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Elisabeth C. Miller Library

Archives: Plant Answer Line Q & A

Plant Answer Line questions and answers.

Growing wasabi in the Northwest

I would like information about growing wasabi in the Northwest, such as how to propagate it, and ideal growing conditions.

We don’t have any books in the Miller Library on wasabi propagation, and most general propagation books do not include wasabi (the plant’s botanical name is Eutrema, though there is some taxonomic disagreement over the species name, and the genus is sometimes listed as Wasabia). Cultivation of wasabi in this country is a relatively new endeavor, so the more current the source, the better. I did a journal search in Web of Science, and could not find anything on wasabi propagation or cultivation. There may simply be little information out there.

A colleague here in the Miller Library says that wasabi is a notoriously difficult-to-grow plant, and the fact that it requires cold running water throughout the year seems to preclude growing it in a climate which has freezing conditions in winter, unless you are able to protect the plants from frost damage.

Washington State University’s publication, “Growing Wasabi in the Pacific Northwest,” by Carol Miles and Catherine Chadwick, may be especially helpful to you. There is an earlier article by Miles from WSU’s Vegetable Research facility. It was published in PNW Sustainable Agriculture Newsletter in October of 1996.

Purdue University’s New Crops site offers the following information on wasabi cultivation. It contains a link to an article on growing wasabi in New Zealand, which has some climate similarities to our region.

An article on wasabi by John A. Ball includes a list of growers. You will notice that several are in the Pacific Northwest.

Although it is not specific to the Pacific Northwest, Utah State University has a concise guide to growing wasabi in the garden.

Mother Earth News also published an article on wasabi cultivation in October/November 2004.

Laurel leaves yellowing and dropping

I am losing leaves on my improved English laurel. They turn bright yellow and fall off. I have heard that some loss is normal, but I have one bush losing at least 15 leaves. They have been in the ground now for 4 weeks.

Second question if I could? When a plant turns yellow from the bottom but the top looks normal and wants to bloom what is the problem. Too much water, etc. It just a small flowering plant and the bottom is getting yellow like it is not happy but the top wants to grow fine.

I will take your second question first: When the oldest leaves turn yellow, but the top of the plant still looks fine, that is usually a symptom of nitrogen deficiency. When nitrogen is deficient in the soil, plants will move nitrogen from the oldest leaves to new leaves, resulting in yellowing, or chlorosis, of the oldest leaves. The Sunset Western Garden Problem Solver recommends using a fertilizer containing nitrogen according to directions on the label for the kind of plant you have. You did not mention what kind of plant it is. The fertilizer will give the plant a quick boost. For longer term health, blood meal or fish meal scratched lightly into soil surface around the plant (follow package directions for amount), topped with a one-inch layer of compost will improve the nitrogen content and overall quality of the soil.

(Adding an inch of compost to planting beds in early spring is a good annual practice for replenishing soil nutrients and keeping plants happy.)

You wondered if too much water could be the problem. Overwatering can produce nitrogen deficiencies in the soil by leaching nitrogen down through the soil and away from plant roots. Different plants have different water requirements. Do you know what kind of plant it is? Without knowing what kind of plant it is, and without seeing it, we can only give possible explanations.

Now back to your first question. There are lots of different patterns of yellowing of leaves and each has a different cause. Is it just the bottom, oldest leaves, or newest leaves, or all leaves, or just the edges of leaves, or just between the veins. I would need to know more before even hazarding a guess. But to get an accurate diagnosis for the problems both of your plants are suffering, we recommend you take samples of each, of good leaves and bad and a little bit of soil from around the root zone of each plant to your local Master Gardener Clinic.

You can find a Master Gardener Clinic on the King County Master Gardener website.

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Controlling Himalayan blackberry

I live next to a Washington Department of Transportation I-5 easement land where the department has let blackberries run rampant. As a result, I have thousands of blackberry seedlings in two areas of my property at this time of year. Is there any effective way to kill them at this stage?

In King County, Himalayan blackberry is a Class C noxious weed, meaning that control is not required by law, but is recommended in natural areas and restoration sites.

University of California, Davis Integrated Pest Management describes various methods of controlling blackberry.

In Ann Lovejoy’s Seattle P-I article dated, Thursday, June 7, 2001, she describes vinegar-based herbicide as a means of controlling weedy blackberries and horsetail.

