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Elisabeth C. Miller Library

Archives: Plant Answer Line Q & A

Plant Answer Line questions and answers.

on the Mucuna species

I saw an interesting flowering vine growing in Japan, and I am wondering what it is and if I can grow it here in Seattle. It has very dark purple (almost black) claw-like flowers and fuzzy stems. Is it purely ornamental, or does it have other uses?

 

The plant you saw is a species of Mucuna, probably Mucuna pruriens or Mucuna nigricans. M. pruriens has various common names: velvet bean, and cowhage or cowitch (from the Hindi name, kiwach, which means “bad rubbing,” and refers to the extreme itching—pruritus–that contact with the stinging hairs on the pods causes). You might be able to obtain seeds and grow it here as an annual, but it prefers tropical regions and is native to southern China and eastern India.

The plant has uses in Ayurvedic medicine and is also considered an analog of the hallucinogenic ayahuasca. According to the scientific article “The Magic Velvet Bean of Mucuna pruriens“ (Lampariello et al. Journal of Traditional Complementary Medicine, 2012 Oct-Dec), the pods are used as a vegetable for human consumption, and its young leaves are used as animal fodder in parts of Asia, Africa, the Pacific Islands, and America.

Strangely, the beans are sometimes used with malice, to cause discomfort, as this information from the Centers for Disease Control explains:
“On October 6, 1985, a Paterson, New Jersey, Fire Department ambulance responded to a call reporting two people with severe pruritus. On arrival, the two emergency medical technicians (EMTs) found a Spanish-speaking couple living above a beauty salon who described severe itching, which they attributed to ‘voodoo beans’ found in their beds. They displayed several fuzzy bean pods. Soon after their arrival, the EMTs developed pruritus. All four individuals went to an emergency room complaining of itching and skin discomfort. On examination, both members of the couple had erythematous macular rashes on their extremities and bodies; the EMTs had rashes on their arms. There were no respiratory problems. Because of the unknown etiology of the symptoms, two were given epinephrine injections; the others received antihistamines and topical steroid cream. Symptoms resolved within 1-2 hours of treatment. The admitting nurse, who put an arm around one patient, developed a pruritic erythematous area on her inner forearm approximately 20 minutes later. This resolved an hour after washing her skin with soap and water. A policeman who went to the apartment and a worker who collected trash outside the following day also developed itching and received similar emergency-room treatment. Patrons and employees of the shop below and neighbors of the couple had no similar symptoms over the 2-day period.”

If you do decide to grow this interesting plant, only handle it while wearing substantial gloves.

The seeds of some species of Mucuna (those called “sea beans”) are used in making jewelry. Here is an excerpt from Wayne’s Word (a natural history website):
“[the flowers] are pollinated by night-flying bats that sip the sweet nectar and transfer pollen from one plant to another. After pollination, the ovary of each flower develops into a legume pod containing several large seeds resembling miniature hamburgers. They have a hard, thick, woody seed coat which makes them impervious to water. Internal air cavities also make them buoyant in water. The conspicuous, dark, central attachment scar (hilum) produces the layered appearance, and their superficial resemblance to a miniature hamburger. Sea beans are washed down gullies and creeks where they are carried into rivers that eventually flow into the Atlantic or Pacific oceans. The buoyant seeds drift for months (or years) at sea, eventually washing ashore on the sandy beaches of a distant continent or tropical island. They are often collected and polished by natives and made into lovely necklaces and bracelets.”

Ladybugs: benefits and drawbacks

Ladybugs: are they beneficial? Invasive? I know that nurseries sell them for release into the garden. Is that a good idea?

 

The type of ladybug most often for sale is an introduced species. This factsheet from Linda Chalker-Scott of Washington State University provides a thorough explanation of why it is problematic.

Multicolored Asian lady beetles are generalist predators and they can be beneficial in the garden, but they also displace the North American native species of lady beetle. Purchasing them is not recommended and is probably a waste of money because, well, they have wings, and they will fly away. Former University of Washington Botanic Gardens director Sarah Reichard’s book, The Conscientious Gardener, advises that you instead avoid using insecticides so that your landscape will naturally attract beneficial insects, particularly native ones.

