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Elisabeth C. Miller Library

Archives: Plant Answer Line Q & A

Plant Answer Line questions and answers.

Katsura trees’ soil needs

I have some dying Katsura trees. I created a dry stream to one side of them to redirect water (they don’t like wet roots). The owner has put 1-2 inches compost/soil down for some good nutrition and a few tree stakes into the area. There is also landscape fabric (the gray kind rain can get through) and another inch of bark to stop a horsetail problem that creeps in every year.

I am wondering if the the soil around the tree roots has become compacted by rains and is prohibiting the trees from getting oxygen through their roots. The yellow is not in leaf veins like an iron deficiency usually looks; it is almost as if the plant is getting its chlorophyll drained from inside. No bugs present to my knowledge either. I would like to know both what I might do about the soil and about the trees.

Some solutions to the problem may be to take some dead branches or stems to a Master Gardener clinic and ask them to help you identify what could be happening. You may also want to check that the compost is not closer than 4 inches from the trunk of the trees. If it is, scrape it away. For further evaluation of the soil, take a sample from around the tree and send it to a lab for analysis. Our website has a Soil Testing Information section that includes a list of labs that do soil test analysis. Check the area for drainage by digging a hole and filling it with water or let the rain do it and then see how long it takes to drain away. Perhaps you have a layer of hardpan clay underneath the trees that is blocking the drainage in winter and preventing the water from getting to the roots in summer.

A great resource on Katsura trees (Cercidiphyllum japonicum) is Dirr’s Hardy Trees and Shrubs: An Illustrated Encyclopedia by Michael A. Dirr. The author notes that the tree requires ample moisture in the early years of establishment. From the book, Trees and Shrubs for Pacific Northwest Gardens, by John A. Grant and Carol L. Grant, Katsura trees prefer deep soils and adequate summer moisture. There is a Katsura planted in the Arboretum on the edge of a pond in soil that is permanently wet and it is doing just fine.

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Hawaiian caper

While visiting the Kona side of Hawai’i, I noticed a low shrubby plant with stunning white flowers that had many long stamens. Can you tell me what its name is (both the scientific name and common name)? Is it something that could grow in a Pacific Northwest climate?

The plant in your picture is Capparis sandwichiana, or Hawaiian caper. Your description pinpoints one of the most striking features of this shrub, its numerous, showy stamens. In Hawai’i it is called maiapilo or pua pilo. According to A Tropical Garden Flora by George Staples and Derral Herbst (Bishop Museum, 2005), it prefers the hot sun and salt spray of coastal coral flats, rocky cliffs, or exposed lava flows further inland. It is used in rock gardens, and as a ground cover in seaside gardens, and on slopes and banks. The plant has traditional medicinal uses for treating skin, bone, and joint injuries. The name pua pilo, ‘stinking flower,’ is a bit of a misnomer. The flowers, which open at sunset and last only one night, are sweetly fragrant. It is the cucumber-shaped ripe fruit and the leaves (when handled) that are malodorous. It does not produce the capers that are known for their culinary uses. Those capers come from the buds of Capparis spinosa.

According to the United States Botanic Garden, Capparis sandwichiana is vulnerable in its native range (Endangered Species status) due to development of the Hawaiian coast and lowlands.

Neither species of Capparis would thrive in the Pacific Northwest. Capparis sandwichiana is suitable for Zone 11. Capparis spinosa, a Mediterranean species, is Zone 8-10, but at zone 8b, we are a marginal location for this plant. Pacific Northwesterners who yearn to make their own edible capers can try pickling Nasturtium seeds, as described in this Oregonian article (August 2, 2009, Vern Nelson). I suspect, however, that it is the flowers that captured your imagination!

Trachystemon orientalis as a ground cover plant

A mail-order nursery catalog I recently browsed is touting Trachystemon orientalis as the plant for problem areas of the garden where other plants would struggle. They say it will rapidly cover blank or weedy areas in the garden, whether they are sunny, shady, wet, or dry. What can you tell me about it? It sounds intriguing, but I’m worried it might be invasive!

Trachystemon orientalis is in the same family as borage (Boraginaceae), with similar blue flowers and rough leaves (to my eye, it’s a plant for a wild garden, with its resemblance to borage and comfrey). According to Perennials by Roger Phillips and Martyn Rix (Firefly Books, 2002), it is a native of eastern Bulgaria, northern Turkey, and the western Caucasus region. It is naturalized in parts of England. The authors say it thrives “in wet beech forest on shady river banks and on damp rocks at up to 1000 meters, flowering in March-May.” It spreads by rhizomes and is tolerant of neglect. Its preferred site is moist shade, but it adapts to a wide variety of conditions, and excels at smothering weeds. There is additional information from Missouri Botanical Garden.

