managing aphids

I have just taken over management of the small landscaped yard for my condominium and we have two trees (weeping birches I’ve been told) in the front that appear to have been infested with aphids. The trees are about 15 feet tall and are located between the building and the sidewalk to the entrance. They have southern exposure. There’s a few evergreen bushes around the trees, no grass.

I am not familiar with aphid controls, so have done some internet research, including your very useful
site. We want to avoid using pesticides, so from what I’ve read, the best control is insecticidal soap.
Before I try to spray this on the trees I have a few questions I was hoping you could answer.

1. Can you verify that this is aphid damage?
2. It seems to me that the amount of white material on the undersides of the leaves has decreased in the last month. Given that it is getting late in the growing season, is it still worth treating the trees?
3. Does insecticidal soap seem like a good treatment in this situation, and if so do you have any application tips to make sure the undersides of the leaves are treated?
4. Do you have any recommendations for preventative actions to decrease the impact of aphids on these trees in the future?

Birches are commonly afflicted with aphids, and the aphids suck sap and secrete honeydew, which can be a nuisance, and is usually why homeowners contact us. Unfortunately, if your birches are overhanging a sidewalk, it is probably getting sticky from the honeydew. Otherwise, you could probably ignore the problem (except in the most severe infestations).

You can try spraying the aphids off the leaves with a strong jet of water. You can also encourage natural predators. Avoid over-fertilizing, or exposing the trees to lawn fertilizer, for example, as this will lead to succulent new growth which attracts aphids. Make sure the trees are not under any stress, as aphids are more likely to feed on a weakened
tree. You may be able to avoid using the insecticidal soap as a control. If you do use it, you are correct that you need to reach all leaf surfaces, which is labor-intensive. Some of these soaps can cause damage, so it is always a good idea to test any such spray on a small area before coating the whole plant. An article by Colorado State University Extension provides information on insecticidal soaps. Aphids go through many generations in a year, and their eggs can overwinter.

Toxic-Free Future (formerly known as Washington Toxics Coalition) has created a document on managing aphids in the landscape.

Here are additional links on aphid control:

Aphids from University of California at Davis

Managing Aphid Problems without Pesticides from the Northwest Coalition for Alternatives to Pesticides

tree peonies care and watering

I purchased a bare root tree peony at the NW Garden Show this year and it was doing just fine, getting to be about 1.5 feet tall until about two weeks ago and the entire plant is now drooping, the leaves quickly sagging. It is in a semi-shady spot that receives morning sun. I water all of my plants once a day unless it has been raining. I am trying to figure out if it is dying, and what I might do.

My first thought is that your tree peony is either responding to drought, or too much water. My own tree peony which is about 12 years old has always been sensitive to excessive heat and drought. It is in a partly shady location, but it has root competition from two nearby conifers. Watering less frequently but more deeply is usually a good idea. A commercial nursery site has the following information about this plant’s water needs. Excerpt:

“Watering: This is the most common misunderstanding. Tree peonies do not have watering needs like roses or other perennials. They are woody shrubs native to northern China, which receives about 30 inches of rain per
year. Once established, tree peonies are drought tolerant plants. Excess water will suffocate the roots and is the leading cause of plant failure. Do not plant near auto-sprinkler systems that keep the soils continuously moist. Do not water until soil is dry below the surface and try not to wet leaves when watering to prevent fungus. Be observant; soil can dry out on top and still be moist 6-12″ below the surface. When you feel the soil is dry below the first 4-6″ and leaves may droop slightly, water the roots deeply. Climates of hot summer temperatures with little or no rain at all will require more attention to watering then those areas that get some rainfall. Peonies in root control bags will require more watering attention than tree peonies planted in the ground. NOTE: Droopy leaves in the first warm days of spring are caused by an imbalance of the root system and leaf production. If soil has moisture, do not water. This imbalance that will self correct as the plant settles into the growing season. You know this is the cause of the limp leaves if the plant recovers in the evening or early the next morning.”

The other possibility is a fungal disease called peony wilt. Here is more information about this problem, from the Royal Horticultural Society. Excerpt:

“Tree peonies can be vulnerable to attack by peony wilt (Botrytis paeoniae), especially during wet springs. Symptoms are wilting of the flower buds, sometimes accompanied by a fluffy grey mould and, later in the season, brown blotches on the leaves. Botrytis forms sclerotia (hardened fungal bodies) in diseased tissue, which carry the fungus over the winter, so it is important to prune out and destroy infected tissues to prevent this happening. Currently no fungicides labelled for control are available.”