Another drawback of releasing ladybug larvae in your garden is that they sometimes find their way indoors, where you don’t want them to be. The multicolored Asian lady beetles (Harmonia axyridis) look for crevices to spend the winter hibernating and they seem particularly fond of light colored south walls. If you don’t want to find thousands of these beneficial insects flying around your house on the first sunny day in spring, fill the cracks in your house siding with caulk. For a description, management ideas, and detailed vacuum cleaner bagging instructions, Ohio State University Extension has a fact sheet on these insects. Inside a home, the insect droppings are a human health hazard, and can trigger asthma and other allergic reactions.

on bitter cucumbers

Some of the cucumbers I am growing and harvesting taste just fine, but some are really bitter—I wonder if I should even be eating them. What causes this, and are they safe to eat (not that I want to)?

 

What you are describing actually has a name, toxic squash syndrome. It can affect plants in the Cucurbit family (so not only cucumbers but also zucchini, winter squash, and even melons). Here is a Master Gardener article from the Sequim Gazette about cucurbitacin poisoning. A 2012 factsheet (no longer online) from Oregon Health & Science University about this problem says that the cucurbitacins produced by plants in this family may have benefits for the plants themselves, warding off insects. But in humans, excessive cucurbitacin can cause digestive distress. Wild plants tend to have higher levels of this naturally occurring substance than varieties bred for human consumption. Still, environmental factors (such as uneven watering or fluctuations of heat and cold) can cause normally tasty cucurbits to turn bitter.

A 2007 article from North Carolina Cooperative Extension, “What Makes My Cucumbers Taste Bitter,” says that cucurbitacin is mostly found in the leaves, stems, and roots of the plants but it can spread to the fruit as well. In your cucumbers, the highest concentration is likely to be in the skin and just below the surface of the skin. “Misshapen fruits are more likely to be bitter than well-shaped fruits. Some scientists even think that varying levels of fertilizers, plant spacing and irrigation frequency may also affect cucurbitacin levels. Bitterness seems to vary with the type of cucumber grown.”

Because of the potential for unpleasant side effects, I suggest not eating the rest of a cucumber (or any other member of the Cucurbit family) if the taste is bitter.

vermicomposting best practices

I have read about the problem with earthworms invading forests and overeating the duff, forest floor, disturbing the local biosystem, etc.

What about in our Puget Sound area? Is this a threat, and should we be concerned about worms escaping from worm bins and vermicomposting projects?

 

If you have a worm bin, be sure that the worms inhabiting it are red wiggler worms, Eisenia fetida (the kind which are ideal for vermicomposting), and never dispose of the contents of a worm bin in a wooded area.

According to former UW Botanic Gardens director Sarah Reichard’s book, The Conscientious Gardener (University of California Press, 2011), “where native worms already exist, new introductions […] may overconsume local food sources. But perhaps the most serious problems occur where there are no native worms, such as the northern temperate forests of North America […]. There, the worms modify the soil structure, affecting the flora and fauna.” Reichard recommends that gardeners not use soil with worms in it as fill dirt, and not dispose of nursery material with worms in it, especially in a wooded area. To be cautious, you can freeze your worm bin compost for one to four weeks to kill the worms. Be sure the supplier of your composting worms is knowledgeable about the species of worm they are selling. Reichard says: “…better yet, do not use worms at all: let naturally occurring organisms break down the waste.”

The invasive worm problem is a major issue in places like Minnesota. Here is information about that state’s attempt to prevent earthworm invasions of forest land. Note that they say Eisenia fetida (red wiggler) is safe because it will not survive winter temperatures. Our winters are not as cold, but I did not find any documentation to suggest that red wiggler worms are a problem in the Pacific Northwest.

