Weeds With Seeds

Wildflower seed mixes full of weeds Lorraine Brooks waters flats filled with wildflowers grown in the Center for Urban Horticulture greenhouse. Her advisor Sarah Reichard said it was the most Weed seeds are among the most patient organisms in nature. Many weeds can produce thousands of seeds per plant per year, and those seeds might lie dormant for decades, just waiting for the right conditions to sprout.

Wildflower seed mixes full of weeds

Lorraine Brooks waters flats filled with wildflowers grown in the Center for Urban Horticulture greenhouse. Her advisor Sarah Reichard said it was the most beautiful-looking experiment ever done there.

The seed packets have labels with romantic-sounding names such as meadow mixture and wedding wildflowers, while others tout backyard biodiversity and make reference to Earth Day. When growing 19 such packets of wildflower mixes, however, UW researchers found that each contained from three to 13 invasive species and eight had seeds for plants considered noxious weeds in at least one U.S. state or Canadian province.

And what makes it nearly impossible for gardeners who want to be conscientious is that a third of the packets listed no contents and a little more than another third had inaccurate lists. Only five of the 19 correctly itemized everything.

“I can’t recommend using any wildflower seed mixes,” says Lorraine Brooks, who did the work at the UW’s Center for Urban Horticulture while earning her bachelor’s degree.

Brooks found the least unruly of the wildflower mixes was a packet in which only 30, or 28 percent, of the 106 plants that sprouted and produced flowers were invasive. Among the worst was a mix in which 100 percent of what flowered was invasive. There were 200 plants of only three species in that packet, which was labeled “native.” Of the three species, only one is believed to be native to the Pacific Northwest and it represented just 1 percent of the mix. Two other mixes contained not one but two noxious weed species.

Brooks and Sarah Reichard, UW assistant professor of forest resources, said gardeners are better off using their favorite plants, or seeds for their favorites, in order to control what’s grown in their yards.

In Washington, the state and 49 local weed control boards maintain lists of invasive species and noxious weeds. Depending on how serious a threat is posed by a species and how widespread it already is, weed managers may prohibit its sale and demand landowners eliminate it. Other species fall into categories in which landowners are asked to prevent the plant from going to seed so it can’t spread.

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Gardeners might be surprised at the number of flowers that are readily available for sale and use that are considered invasive or noxious. For instance the wildflower most commonly observed as part of the mixes was the popular bachelor’s button (Centaurea cyanus), germinating in beautiful hues of pink and blue from three-quarters of the packets tested. Bachelor’s button might be fine if kept confined to one’s own yard but it’s invasive — that is, it outcompetes other plants — when it gets into native grasslands and prairies.

It hasn’t been named a noxious weed but it is on the state’s “education list” in the hope that property owners will become knowledgeable about the risks of growing it, says Reichard, who serves on the committee that considers changes proposed for the state’s list.

Yellow toadflax (Linaria vulgaris), on the other hand, is listed as a noxious weed in Washington, Oregon, Idaho and 11 other states and provinces. Colorado, for example, classifies it among the top-10 prioritized noxious-weed species, those that are most widespread and cause the greatest impact.

With yellow flowers tinged with orange that resemble snapdragon blossoms, toadflax was found in four of the wildflower mixes. Only one listed it. All four of the mixes are produced in King County where the plant is a “principal weed for control,” an even stronger designation than the state’s listing of it as a Class C noxious weed.

Even labels that refer to wildflowers as native should be avoided because everything is native to someplace, but that place may not be where you live, Reichard says. Just think about the differences in plants between Eastern and Western Washington, she says.

The 19 packets tested were produced by Burpee, Ed Hume, Lake Valley Seed, Lilly Miller, Molbak’s, Napa Valley Wildflower, Nature’s Garden Seed Co., and Sundance. Seventeen were purchased and two were gift items, including one from the World Wildlife Fund (WWF).

Handed out as fund raising thank-yous by the WWF and other environmental and charitable groups, and bearing labels that refer to pastures, meadows and native flowers, these mixes may even make people think they are suitable for areas next to woodlands, fields or prairies, Brooks says.

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“But that would be a big mistake.”