If you think that the problem may be wilt, and would like confirmation, you can bring samples of the leaves to a Master Gardener Clinic for diagnosis.

on controlling Japanese Anemones

Do you have any suggestions for controlling the spread of some too happy Japanese Anemones? I know they spread by underground roots but do they also spread via seeds? If I put down a barrier how deep should it go?

I have also experienced this in my garden, and it is not impossible to dig up Japanese anemones and either compost them or offer them to fellow gardeners (with a stern warning!). Anemone x hybrida spreads easily by roots but can be propagated from seed. It is most likely that the spreading of the plant in your garden is mainly rhizomatous (by roots). If you don’t want to dig up the occasional clump, you could try getting rid of the plant in areas where you do not want it, and then putting barriers such as plastic edging around the clumps you want to keep, although I think this requires at least as much labor as removing any unwanted anemones. Also, cut off spent flower stalks if you want to avoid seeds. However, the seedheads are flossy and ornamental in winter.

Here is general information on this plant, from Cornell University.

Here is information from Iowa State University Extension(now archived). This may give you some ideas on ways of containing the spread of the roots.

Cedrus deodara dripping problem

My deodar cedar drips a lot and an arborist told me the tree has ongoing pest problems. Could the tree have aphids?

There are several possible causes for the dripping of your Cedrus deodara. It might be honeydew (from an insect infestation). There is a type of aphid, Cinara curvipes, the bowlegged fir aphid, which feeds on cedar bark. Large colonies of aphids can develop on the twigs or branches of host trees in the winter along the Pacific Coast, or in the spring inland. Vast amounts of honeydew can rain down if the infestation is heavy. If you shake an infested branch, aphids should drop from it.
(Source: Insects that Feed on Trees and Shrubs by Warren T. Johnson and Howard H. Lyon, 1994)

If, in addition to the oozing sap, the foliage is also discoloring and wilting, it could be caused by a root or crown rot.
(Source: Pests of Landscape Trees and Shrubs, 2nd edition, by Steve Dreistadt, 2004)

Since there could be many causes, it might make sense for you to bring in a sample to a Master Gardener Clinic. You can locate a Master Gardener Clinic within King County on this website (Plant Clinic Schedule, or statewide here.

silkworms and mulberries

What type of mulberry do silkworms eat, and where can I find this tree (I need leaves for feeding the silkworms)?

Silkworms will eat any species of Morus, though white mulberry (Morus alba) is their preferred food source.

I understand you are looking for a tree source. I wonder if you actually plan to plant the tree, or if what you really need is access to mulberry leaves. Numerous mail order nurseries carry Morus alba, Morus alba tatarica, Morus rubra, and Morus nigra, and in fact you may find local nurseries with trees, too–it’s just that they don’t keep an online inventory because it changes too frequently. You can search Plant Information Online for mail order sources. I did a quick search on Morus alba, and found several nurseries that carry it.

If you simply want leaves, you may want to check Arthur Lee Jacobson’s book, Trees of Seattle, which lists locations of trees in both private and public gardens. You would, of course, need to obtain permission to harvest any leaves.

This website offers information on real and artificial food sources for silkworms.

crocus and daffodils failure to flower

Many of my crocus and daffodils (especially crocus) didn’t flower this year. They don’t seem to be in need of separating – none of them have been in the ground for over 3 years and I don’t think I overfertilized. Otherwise they seem quite healthy. What might be the problem?

The most common reasons that hardy bulbs like crocus and daffodils fail to flower are these:

1. Planting location: they need to be planted in full sun.
Bulbs; a complete handbook of bulbs, corms, and tubers (by R. Genders, 1973)

2. Drainage or heat: spring flowering bulbs planted in poorly drained soil or too near a heated basement (where heat from the structure warms the soil and interferes with the bulbs’ necessary cold treatment) will rot or simply fail to flower.
Daffodils for Home, Garden and Show (by D. Barnes, 1987)

3. Fertilization: high nitrogen fertilizers encourage lush green growth and discourage flowering.
Daffodils for American Gardens (by B. Heath, 1995)

on propagating Clerodendrum trichotomum

When and how can I propagate a glorybower? There are suckers coming up at the base of the plant.

