Skip to content
Elisabeth C. Miller Library

Archives: Plant Answer Line Q & A

Plant Answer Line questions and answers.

Growing Magnolias in containers

I recently purchased a magnolia that had no tags on it. I have an extremely large pot that I would like to plant the magnolia in. My books at home lead me to believe that I should plant it in Azalea and Camellia potting mix. A local nursery has advised me that this would be fine, although another has said no. They also disagreed with my plan of putting rocks, bitumen, and old leaves in the bottom of the pot to help with drainage. They believe a quality potting mix and nothing else is the way to go. What are your suggestions?

Here is what the book, Magnolias: A Gardener’s Guide, by Jim Gardiner
(Timber Press, 2000) says about growing Magnolias in containers:

…considerable experience is needed to retain magnolias in a container
for any length of time. The roots are particularly sensitive to being hot
and dry during the summer months and frosted during the winter months…
Evergreen magnolias and clones of Magnolia grandiflora, in particular M.
grandiflora ‘Gallissonniere,’ can be grown in very large containers for
indoor use in atria.

I think if you take the matter of extreme heat and cold into
consideration, you should be able to grow your magnolia in a container. I
would be curious to know which species you have, because some get very
large, and for these a container might not be a good choice.
Magnolias prefer good, free-draining acidic soil that does not dry out,
according to Rosemary Bennett’s book, Magnolias (Firefly Books, 2002).
Since Azaleas also prefer acidic soil, the idea of using Azalea and
Camellia potting mix makes sense.

You may find the following information on growing trees in containers
helpful:

Virginia Cooperative Extension: Trees for Landscape Containers and Planters

University of Tennessee Extension: Trees to Plant in Containers or Wells

UBC Botanical Garden Forum: A discussion on requirements for magnolias in containers

UBC Botanical Garden Forum: A discussion on potting guidelines for a particular magnolia This discussion suggests that the container should be filled with soil-based compost which provides some nutrients to the plant.

As for container drainage, here is what Prof. Linda Chalker-Scott of Washington State University says. In short, she says that putting coarse material in the base of a pot for better drainage is a myth.

,

Seed libraries in Seattle

Are there any seed libraries or seed exchanges in the Seattle area?

Yes, there is the King County Seed Library which currently has several locations:
At the Northeast Seattle Tool Library 2415 NE 80th St Seattle, WA 98115
At the Phinney Neighborhood Center Tool Library 6532 Phinney Ave NE Seattle, WA 98103
Seattle Farm Co-Op 1817 S Jackson Place Seattle, WA 98144
Pickering Garden 1730 10th Avenue NW Issaquah, WA 98027
Hillman City Collaboratory 5623 Rainier Avenue S. Seattle, WA 98118

You might also look out for local celebrations of National Seed Swap Day, which happens on the last Saturday of every January.

The best-known national organization devoted to seed-saving and distribution is the Seed Savers Exchange in Decorah, Iowa. Another example is the Hudson Valley Seed Library in New York State. Both of these organizations sell heirloom and unusual seed varieties.

You might see if your local public library (the kind which lends books and other materials) is interested in following the example of Tucson, Arizona’s Pima County Public Library, which maintains a seed exchange.

Some local horticultural organizations have organized seed exchanges among their members, such as the Hardy Plant Society of Washington and the Northwest Perennial Alliance, but these are primarily seeds of ornamental plants. You can also start your own informal exchange by learning about seed-saving and passing along that knowledge (and its fruits–that is, seeds!) to your friends. The Miller Library has many excellent books on saving seeds. You can search the online catalog, using keywords such as ‘seed saving.’You can also check the calendar of plant sales and gardening events that the library maintains, as sometimes there are seed-sharing opportunities posted.

, ,

Effects of nectar-nicotine on bees

I am about to plant Nicotiana mutabilis seeds, and I wonder: if neonicotinoid insecticides are harmful to bees, is the pollen in Nicotiana also harmful? Also, is it a bad idea to plant Nicotiana near my tomatoes (could it spread tobacco mosaic virus)?

Although neonicotinoids are not currently implicated as a direct cause of Colony Collapse Disorder, the Xerces Society for Invertebrate Conservation’s “Are Neonicotinoids Killing Bees?” says that “recent research suggests that neonicotinoids may make honey bees more susceptible to parasites and pathogens, including the intestinal parasite Nosema, which has been implicated as one causative factor in CCD.” The brief summary of the full report on this issue is well worth reading.

I doubt whether the pollen or nectar of the ornamental plant Nicotiana has the same properties as a formulated systemic pesticide which contains a synthetic form of nicotine. For an example of the ingredients in a neonicotinoid pesticide, see this fact sheet for Imidacloprid from the National Pesticide Information Center. I found a scientific article (“The effects of nectar-nicotine on colony fitness of caged honeybees” by N. Singaravelan et al., in Journal of Chemical Ecology, January 2006) which says that the floral nectar of Nicotiana species and of Tilia cordata contains trace amounts of nicotine. The authors concluded that “results indicate that honeybees can cope with naturally occurring concentrations of nicotine, without notable mortality, even when consumed in large quantities for more than 3 weeks.”

As for your other question, Nicotiana does sometimes get tobacco mosaic virus, though the National Garden Bureau (in a link no longer available online) says the plant seldom has much trouble from it. Still, it is probably a good idea to keep some distance between your Nicotiana and your tomatoes (and any other solanaceous plants, like potato, eggplant, pepper) just to be on the safe side, or at least be sure to change gloves and clean tools after handling the plants. The main method of transmission of tobacco mosaic virus is “mechanical,” that is, by handling a plant with the virus and then handling plants that are susceptible to it.

, ,

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.

,

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.

, ,

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.
,

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.

, , , , ,

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 :