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Elisabeth C. Miller Library

Keyword: Invasive plants

Water chestnuts and edible tubers

What is the botanical name for water chestnut? Will it grow here? Are there other water plants that have edible tubers which will thrive in the Pacific Northwest? What about edible lotus root, from Chinese lotus?

 

Chinese or Sacred lotus (Nelumbo nucifera) is hardy in zones 4-10 and is considered invasive in some parts of parts of the midwestern and southeastern U.S. This article in The Guardian by Mark Griffiths, author of The Lotus Quest, suggests growing it in a container in a conservatory or on a sunny deck. However, you may not want to harvest tubers from a lotus grown in a relatively small container, as the plant needs to be large enough to have a substantial system of linear growth in order to sacrifice some of its tubers for human consumption. According to the Colorado Water Garden Society, “Lotus grow in a linear fashion, with a sequence of a tuber producing a leaf and perhaps a flower, then beginning another tuber to repeat the cycle . . . Tuber, leaf, flower, tuber, leaf, flower, etc. Each terminal point produces a single leaf and flower and then sends out the next, new growth. Beneath the soil, lotus growth takes on one of two forms: runners and tubers. The Summer “runner” growth is thin and long (to 24″+).”

American yellow lotus (Nelumbo lutea) also has edible tubers, but it can be an aggressive grower. If you are seeking out plants, be aware that there is sometimes identity confusion among Nelumbo, Nymphaea, Nymphoides, and Nuphar. In King County, there are two common invasive water lilies that are sometimes mistaken for lotuses, Nymphaea odorata and Nymphoides peltata. While some of these water lilies have tubers that have been considered edible in times of famine, they are not a desirable food source.

The common name ‘water chestnut’ may refer to the edible corms of the Chinese water chestnut familiar from Asian cuisine (Eleocharis dulcis), which is in the sedge family (Cyperaceae), or to European water chestnut (Trapa natans), which is in the loosestrife family (Lythraceae). Eleocharis is not winter-hardy in our area (it requires zones 9-11). Trapa natans is a noxious weed in Oregon and is on the Washington State Noxious Weed quarantine list, so it is not a good choice if you are planning to grow your own aquatic plants. Green Deane’s Eat the Weeds webpage describes the differences between these plants.

One commonly grown native plant with edible tubers is Sagittaria latifolia (common arrowhead, wapato, duck potato). It is an attractive ornamental in a water garden. According to Missouri Botanical Garden, the starchy golf-ball sized tubers that develop at the ends of the rhizomes (underground runners) “are edible, and may be boiled or baked and eaten as a potato-like food. Native Americans harvested and consumed these tubers, which in some areas were known as wapato. The tubers are also an important food source for waterfowl, hence the name duck potato.” According to Eat the Weeds, only Sagittaria latifolia is of edible interest to humans because the size of the tubers or corms is more significant than in other species. Generally, the larger the leaf size, the larger the edible tuber. In any case, avoid planting the two species of Sagittaria on the Washington State Noxious Weed list: S. platyphylla (quarantine list) and S. graminea (class B).

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Paterson’s curse

What can you tell me about Paterson’s curse? It’s a weedy plant with blue flowers mentioned in an Australian novel about an Aboriginal community and their ongoing struggle with the effects of colonization.

 

Paterson’s curse is a common name for Echium plantagineum, also known as Salvation Jane, purple viper’s bugloss, Lady Campbell weed, blueweed, and Riverina bluebell. It is invasive in Australia, where it has overtaken pasture land. It is toxic to horses and other grazing livestock. (There is a similar plant, Echium vulgare, which is invasive in Washington State.)

The source of the name is said to come from the Patterson family (the plant dropped the second T through common usage over time) who introduced it to their garden in Cumberoona, New South Wales around 1880. However, according to Australian author Roger Spencer, the plant’s presence was first recorded in Australia in 1843, in the garden of John Macarthur, near Sydney. It began appearing in nursery catalogues by 1845, and by 1890 it was entrenched in New South Wales and South Australia.

There are two theories about the name Salvation Jane. In times of drought, when native pasture plants died back, Echium plantagineum was seen as a ‘salvation’ because it grew when nothing else would. The hooded shape of the flowers call to mind the bonnets of 19th century Salvation Army missionaries.

You might be interested in reading more about indigenous Australian uses of plants that predate colonization.

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Center for Invasive Species Plant Management

The Center for Invasive Species Management (CISM) developed an online Restoration Resource Database to allow land managers to search for literature, books, handbooks, and web sites on restoration, particularly related to invasive species. CISM is by June 2015 no longer in operation, and the website now serves as an archive of the agency’s projects and resources.

On propagating Paulownia

How can I propagate a Paulownia tree?

 

Something to consider before propagating this tree is its invasive potential. Depending on your location, increasing the population of Paulownia trees may not be wise. The U.S. Department of Agriculture lists Paulownia tomentosa as an invasive species. If you are in King County in Washington State, you may be interested to know that the Center for Invasive Species shows this tree in its Early Detection and Distribution map.

Nevertheless, directions for propagation are available. Peter Thompson’s book, Creative Propagation (2nd edition, Timber Press, 2005), states that Paulownia is best propagated by seed in the spring, or by semi-mature root cuttings laid horizontally just below the surface of the soil. I suggest that you think twice before propagating this tree.

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Spread of Ranunculus ficaria

Can you tell me about the spread of Ranunculus ficaria ‘Green Petal’?

