softwood and greenwood cuttings in late spring or early summer. Kolkwitzia amabilis is known to root easily from cuttings, and the new plants should flower in three years. The cuttings should be "two internodes or about 3 inches long; avoid thick, pithy water shoots and look out for tips distorted by aphids. Root semi-ripe cuttings in a tray or directly in pots. Rooting takes 4-6 weeks."

Season All Season
Date 2010-07-14
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Keywords: Hoya bella, Potted plants, Tropical plants, House plants

PAL Question:

My Hoya bella was recently moved outside. It flowered nicely, but now the leaves are a light yellow/green and the soil surface in the pot is covered with moss. What is wrong and what can I do?

View Answer:

Here is some information I found in the book, Subtropical plants: a practical gardening guide (by Jacqueline Sparrow and Gil Hanly, 2002, p. 107), quoted below:

Hoyas do very well in pots. They need bright light, but not sun...Hoyas strike fairly easily from cuttings, taken at the warmest time of the year.

About the yellowing of the leaves...I am pretty confident that this is due to the plant getting too much water (rain, whatever source, while it was outdoors) and the soil not drying out, which also explains what happened to the top of the soil--the moss or algae growth there. I would just gently scrape off the soil surface and put a thin layer of potting soil over it. If the plant starts getting what it needs again (as it did before it was put outdoors), it will hopefully return to its former healthy self.

During its growing season, Hoya bella prefers temps between 64 and 68 degrees; during its rest season, 59 degrees is the recommended minimum temperature (so here in Seattle, right next to a window may be too cold).

University of Florida provides additional information about Hoya bella.

Season All Season
Date 2008-01-10
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June 24 2013 12:55:25