A wild, wild world

As a UW undergraduate research project, Lorraine Brooks grew the contents of 19 different packets of wildflower mixes for 24 weeks. She was able to identify 84 species.

Four of the species are listed as noxious weeds in at least one state or Canadian province, as well as being considered invasive. They were common yarrow, Achillea millefolium ; dame’s rocket, Hesperis matronalis ; redroot pigweed, Amaranthus retroflexus ; and yellow toadflax, Linaria vulgaris .

Thirty-five others are listed as invasive and included baby’s breath, Gypsophila elegans ; bachelor’s buttons, Centaurea cyanu ; Black-eyed Susan, Rudbeckia hirta ; blue flax, Linum perenne ; California poppy, Eschscholzia californica ; cosmos, Cosmos bipinnatus ; cow cockle, Vaccaria hispanica ; crimson clover, Trifolium incarnatum ; forget-me-not, Myositis sylvatica ; poor man’s weatherglass, Anagallis arvensis ; wild lupin, Lupinus perennis ; doubtful knight’s spur, Consolida ajacis ; and Mexican hat, Ratibida columnifera .

Weeds on the Web

Check out Washington’s noxious weeds at http://www.wa.gov/agr/weedboard/ and Western invasive species at http://invader.dbs.umt.edu/.

For information specific to King, Pierce and Snohomish counties try:

Controlling weeds starts with the seeds

Gardeners should learn to look for them in ‘seed banks’

Weed seeds are among the most patient organisms in nature. Many weeds can produce thousands of seeds per plant per year, and those seeds might lie dormant for decades, just waiting for the right conditions to sprout.

If you want to control weeds, then find where these seeds accumulate — in “seed banks.”

“Gardeners should care because that’s where all their seeds are coming from,” said Ed Peachey, a weed science specialist with Oregon State University Extension. “If you don’t prevent weeds from producing seeds, then you’ll wind up with large seed banks, and always fighting with the weeds that emerge from those seed banks.”

Weeds are unwanted because they are considered unattractive in manicured yards, they spread quickly, and they muscle aside desirable plants from life-giving sunlight, nutrients and moisture.

“Understand what you have in your garden and then decide what to get rid of,” Peachey said. “Some weeds are incredibly well adapted to gardens and they compete.”

Weed seeds or banks accumulate in neglected lawns, near downspouts and shaded areas, around pathways and driveways, in newly cultivated ground — even under decks, despite the scarcity of sunlight.

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Weeds have a number of things in common, said Sandra Mason, an extension horticulturist with University of Illinois Extension.

“They go through their life cycle rapidly, flower quickly, produce vast quantities of seeds, and have some seed adaptations for travel by wind, water or animals,” Mason said in a fact sheet.

Soil movement and changes in water content invigorate annual seeds, Peachey said. “Most weed seeds don’t live particularly long, a few years perhaps. But there always are a few that can linger.”

A dandelion may produce 15,000 seeds per year, purslane more than 52,000, while pigweed can leave behind over 117,000, according to Colorado State University Extension horticulturists. Purslane and pigweed seeds can persist in the soil for 20 and 40 years respectively, they said.

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One Arctic plant was germinated after its seeds lay frozen for 32,000 years in the Siberian tundra, said Russian scientists who used radiocarbon dating to validate their claim.

Weed management options are many and varied.

“Hand-weed in small spaces,” Peachey said. “Use organic mulches to keep weeds from emerging and producing seeds later. Create stale seed banks by disturbing the soil, using a flaming tool to burn off whatever weeds sprout up, and then do your planting.”

It takes two or three weeks for seeds to emerge though, so that scorched-earth policy may delay spring gardening.

“Use specialized hoes,” Peachey said. “Triangular hoes or hoop hoes are good at getting the entire weed root out.”

Peachey doesn’t recommend using chemicals in vegetable gardens unless you’re working with more than a tenth of an acre. “Very few (chemicals) that are labeled for garden use are practical,” he said.

Note: When weeds make seeds, they make them fast.

“It’s important to watch weeds through the entire summer season,” Peachey said. “If some get by, and if you can’t dig them out, then at least cut off their seed heads. It’s cheaper to get rid of the seeds than it is to fight the weeds.”