 

The Royal Horticultural Society’s A-Z Encyclopedia of Garden Plants (ed. Christopher Brickell; DK Publishing, 1996) indicates that Ranunculus ficaria (now known as Ficaria verna) spreads a foot or more, but the following information, from a local gardener (Paghat) who grows several cultivars of this plant, suggests that “more” may be quite a bit more. Excerpt: Due to their being potentially invasive, we placed them where it would not matter, but might even be rather nice, if they spread a great deal.

The species is considered invasive, as these sites indicate:

From the Urban Ecology Center

From the USDA site.

It is possible the cultivar is less invasive than the species, but I would certainly keep an eye on it.

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Training goji berry vines

I am growing goji berry plants in my garden. I was hoping their growth habit would be more upright but they are sprawling wildly. Do you have suggestions for training them? Should I be concerned that they might become invasive?

 

Susanna Lyle’s book Fruit & Nuts (Timber Press, 2006) says these shrubby vines are short-lived, peaking in berry production at about 5 years of age and typically living for 8 years or so. She advises planting them near a fence or trellis so that they can be trained up it; some sprawling is to be expected. Utah State University Extension’s October 2015 article, “Goji in the Garden,” offers general cultural information (while mentioning that the plant is a weed in some areas).

Lycium barbarum (goji, also called wolfberry and boxthorn) can be invasive (or at least aggressive) in some areas. An article by Vern Nelson in The Oregonian (August 17, 2008) mentions this tendency, and suggests containing them in a 4 by 5-foot square support structure. Be aware that “wolfberries take root wherever they touch the ground.” This is worth bearing in mind, as is the fact that Lyle’s book says “the extensive root system can help stabilize banks,” which one could interpret to mean that removing unwanted plants might be a fair bit of work!

Suckering roots are only one way the plant spreads; seeds are another. Goji berry (boxthorn) is the “Plant of the Month” in the Whatcom County Master Gardeners Weeder’s Digest from August 2006. Author Cheryll Greenwood Kinsley notes that when the plant was first introduced in Europe, people weren’t enamored of the fruit but birds were, and now “the shrub has naturalized in Britain and is listed as a noxious weed on two continents and in at least some parts of several states, including Montana and Wyoming.” She recommends keeping the birds away from it to discourage its spread.

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Plant division and propagation

I am wondering if the following plants can be divided or propagated successfully: Heuchera, Donkey Tail Spurge (Euphorbia), Corsican Hellebore, and Helianthemum.

I consulted The American Horticultural Society Plant Propagation book,
edited by Alan Toogood (DK Publishing, 1999), and it says the following:

  1. Heuchera: by division or by seed in spring. Since cultivars may not
    come true from seed, I would recommend dividing your plants. Once spring
    growth has begun, lift the plant from the ground and remove small
    sections from around the edge (look for good roots, and 2-3 shoots).
  2. Euphorbia myrsinites: (Just a note: based on the USDA information that
    this plant is invasive in Oregon and banned in Colorado, I would think twice before propagating it. This species does a fine job of propagating itself, apparently. In general, the genus Euphorbia can be propagated by division in early
    spring, or from spring to summer, by seeds in fall or spring, and by cuttings in summer or fall, but if you were to propagate by cuttings, you would need to protect your skin from the sap.
  3. Helleborus argutifolius can be propagated by division after flowering,
    or by seeds in summer. Test seed capsules for readiness by gently
    squeezing. If the seed capsule splits to reveal dark seeds, it is ready
    for harvest. Wear gloves! H. argutifolius (Corsican hellebore) often
    self-seeds. Check around the base of the plant in spring. When each
    seedling has at least one true leaf, gently lift and transplant to moist,
    fertile soil in light shade.
  4. Helianthemum can be started from greenwood cuttings rooted in summer
    and fall, and by seeds sown in spring in a frost-free location.

If you would like further information on the relative ease or difficulty
of each of these methods for each of these plants, I recommend coming to
the Miller Library and looking at our books and other resources on
propagation. Here is a link to a booklist.

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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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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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on the invasiveness of Bear’s breeches

I am wondering how invasive bear’s breeches is? I have heard it can be invasive in the Northwest. Will I be battling roots or suckers constantly? Can it take over any plants near it?

 

Acanthus mollis, or Bear’s breeches, is not listed as noxious in King County, Washington State, or on the federal list of noxious plants. This is not the same as saying it isn’t potentially aggressive, although I’ve never heard about it being a serious problem here. It is considered invasive in parts of Australia, though.

The Plants for a Future database offers the following information on this plant and its growing habits:
“Plants can become invasive, spreading by suckers, and they are difficult to eradicate due to their deep roots.”

According to the Pacific Northwest site, Rainyside Gardeners, it is sometimes difficult to get this plant to bloom. A Washington State University Extension site says that Acanthus mollis is potentially invasive in climates warmer than ours.
“This species is classified as a groundcover in that any pieces of root cut from the original plant can easily contribute to further plant spread.”

If you want to grow it but are concerned about it spreading, you could try containing the roots with an 8-inch root barrier (similar to what is used to keep running bamboo in check). On the other hand, if you have this plant and decide that you wish to be rid of it, the book Wildly Successful Plants: Northern California Gardens by Pam Peirce and David Goldberg (Sasquatch Books, 2004) says that removing every bit of root over two or three seasons of growth should get rid of the plant. If you cannot eradicate it by continually digging up each new shoot, you may have some luck using a flame weeder (with due caution and appropriate protection). Northwest Center for Alternatives to Pesticides describes how to use this tool.