You may also want to contact WSDOT’s roadside vegetation maintenance department to report the problem with unwanted blackberries migrating onto your property.

Another option, increasingly being used for large areas with invasive weeds, is to rent goats, who will eat the weeds down to the ground. The Seattle Post-Intelligencer published an article on this subject in 2007. “Rent-a-Ruminant” on Vashon Island is one example of a goat rental service.

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Native groundcovers

I am looking for a native groundcover to grow as a walkway along side my house. It is a shady spot and it would need to be a hardy plant that could be walked on.

Regrettably, there are not any native, shade-loving, walkable ground covers available unless you are interested in mosses. If that is appealing, you can check in the book Plants of the Pacific Northwest Coast by J. Pojar. The following websites may help you find native plants:
King Conservation District

King County Native Plant Guide

Washington Native Plant Society

For information on growing mosses, see the now archived page of “Encouraging Mosses” from Oregon State University, based on the writing of George Schenk.

If your heart isn’t definitely set on natives, there are some good alternatives:

  1. In her book Big Ideas for Northwest Small Gardens, Marty Wingate recommends Mazus reptans. It is semi-evergreen to evergreen with tiny blue flowers from late spring through summer. It takes full sun to part shade and is delicate looking, but takes foot traffic. It requires some fertilizer to stay perky. (Note: I use it in my garden–it is versatile and pretty)
  2. Another source of ideas is the website http://stepables.com/
    Click on plant info, then plant search.
  3. A ground cover that I have found useful (it can take car traffic a couple times a day) is Leptinella gruveri ‘Miniature.’ You’re almost certain to find it at the website above.
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Controlling lace bugs

I think my Rhododendron is infested with lace bugs. What do you recommend?

According to The Organic
Gardener’s Handbook of Natural Insect and Disease Control edited by
Barbara Ellis (Rodale Press, 1996), this problem occurs more often with
plants in full sun. The book recommends using insecticidal soap at the
first sign of damage. Spray the undersides of the leaves in particular
(and always test the spray on a small area first). Repeat the spraying in
mid- to late-summer if the lace bugs reappear. If the problem is severe,
use superior oil or pyrethrin as a last resort. There is a recipe for
homemade soap spray in the book: 1 teaspoon up to several tablespoons of
liquid soap (use unscented, nonchemical soap) per gallon of water. Start
with a lower concentration and adjust as needed. You can also add
insecticides such as horticultural oil, pyrethrins and BTK to increase
the spray’s toxicity to pests. Mix 1 tablespoon liquid dish soap and 1
cup of oil (peanut, safflower, corn, soybean, or sunflower), When you are
ready to apply the spray, mix 1 to 2 1/2 teaspoons of this soap/oil blend
with 1 cup of water. (These are just guidelines for proportions.) You can
also use commercial products, examples of which are here:
Safer Insecticidal Soap and Stoller Natur’L Oil.

University of California, Davis’s Integrated Pest Management website has
a page about lace bugs. Below is an excerpt:

MANAGEMENT

Tolerate lace bug damage where possible; in most cases, it does not
seriously harm plants. Provide proper cultural care so plants are
vigorous. No treatment will restore stippled foliage, which remains until
pruned off or replaced by new growth. If damage has previously been
intolerable, monitor plants early during subsequent seasons. Take action
when populations begin to increase and before damage becomes extensive.

Biological Control

Natural enemies of lace bugs include assassin bugs, lacewing larvae, lady
beetles, jumping spiders, pirate bugs, and predaceous mites. These
predators may not appear in sufficient numbers until after lace bugs
become abundant; their preservation, however, is an essential part of a
long-term integrated pest management program. Growing a variety of
species, mulching soil with organic material, and shading plants from
afternoon sun can reduce lace bug damage to shrubs and increase natural
enemy abundance. If applying pesticides, using only short-persistence
materials such as oils and insecticidal soaps will minimize the number of
beneficial predators and parasites that are killed.

Cultural Control

Grow plants well adapted to conditions at that site. Plants in hot, sunny
locations are more likely to be damaged by lace bugs. For example,
azaleas grown under partial shade experience less damage by the azalea
lace bug in comparison to azaleas that are drought stressed and exposed
to bright sun. Provide adequate irrigation and other care to improve
plant vigor. Prune out damaged foliage if the discoloring is intolerable
and relatively localized. Do not remove more than a small percent of a
plant’s branches during one season and use good techniques so that
pruning does not injure plants, such as by exposing inner branches to
sunburn.