Regarding propagating Clerodendrum trichotomum (harlequin glorybower), the book Trees and Shrubs Hardy in the British Isles Vol. I (by W. J. Bean, 1981, p. 667) says that shrubs can be propagated by root-cuttings, or by the young suckers which frequently spring from the roots.

Since you mentioned that there were suckers (gardening term) coming up around the plant, it is most likely the species is C. trichotomum and not C. bungei (one of the others commonly grown in our climate). C. bungei, according to the same source, should be divided in the spring.

Another source, Flora, Vol. 1, (chief consultant, Sean Hogan, 2003, p. 393) says regarding Clerodendrum (genus-level information) that propagation is done by sowing seed in spring or by taking cuttings of half-hardened wood during winter or summer.

on transplanting rhododendrons

Some friends of mine just bought an old house with a huge rhododendron up against the house. It is at least 8 feet high and probably 10 feet wide. I did not dig around and there may be multiple shrubs growing next to each other. What are the chances of moving the rhody successfully? Should it be cut way back before hand? Any particular time of year for moving it?

Fortunately, rhododendrons are very likely to succeed in being transplanted. Most experts recommend fall as the best time to transplant. Spring or late winter is second best.

The real challenge is getting a large enough rootball. A five-to-six foot plant requires a rootball of about 3 feet in diameter.

Step 1- dig a 12-18 inches deep trench around the rootball.
Step 2 – under cut the rootball to sever the roots from the underlying soil. The most important roots are the small feeder roots, not the big old ones. You can use a steel cable with a tractor or you can use a shovel and digging iron and a lot of hard work. The rootball will probably be about 8 – 12 inches deep and 3 feet in diameter.
Step 3 – tilt it on its side and slide a piece of 1/2-inch plywood under the rootball and set the plant upright. Use the plywood to move the plant to its new location. (A tarp works, too, if you can get it underneath the rootball.)
Step 4 – dig a new hole 4 feet in diameter and deep enough so that the rootball is 1 inch higher than the depth of the hole. (Slightly above grade)
Step 5 – water well and mulch around the perimeter of the plant BUT keep the mulch at least 2 inch away from the trunk of the plant.

Newly transplanted plants need some tender care and especially need to be watered regularly, but not over watered.

There were no recommendations to cut the foliage back. But it is always ok to prune out dead, dying, diseased or deranged stems. This also means you can prune out twiggy growth.

This information comes from Success with Rhododendrons and Azaleas by H. Edward Reiley (1992).

shade tolerant and low maintenance groundcovers

What is a good way to deal with a gravelly area with a lot of shade? Are there good groundcovers that would be low maintenance? Can the plants grow right in the gravel, or do I need to do something to the soil?

If it’s pure gravel, you can just make a border (with rocks and/or wood, preferably non-treated) and fill it with 9-12″ of soil. (No need to remove the gravel.) You buy soil by the cubic yard, so to figure out how much, multiply the length (feet) x width (feet) x depth (.75 or 1), then divide by 27 to get the number of yards. One yard of soil is 3′ x 3′ x 3′, or 27 cubic feet. My guess is that you need less than a yard, but it settles.

You can save money by buying the soil in bulk. Otherwise, you have to buy it by the bag, and they might come in cubic feet. If there is only some gravel, you may be able to get by with the soil/gravel mix that you have. See how much hardpan there is by digging around a little.

If you have lots of weeds in the gravelly area, try mulching the whole area with a thick layer of wood chips (freely available from arborists) Smothering weeds depends upon complete darkness more than anything.

Once you’ve done that, you can plant right away. Here are some plant suggestions. I’ve
included links to pictures, but you can always find more on Google images or
the Missouri Botanical Garden’s PlantFinder.