Lady Bird Wildflower Center (in Texas) replied to a question similar to yours:

Excerpts:
“The bottom line is that in the far northern deciduous forests there is great concern over the presence of exotic species of earthworms because of their effect on the soils; while in the unglaciated southern regions, although there is some concern, the impact of the exotic species on soil processes is of minimal concern.
“The habitat and available food will define where exotic species can live. Eisenia fetida lives in surface soil and its food is leaf litter, microbes, and soil with high organic content. Hendrix and Bohlen (Hendrix, P. F. and P. J. Bohlen. 2002. Exotic Earthworm Invasions in North America: Ecological and Policy Implications. BioScience V. 52, no. 9, pp. 801-811) say: ‘Earthworms species from northern latitudes (e.g., European lumbricids and some Asian megascolecids) are poor colonizers in tropical or subtropical climates (except in localized temperate situations), and vice versa. For example, despite continued and widespread introduction throughout the United States, Eisenia fetida, the lumbricid “manure worm” commonly used in vermicomposting, is not often found in natural habitats in the southern United States.”

As far as I know, the only endangered native earthworm species in our state is the Giant Palouse Earthworm. Nevertheless, it’s prudent not to release your vermicomposting worms into the wild anywhere.

controlling woolly aphids on apple trees

Is there something I can do to prevent my apple trees from getting woolly aphids? I’d rather not have to spray anything.

 

Encouraging beneficial insects is one step you can take. A 2013 study at Washington State University found that planting Alyssum flowers attracted syrphids which did a good job of reducing woolly aphid populations. Here are highlights of the paper that was published based on the study’s findings:

  • Sweet alyssum flowers had the highest attractiveness to syrphids.
  • Faster suppression of woolly apple aphid occurred on trees closer to alyssum flowers.
  • Higher densities of natural enemies were observed near sweet alyssum plantings.
  • Natural enemies were found to move between sweet alyssum and adjacent apple trees.

As Washington State University’s HortSense website (search under “tree fruit,” “apple,” then “aphids”) indicates, encouraging beneficial insects is a good practice for the control of all 3 main types of aphids affecting apples, be they woolly, rosy, or green:

  • Control honeydew-feeding ants, which may protect aphid colonies from predators.
  • Encourage natural predators including ladybird beetles, lacewings, syrphid (hover) fly larvae, and parasitic wasps. Avoid use of broad-spectrum insecticides which kill these beneficial insects.
  • Hand-wipe or prune to control small, localized infestations (when practical).
  • Provide proper nutrition. High levels of nitrogen encourage aphid reproduction. Switch to a slow-release or low-nitrogen fertilizer.
  • Wash aphids from tree with a strong stream of water before leaves curl.

Berberis species and their blooming time

A couple of questions: first, what’s the correct name these days, Mahonia or Berberis? Secondly, I’m trying to plant a succession of flowering Mahonia (or Berberis?) to attract hummingbirds to my Seattle garden. I have Mahonia X media ‘Charity.’ In what order do various species bloom?

 

The current accepted name for Mahonia is Berberis. I checked several local sources to compare flowering times for different species:

In approximate blooming order, here are several Berberis species:

  • Berberis x media ‘Charity’ and other cultivars (December-January)
  • Berberis repens (February-March)
  • Berberis aquifolium (as early as January but peaks March/April, into May)
  • Berberis bealei (“early spring,” according to Gossler)
  • Berberis nervosa (May)

pests affecting currant trees

We moved into a new house which has a large currant or gooseberry bush. Now that it has leafed out there are numerous caterpillars eating the leaves. I know they are not tent caterpillars, but I cannot identify them. They are whitish-green with yellow bands across the top and bottom, with many black dots or bumps. The head and first six legs are black. It would be nice to learn more about them.

 

I cannot make a conclusive pest identification remotely, but there is a possibility these caterpillars are currant sawfly, or imported currantworm. Here is some information about this pest from the Pacific Northwest Pest Management Handbooks.

If this pest is the culprit, the book, The Organic Gardener’s Handbook of Natural Insect and Disease Control edited by Barbara Ellis (Rodale Press, 1996) recommends using Pyrethrin spray, spraying into the center of the bush. Bees are severely affected by this pesticide, so follow the guidelines shown on this University of California, Davis Integrated Pest Management page. Also see this guide to reducing bee poisoning from pesticides.