You may be right to wonder when a plant seems to be just the thing for almost any spot, and when it is promoted for its ability to spread easily. Some ground cover plants hover on the brink between covering the ground you want covered, and exceeding those boundaries. Trachystemon‘s common name is Abraham-Isaac-Jacob. The origin of that name is unclear, but my interpretation is that a plant named for the patriarchs of Genesis has a connection to generational continuity, a fitting name for a plant which is skilled at self-propagation!

See garden writer Margaret Roach’s blog post entitled “A Plant I’d Order,” and notice what she says about the likely behavior of this plant in the Pacific Northwest.

Trachystemon orientalis is included in the Manual of the Alien Plants of Belgium and
is listed in the Invasive Species Compendium. You could test its behavior in your garden for a season or two, and if it shows signs of aggression, you should still be able to eradicate it. If your aim is to be cautious, you may want to avoid planting it.

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On the source of culinary cinnamon

Which plant is the source of the cinnamon that’s usually sold in the grocery store as a spice?

There is a fair bit of confusion about culinary cinnamon. According to Edible: An Illustrated Guide to the World’s Food Plants (National Geographic, 2008), the more common source of grocery store-bought cinnamon is Cinnamomum aromaticum, which is also known as cassia or Chinese cinnamon (and should not be further confused with plants in the genus Cassia!). You might also come across Indonesian cinnamon, which is Cinnamomum burmannii. ‘True’ cinnamon which you might find in a specialty store is Cinnamomum verum (formerly known as Cinnamomum zeylanicum), a species which is native to Sri Lanka and India. It is usually somewhat lighter in color, with a more subtle flavor. To compare and contrast these three different species, see the U.S. Department of Agriculture’s taxonomy pages for Cinnamomum verum, Cinnamomum aromaticum, and Cinnamomum burmannii.

Medicinal use of cinnamon is currently being touted as beneficial for various ailments. It is important first and foremost to consult a medical professional before taking any supplement, but second to understand which species of cinnamon is being referred to, as they have different properties. The article “Little Bit of Spice for Health, but Which One?” by Laura Johannes in the Wall Street Journal discusses this. Here is an excerpt:
“A recent meta-analysis found cinnamon can lower blood sugar and cholesterol in humans, but so far evidence that it eases arthritis is limited to animal data. For health benefits, cassia cinnamon, which is typically sold in supermarkets, has been more widely studied than Ceylon cinnamon. But scientists say Ceylon cinnamon is likely safer in very high doses than supermarket cinnamon. (….)

“A study published earlier this year in the Journal of Agricultural and Food Chemistry tested cinnamon commercially available in the U.S. and found ‘substantial amounts’ of coumarin, a naturally occurring organic compound that can cause liver damage if consumed in excess. The study found only trace amounts of coumarin in Ceylon cinnamon.

“‘From a safety point of view, Ceylon cinnamon is better,’ says study author Ikhlas A. Khan, assistant director for the National Center for Natural Products Research at the University of Mississippi’s School of Pharmacy in Oxford, Miss. Not everyone is biologically susceptible to the liver damage, he says, adding that cinnamon ‘in moderation’ is safe for everyone.”

An excellent web resource for all things spice-related is Gernot Katzer’s Spice Pages.

On wind-sail pruning

There’s a self-described tree service knocking on doors in my street, trying to get people to pay them to do “wind sail reduction” on their trees. My neighbor just agreed to have them prune 17 of her conifers. Bad idea, right? Can you point me toward resources so I can dissuade her from going ahead with this plan?

Yes. The Washington Department of Natural Resources published an article, “Trees Don’t Wind Sail, Do They?,” in their online newsletter, Ear to the Ground, 12/20/2011. Here is an excerpt:
“Some people claiming to be tree experts will tell you that ‘wind sailing’ is a great way to protect your trees from wind damage. You may have heard this fabricated notion of thinning limbs from trees in order to make them stable during wind storms. This improper pruning technique is promoted to supposedly make trees safer in the wind by allowing wind to pass through the canopy of a tree, thus reducing movement and strain on a tree. Not so!

“This may sound reasonable and may even seem to have some logic behind it. But beware–the truth is, there is no scientific study that shows thinning is wise or safe way to decrease resistance during a wind storm.

“Actually, many studies have shown that the outside limbs can divert some wind from the center of the tree and act as a buffering shield. Aggressive thinning, on the other hand, can make the remaining branches more vulnerable to failure; left isolated, these limbs must take on the elements alone. Pruning out a major portion of a tree’s canopy for the sake of staying upright during a wind storm harms most trees in the long run.”