Lobularia maritima, known as sweet alyssum: You can plant seeds of this and it will come up this year. It’s best to mix it with something else, since it dies down in winter (but self-seeds vigorously and will return). The white seeds the fastest (year to year), but it’s nice to mix with purple. Both varieties smell good and attract
beneficial insects.
Fragaria x ananassa ‘Pink Panda’: A strawberry-potentilla hybrid that grows fast and spreads easily, is good weed suppresser, and blooms twice a year with pink flowers. This is an excellent groundcover, will probably be evergreen.
Pachysandra: This plant is evergreen, and though it is not as fast growing as some groundcovers, it does spread.
Hardy Geranium spp.: Geranium x oxonianum ‘Claridge Druce’ is a variety that spreads well. Another good variety is Geranium endressii ‘Wargrave’s Pink’; in particular, it seeds itself well. Geranium macrorrhizum has many cultivars, a pleasant scent, and self-seeds readily.
Galium odoratum: Also called sweet woodruff, this plant is prettily scented, probably evergreen here, and spreads fairly rapidly. It produces white flowers in early spring, and it would be particularly good to mix with something taller, like Geranium species.
Oxalis oregana: This native plant looks like a shamrock, and though it is slow to establish, once it has it’s very
tough and spreads. If you don’t get the native Oxalis oregana be careful, as the other species are very aggressive.
Euonymus spp.: These woody groundcover plants are evergreen, and come in lots of varieties like
E. fortunei ‘Emerald ‘n’Gold’ and ‘Emerald Gaiety’. Do be sure to get a groundcover and not a shrub version of the plant. ‘Emerald and Gold’ is the most robust choice.
Convallaria majalis: Also known as lily of the valley, this is a vigorous (aggressive!) groundcover.
Maianthemum dilatatum: Called false lily of the valley, this native plant is a good choice for shade groundcover.
Polystichum munitum: The native swordfern (or another fern species) might work. P. munitum is basically evergreen, though you might need to cut out some dead fronds in late winter, and makes a good mix with something else. Other deciduous ferns are higher maintenance.

There are also a couple of plants to avoid!

DON’T plant Aegopodium podagraria ‘Variegatum’: Commonly called bishop’s weed, and frequently used as a groundcover, this plant is very invasive.
DON’T plant Lamium galeobdolon (formerly known as Lamiastrum), either: Yellow archangel is very invasive in Pacific Northwest forests.

on eradicating comfrey roots

Comfrey root has taken over my acreage at my home. I want to know how it spreads, how to kill it, naturally and chemically, by the root. I am currently using Roundup sporadically. I don’t know how it got into my yard or anything. I would like to be able to kill it off and plant nice grass there in the spring.

Comfrey (Symphytum officinale) has a fibrous root system which is very deep and difficult to eradicate. Any bits of root left in the soil can produce new plants. While it may be tempting to take the quick path and use RoundUp to get rid of your comfrey, you may want to consider the health and environmental consequences of this product, whose active ingredient is glyphosate. Northwest Coalition for Alternatives to Pesticides has information about this chemical.

If you avoid using herbicide, you may find additional uses in the garden for the comfrey you remove by hand. Do not rototill this plant, and always wear gloves when handling it. Dig carefully and remove as much as you can of the roots, and then dispose of them. Pacific Northwest gardener and author Mary Preus writes about comfrey in The Northwest Herb Lover’s Handbook (Sasquatch Books, 2000):

Comfrey can play an important role in compost making, The considerable leaf mass of a mature comfrey plant, cut several times in a season, can add plenty of high-nitrogen green material to the pile. In addition, the leaves contain calcium, phosphorus, potassium, and trace minerals drawn deep from the subsoil. Just be sure there are no ripe seeds, and that no pieces of root are attached to the base of the leaves that go into the compost pile.

The leaves can also be added to potato crops as a fertilizer. After allowing them to wilt, you can use the leaves by chopping them up and placing them in a trench with main crop potatoes. As the leaves are high in potassium, they make an excellent fertilizer. Layer to a depth of 1 to 2 inches. Comfrey can also be used on other plants that benefit from high doses of potassium, like tomatoes and runner beans. It has also been used to as a top dressing around soft fruit bushes. As the leaves break down, gently cultivate them into the planting area. There is an article from the Permaculture Research Institute about the uses of comfrey, The Wonderful Multi-purpose Comfrey Plant, by Melissa Miles (October 1, 2010).

If you have large swathes of your garden which are weedy, you can also try mulching with a thick layer of arborist wood chips (free from arborists and websites like Chip Drop) as a solution. This is now considered preferable to sheet mulching with layers of cardboard and newspaper, which do not do a good job of suppressing aggressive weeds, and can also harbor pests. When you are ready to plant again, you will need to rake away wood chips in the spots where you are placing your plants.