Chemical Control

Contact Insecticides. Insecticides will not restore an undamaged
appearance, but can reduce or prevent further damage. Almost any
insecticide will control lace bugs if it is sprayed directly onto the
insects. Azadirachtin (Safer BioNeem), insecticidal soap (Safer),
narrow-range oil (Green Light, Volck), neem oil (Green Light Garden
Safe), or spinosad (Conserve, Monterey Garden Insect Spray, Spinosad Home
and Garden) sprays temporarily control lace bugs if insecticide
thoroughly covers the underside of leaves where adults and nymphs occur.
These IPM-compatible insecticides have very low toxicity to humans and a
less adverse impact on natural enemies than more persistent,
broad-spectrum insecticides.

Cover crops for the Pacific Northwest

I have two raised garden beds (8 x 12 feet) in my back yard. Recently I read somewhere that having a cover crop during our wet winter months would help decrease the leaching of nutrients and would also help bind nitrogen in the soil.

Three suggested cover crops were crimson clover, Australian field peas (did they mean Austrian winter peas?), and vetch.

What would you suggest? Are these good recommendations? Which
might be the best?

Sustainable Horticulture: Today and Tomorrow (R. Poincelot, 2004, p.
372-377), says,

“Cover crops, when managed as green manures, can supply considerable nitrogen
for [vegetable] crops.”

Legumes, like the pea and vetch you mentioned are
good choices for increasing the nitrogen level in soils. (Hairy vetch, Vicia
villosa, and Austrian winter pea, Pisum arvense). Crimson clover (Trifolium
incarnatum) is almost as efficient at supplying nitrogen to the soil.

Hairy Vetch supplies 33-145 lb of nitrogen per acre/year to soil, Austrian
winter pea supplies 53-100 lb/acre/year, and Crimson clover supplies 19-114
lb/acre/year.

Another species you might consider as a cover crop is Fava bean (Vicia
faba), which supplies 25-105 lb/acre/year.

Additional information about growing cover crops in the Pacific Northwest
can be found on this information sheet from the Washington State University extension.

Territorial Seed Company, in Oregon, sells small quantities of cover
crop seed by mail order, including Hairy vetch, Crimson Clover, and Fava
Bean.

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Courses on landscape design criticism

Do you know of any correspondence courses concerning landscape design criticism and critique?

There is a book called North American Horticulture–A Reference Guide, compiled by the American Horticultural Society (second edition, 1992, edited by Thomas M. Barrett). The book includes a chapter on education, including correspondence courses.

Three community colleges in the Puget Sound area offer horticulture degrees, and they might know something about correspondence programs. They are Edmonds Community College Horticulture and South Seattle College Horticulture, and Lake Washington Institute of Technology.

More colleges and universities are offering online courses now. Here are two examples :

Locating eyes on dahlia tubers

I need to find a photo of the eyes on a dahlia tuber.

There is good information on growing dahlias, including an image of the location of the eye on a tuber, at the website of the American Dahlia Society. To find the eye, locate the point on the shoulder, or crown, of the tuber from which the plant grows. The blog of Lynch Creek Dahlias (now archived) has good description and illustrations:
“Keep in mind that every dahlia tuber, to be viable, must have at least one eye, which you’ll see as tiny pointed protrusions on or near the neck of the tuber (the neck is the tuber’s connection to the central part of the root mass).”

The Dahlia Barn website also has images and instructions, as does the Summer Dreams Farm website.

Daphne odora care

I have a Daphne odora which had aphids on it early
this spring and I kept hosing it with water and got rid of the aphids
(didn’t spray with any chemicals). Lost a lot of leaves but now has new
growth. Problem now is all the leaves look wilted like it lacks water and
doesn’t seem to be growing. I have watered it real good during the hot weather
but it doesn’t seem to be working. The plant is about 7-8 years old and
has done well until this year. It gets morning sun and afternoon shade.
Am I watering too much or is it because of the heat?