The DNR has another, similar article from 12/6/2012 in their Tree Link News entitled ‘Windsail Reduction:’ A Northwest Controversy.’

You can also suggest that your neighbor speak to someone at Plant Amnesty, a local organization dedicated to teaching the community about proper pruning techniques (as well as informing them about ill-advised methods!).

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Edible Magnolia flowers

Are Magnolia flowers edible?

Buds, flowers, and leaves in various stages of growth have edible uses. According to the Plants for a Future database, “The flowers [of Magnolia grandiflora] are pickled in some parts of England and are considered to have an exquisite flavor. They are also said to be used as a spice and a condiment.” Cornucopia II by Stephen Facciola (Kampong Publications, 1998) confirms this and also says that the flowerbuds of Magnolia denudata are used in Asian cuisine. After removing the calyxes, the buds are pickled and used to flavor rice, and to scent tea. In Japan, the young leaves and flower buds of Magnolia hypoleuca are broiled and eaten as a vegetable. Older leaves are made into a powder and used as seasoning; dried, whole leaves are placed on a charcoal brazier and filled with miso, leeks, daikon, and shiitake, and broiled. There is a type of miso which is seasoned with Magnolia, hoba miso.

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Seeds and food stamp benefits

I receive a food stamp benefit, and I’ve been able to use it to buy food plants to grow in my garden, but I would like to be able to grow food from seed. Do you know if the benefit covers seeds for food crops?

Thanks for pointing out that food stamp benefits can be used for food plants! I consulted with legal experts at Seattle’s Solid Ground and found out that the benefit does include seeds. Here is the USDA Supplemental Nutrition Assistance Program web-site where this is stated:

Excerpt:
“Households CAN use SNAP benefits to buy: Seeds and plants which produce food for the household to eat.”

According to the historical information on the website of SNAP Gardens, this benefit has existed since 1973, when the Food Stamp Act was amended to include “seeds and plants for use in gardens to produce food for the personal consumption of the eligible household.” You would still need to obtain the seeds from an existing vendor who accepts the food stamp benefit.

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Growing bamboo in Northeastern U.S.

I am considering planting some bamboo in a wet area near the neighbor’s yard. Right now, there are spruce planted in that area. I’m worried the bamboo will edge out the spruce, and I’m worried the bamboo might get into the neighbor’s yard. The species I’m considering is Phyllostachys atrovaginata, which is supposed to do fine in zone 5 (my zone in the Hudson Valley region of New York), and tolerate wet ground. What do you think?

The American Bamboo Society has a useful general article(now archived) on growing bamboo species in the Northeastern U.S. One thing the article says is that there are very few temperate (as opposed to tropical) bamboo species which will do well in wet conditions. Here is another article(now archived) about growing bamboo in Massachusetts, and another article(now archived) about controlling bamboo, which is essential if you plant a running bamboo–especially if it’s planted close to your neighbor’s property!

I do have an idea about how you can plant a running bamboo so that it will not invade your neighbor’s side of the property line, and so it will have improved drainage: what about planting it in a raised bed or container? I’ve seen this done, in a high and long raised bed along a property line, planted with running Phyllostachys.

The species you are interested in, Phyllostachys atrovaginata [also called incense bamboo], is described in an article in American Nurseryman, v.208, n. 7, 2008, as reaching 20-35 feet tall. It does tolerate (or require) moist conditions, as you say. It is hardy to zone 5b, and sustains no winter damage at -5 degrees F but culms will die back at -15 and regenerate new shoots in spring. It is a vigorous spreader, and needs “a width of at least 5 feet to provide a sustainably managed screen or specimen in a lawn. A rhizome access trench (1 foot wide by 1 foot deep, backfilled with sand) provides easy access to the rhizomes for routine inspection and extraction. Inspect three times throughout the growing season. Neglect causes unwanted spread, resulting in a garden thug.” It also prefers full sun, which might not be available in your garden if it is planted in the shade of the spruce trees.

To my reading, this sounds like a lot of work, when it might be easier to plant a hardy clumping bamboo in a container or raised bed–no worries about wet soil, or about invading the neighbor’s garden, and some even tolerate partial shade.

Here is another American Bamboo Society article(now archived) with suggestions for noninvasive clumping bamboo for the Northeast.

Excerpt:
“These plants do not tolerate full sun, but prefer to be understory plants, with overhead canopy above. Cooler, morning sun is acceptable, but hot, midday sun causes the curling of the leaves. Good woody companions are rhododendron, pine, hemlock, leucothoe. Good herbaceous companions are hosta, epimedium, vinca minor, hakonechloa, ceratostigma.”