For a definitive pest identification, you may want to bring a sample of the pest and its damage to a Master Gardener Clinic.
Using the following link, you can locate a Master Gardener Clinic in your part of Washington State.

Japanese Maples and Verticillium wilt

I want to test the roots of our Japanese Maple for Verticillium wilt. Are there places which could test for that?

 

There is information about Verticillium wilt and how to manage it on the Washington State University Extension’s HortSense website.

To have a sample from your Japanese maple diagnosed, you can take samples to a free Master Gardener Clinic, or you can send samples (for a fee) to
WSU Puyallup Research and Extension Center:

go to “How to Submit a Sample,” scroll down to “Plant Problem Diagnosis,” then you can download a form by clicking on “Form C1006.”

My personal experience with this disease is that the Japanese maple lived with it for quite a few years before totally succumbing, at which point we had it removed by an arborist. If you need to remove the tree, you may want to consult this list of plants that are susceptible and resistant to Verticillium.

deer-resistant plants

Do deer commonly eat Erythronium (dog-tooth lily)? I enjoy them (the plants) in a semi-protected area near the house, but would like to put them in with ferns in an area where we know deer have eaten other plants. I don’t want to spend the effort and money this fall if it is something they love.

 

There is probably no plant that deer won’t at least try once. Dog-tooth lily is not the common name I’ve heard most often for this plant; it is more commonly known as dog-tooth violet or trout lily. Unfortunately, it looks like Erythronium is considered a delicacy, according to this U.S. Forest Service page on Erythronium grandiflorum, a species called glacier lily, but the same genus as dog-tooth violet. Here is an excerpt:

IMPORTANCE TO LIVESTOCK AND WILDLIFE :
Glacier lily is an important forage for grizzly bears, which dig for the corms in spring. Ground squirrels will also feed on corms. Foliage is grazed by large ungulates such as sheep and cattle. In an Idaho study, glacier lily made up the bulk of mule deer diets during May.

PALATABILITY :
In Idaho, mule deer ate disproportionate amounts of glacier lily
compared to its availability, suggesting there was some preference for
the lily. Bears will stray from their normal course of travel along ridges to seek out glacier lily corms. Glacier lily provides fair to poor forage for cattle, sheep, and horses, and fair graze for small mammals, deer, and elk.

There are lists available of plants deer “won’t” eat (or won’t like, once having tried them). Washington Department of Fish and Wildlife’s Living with Wildlife website (based on the book of the same name by Russell Link) has additional information. If you scroll down, you will find a list of “Deer-Proof (or close to it) Plants for Washington Landscapes.”

 

on pruning combination fruit trees

I have a five-variety dwarf apple tree that is doing well, but seems to be developing a very strong central leader. (I planted it last year.) Is this going to be a problem? I seem to remember hearing that I shouldn’t let it do this, but I can’t find any information about how to prune this type of apple tree.

 

As I suspected, the answer to your pruning question was lurking in the pamphlet I received many years ago with my Raintree Nursery tree order. Here is what they say about “combo fruit trees” and their care:

“Combination fruit trees with several varieties on the same plant can be a fun way to grow lots of varieties in a limited area. They can be somewhat challenging too. Often one or more varieties (branches) will be much more vigorous than others. If this problem isn’t carefully addressed, then the tree can become more and more lopsided and the most vigorous varieties will overgrow the others and dominate the tree. Prune back the most vigorous branches upon arrival (if we haven’t already done so) to even out the branch lengths. Prune the most vigorous branches back again in the summer to maintain a balance. The most vigorous branches are the most upright. Spread the branches if they are supple enough to spread without breaking. If you keep any upright branches and they are too stiff to spread, cut them back, if possible to the lateral side branches. The combos should be grown as open center trees. On most combo trees, the varieties are named on the plastic label attached to the tree with the bottom budded variety listed first, the second from the bottom listed second and so on. Missing varieties are crossed out on the label.”

University of Minnesota Extension has information on open center pruning.

Oregon State University Extension has a good general guide by Jeff Olsen to Training and Pruning the Home Orchard.