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.

eradicating Yucca plants

Our home in Seattle came with a large number of established Yucca plants, and we would like to get rid of them. However, they are quite stubborn. We’ve tried a few things, including digging them up, but the root system seems quite deep and extensive and they always come back, and quickly! Any suggestions? I’ve thought they were non-native, but I guess they could be the sort that are found in eastern WA. Are there invasive species here in western Washington?

As you have observed, Yucca is very difficult to eradicate completely. Most of the literature on the subject suggests using herbicide, but even this may be ineffective, which makes the risk of using harmful chemicals to control the plant seem even less worthwhile. There are quite a few informal discussions on how to get rid of this plant on various online gardening forums, and one mentions local gardening expert Ciscoe Morris’s method for getting rid of unwanted Yucca:

“…he cut it back to ground level and put a couple of squares of heavy cardboard over it, piled on some compost/bark to hide the cardboard. I’m not growing yucca, but he said it really worked for killing it without
breaking your back. Leave in place for a year.”

The technique described here is called sheet mulching. This involves laying down overlapping layers of cardboard and then covering thickly with leaves, compost, and other materials. Agroforestry.net offers information on how to do this. StopWaste.org provides additional helpful information.

You may want to try a different approach, because current thinking is that sheet mulching with cardboard is not effective or a good idea. Freely available arborist wood chips make a good mulch, and if laid thickly enough over the area, they should help suppress regrowth of the Yucca.

Yucca is not (yet) considered invasive in our state. Here are links to information on locally noxious weeds.
Washington Noxious Weed Control Board.
King County’s Noxious Weed Control Program.

origins and spread of Phytophthora

Will the heavier than normal rainfall this fall and winter create an increased problem with Phytophthora this year? Is there anything we can do now or in the Spring to prevent a Phytophthora problem? Is there a chemical we should spray, and when?

We have numerous Rhododendrons, Azaleas, Heather, Camellias, etc. There are areas of our gardens where puddles have formed during, and remain for the day after, heavy rains. Some areas probably have a clay lens of soil underneath that is preventing good drainage, and others may have a mass of roots preventing the good drainage.

We’ve had Phytophthora before in two groupings of Rhododendrons (2 different varieties). We removed those plants, drenched the soil with the recommended chemical, waited a year, then replanted the same varieties as before. It seemed that things have been fine for at least the past five years, but now, seeing puddles, I’m concerned. Suggestions?

Phytophthora is a fungus which favors our cool, wet conditions and also tolerates heat and drought, so you may be correct that the heavy rainfall will intensify the problem. Here is a link to a September 2011 article from the journal Digger by Niklaus Grunwald, which discusses the origins and spread of the disease.

Here are some links to PDF documents with further information:

Oregon State University information about Phytophthora ramorum (sudden oak death) for forest managers and nursery operators

Toxic-Free Future (formerly Washington Toxics Coalition) has some information on Phytophthora root disease

You can ask when buying plants from local nurseries if their stock has any known problems with this fungus, and you can avoid purchasing affected stock, or planting especially susceptible host plants. If you have walked in an area where the disease is present, clean your shoes before walking in unaffected areas.

The Pacific Northwest Landscape Integrated Pest Management Manual published by Washington State University Extension (3rd ed., 2002) recommends the following methods of managing the root-rot (rather than leaf damage) manifestation of Phytophthora in Rhododendrons and Azaleas (your message does not indicate how your plants were affected by Phytophthora).

1. Plant resistant species and hybrids.
2. Avoid drought stress or flooding, high salinity, or poor drainage. The drainage issue sounds like one you should address in your garden.
3. Remove and destroy diseased plants.
4. Use clean water low in salts, and avoid splashing soil on plants when watering.

More information, from University of California, Davis’s Integrated Pest Management web site, indicates that the best way to prevent the disease is to provide good drainage and practice good water management. Here is more information from U.C. Davis.

public speakers on environmental issues

I am interested in finding a speaker in the Seattle area who can talk about environmental issues, such as conservation, ecology, sustainable gardening, and so on. Can you help?

You can try contacting Seattle Tilth at 206-633-0451, or email them at tilth@seattletilth.org.

Plant Amnesty may be able to help you (206-783-9813), or email them at info@plantamnesty.org.

Other resources include:

Seattle Audubon (206-523-4483)
The Nature Conservancy (Washington State) at 206-343-4344
Toxic-Free Future (formerly known as Washington Toxics Coalition)
Washington State chapter of The Sierra Club

King County (Washington) Master Gardeners maintain a speakers list. The speakers address a wide variety of gardening topics.

The Arboretum Foundation has also had a speakers list. I’m not sure whether it is maintained now, but you could ask at info@arboretumfoundation.org.

on the use of Casoron and Preen for weed control

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

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(now archived) and Extension Toxicology 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.

Toxic-Free Future (formerly known as 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.