  • Fargesia nitida – Fountain Bamboo, and its many cultivars nitida ‘de Belder’, ‘McClure’, ‘Nymphenburg’, ‘Wakehurst’: Hardy to minus 20 degrees F – Heights to 18 feet
  • Fargesia murielae – Umbrella Bamboo: Hardy to minus 20 degrees F – Height to 15 feet
  • Fargesia dracocephala: Hardy to minus 10 degrees F – Height to 15 feet
  • Fargesia robusta: Hardy to zero degrees F – Height to 20 feet
  • Fargesia rufa: Hardy to zero degrees F – Height to 10 feet

Invasiveness status of the Tree of Heaven

There seems to be a plant invasion in my Seattle neighborhood. I think what I’ve been seeing are larger specimens of Ailanthus altissima (Tree-of-Heaven) surrounded for many blocks by smaller seedlings of this same tree. It sprouts up through the middle of landscape plants and lawns, and right up against concrete foundations. I feel I should be warning people, but I’d like to know what the local status of this tree is, and I want to be sure I have identified it correctly. I already know it’s aggressive here, and I know it’s been designated invasive in other parts of the U.S. and the world.

You are correct that Ailanthus altissima has quite a track record for invasiveness. As you say, the U.S. Department of Agriculture’s National Invasive Species Information Center lists it. If you want to show people in your neighborhood some clear images of the tree in various stages, the Invasive Plants Atlas of the United States has good information.

If you aren’t completely certain what the plant is, you can bring samples to the Herbarium here at the Center for Urban Horticulture, or you can compare and contrast what you have observed with some close look-alikes:

Tree-of-Heaven is mentioned in a pamphlet on alternatives to invasives for Eastern Washington gardeners, but it has not yet achieved official invasive status. The Washington State Noxious Weed Control Board is considering a nomination to designate it as a Class B noxious weed (second highest priority) for the 2012 state weed list.

You could encourage your neighbors to eradicate it when possible. It spreads by seed (which can be dispersed by birds but especially by wind), and by root sprouts. It is a very fast grower, and it is important, when digging it up, to get every last bit of root, or you will soon find more of it sprouting. The California Invasive Plant Council has excellent, detailed information on its history, its growth and reproductive habits, and several methods of controlling its spread.

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Low maintenance Carex

I am designing a low maintenance landscape. I’m interested in using one of the Carex cultivars that have golden/variegated leaves (Carex dolichostachya ‘Kaga Nishiki’, Carex oshimensis ‘Evergold’, Carex morrowi ‘Ice Dance’, or Carex hachijoensis ‘Evergold’). I would like to use a species that does not need to be cut down each year. Can you advise if any of these would look good all year without cutting back in the winter?

According to The Plant Care Manual by Stefan Buczacki (Crown, 1993), most sedges (such as Carex) require little maintenance. Even those with tall flower stems don’t need staking, and only need their dead flower stems removed in spring, or if damaged by rain or wind. In general, foliage may be trimmed lightly in spring as needed.

Rick Darke’s Encyclopedia of Grasses for Livable Landscapes (Timber, 2007) says that Carex dolichostaya ‘Kaga Nishiki’ will form “a symmetrical fountainlike mound, eventually to 2 feet in diameter. Long-lived and durable, suited for groundcover sweeps. Fully evergreen into Zone 6. Prefers fertile organic soils and light shade or full sun with adequate moisture. Fairly drought-tolerant in shade once established.”

Darke says that Carex hashijoensis is similar to Carex oshimensis but not as cold-hardy. The variegated cultivar you mention, ‘Evergold,’ is actually a cultivar of C. oshimensis, not C. hachijoensis, but there is confusion in the nursery trade.

Carex morrowi ‘Ice Dance’ is described as “strongly rhizomatous but not so fast as to be a nuisance. A superb, self-repairing groundcover.” There are other cultivars, such as C. morrowi ‘Gilt’ (leaf margins cream-white), ‘Gold Band’ (leaf margins cream-yellow), and ‘Variegata’ (a catch-all name for otherwise unnamed variegated selections).

You may find this of interest: Darke’s section on cutting back grasses and sedges states that “most grasses require little maintenance other than being cut back once yearly, and even this is done more for neatness than for the needs of the grass. […] Many evergreen grasses and sedges do not need to be cut back yearly and may grow attractively for a number of years with just minor grooming. Old growth or discolored foliage is often easily removed by gently combing plants by hand.”