Daphnes can be a bit fussy, and as this article
by Sarah Raven on Daphnes from the British paper the Telegraph mentions:

“Daphnes like life pretty constant, not too wet and not too dry, so, particularly when they’re settling in, give them a little regular watering if the rain doesn’t do it for you. They need and like good drainage, so always add plenty of organic matter (and some grit if you garden on clay). And don’t despair if your plants don’t go on forever. Daphnes rarely last more than 15 years and you’ll almost never see a shrub older than 20. Plan on taking cuttings after flowering every five years or so to make sure you always have a daphne or two in your garden.”

Signs of winter damage are similar to signs of drought problems, so it
can be confusing. The foliage can be scorched if the plant receives hot afternoon sun, but your plant is in
afternoon shade. To add to the confusion, yellowed leaves which drop can
be symptomatic of excess water AND excess drought, as well as a delayed
reaction to a cold winter. My own Daphne odora has this same problem, and
always loses some of its leaves, develops new growth, but grows slowly.
This plant requires good drainage, so that is another consideration.

Here is local gardener Ed Hume on Daphne odora:

“It is important to note that this type of Daphne needs to planted in a
spot where it gets protection from the hot mid-day sun. An eastern
location or similar spot is ideal. In addition, this one is not quite as
hardy as the others, and may need to be given some cover protection,
should temperatures dip below 25 degrees. Frost or sun burn, will show-up
in a blackening of the tips of the leaves and in severe cases the leaves
are apt to drop from the plant. The dark green evergreen leaves often
have a cream-colored margin along the outside edge.”

Another local gardening expert, Ciscoe Morris, says the following:
“These plants will thrive in the right conditions, but you will be
disappointed if you plant it in the wrong spot.Growing Conditions: Morning sun; organic, well-draining soil. Do not over-water in summer, especially in clay soil. Daphne odoras do best in morning sun and afternoon shade. Give it
well-draining soil (amend with compost). During summer, water only as
often as needed to keep it alive.”

Based on all the variables, I suggest you water it less often, and check
to make sure it has adequate drainage. This can be a challenging plant,
so be patient and hope for the best.

Safety of ceramic pots for edible gardening

My question is about the ceramic pots that you see in nurseries and
places in the area. The pots are glazed on the outside, and unglazed on
the inside, and they are made in China and Vietnam. Are these pots safe for planting vegetables and herbs? Or, are there materials in the interiors of the pots that could leach into the soil and make the vegetables and herbs unsafe to eat?

Some ceramic glazes do contain toxic materials, such as lead and cadmium.
Washington State Department of Health has information on preventing lead poisoning, and on testing for lead.

State of Oregon’s Lead Poisoning Prevention Program includes information on sources of lead exposure, including pottery.

California Department of Health has several pages on toxins in pottery.

Excerpt:

“The U.S. Food and Drug Administration (FDA) sets standards at the
national level for the amount of lead that can pass out of, or ‘leach,’
from dishes. Tableware with lead levels greater than these standards
cannot legally be sold in the U.S. The FDA regulations cover only
tableware that is imported or that is brought into the state for sale.
The standards apply only to items that are used for foods and beverages.
They do not apply to pieces that either cannot hold liquids or are not
intended to hold liquids, such as salt shakers, cookie jars, butter
dishes, etc. See the table below for the FDA standards for lead in
ceramicware.

Decorative ceramics
The FDA has labeling rules for ornamental or decorative ceramics that are
not intended for food use. These items must either (1) be permanently
labeled with a logo or statement that they are unsuitable for food use,
or (2) be made incapable of holding liquid. If an item is clearly
intended for food use, such as a bean pot, labeling it is not sufficient,
however. It must be made unusable, for example, by having a hole drilled
through any surface that could hold liquid.”

My co-worker tells me that some retail stores are good about informing customers if pots are unsafe for food use. This
document from Clemson University Extension (although its focus is
cookware) suggests that you not use pottery which does not bear the
label, “Safe for Food Use:”

If a pot has been fired at a high temperature (something you cannot
easily ascertain by looking at it), my thought would be that there would
be less likelihood of toxic material from the glaze leaching inward, but
if the clay itself comes from a source which is full of contaminants,
there may be a risk apart from the glaze. If you are at all concerned
about using these pots for growing food, my advice would be not to do it.
There are other ways of growing food in containers, such as untreated
wood boxes or barrels. See links here for general information on growing
vegetables in containers:

Vegetable Gardening in Containers from Virginia Cooperative Extension.
Plants Grown in Containers from North Carolina State University.

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