Weeds And 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 Covers subjects about horticulture and pest management for the grower and associated industries Florida Nursery Grower Landscape Association Certified Horticulture Professional classes

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.

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.

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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.

“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 .

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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:

Weeds And Seeds

The last post demonstrated the remarkable ability and unique features of aphids that allow them to rapidly boost their numbers and colonize their hosts in favorable conditions. What about weeds? What features give them the ability to rapidly colonize a potted crop or planted field? Many plants become weeds because they have the powerful trick of producing many many seeds. Seeds are dispersed by wind, insects, animals, or by their association with our nursery tools and machinery. Often, these seeds are long-lived in the soil. Consider these statistics:

Probably some unfortunate graduate students or field assistants in 1954 were given the task to count weed seed of hundreds of common weed species from about 50 plant families in North Dakota. The table above is just a sampling (Stevens 1957). In most cases a single plant, judged to be of average size and growing where competition was low, was harvested at maturity or when a maximum number of seeds could be obtained. The plants were air dried for two weeks or more, threshed and cleaned to re-move immature seeds, empty florets, etc. All of the sampling methods are described in the Stevens reference given below.

So basically left on their own, weeds have a profound ability to produce seed. Some seed are not viable, some germinate immediately, and some persist, perhaps for years, in the soil as a “seed bank”. This bank represents the holdings of weed seeds in the soil. Place a “deposit” of seed in this bank, and your “interest” is compounded in a big way. An interesting experiment with velvetleaf (Abutilon theophrasti) an important weed in soybean crops demonstrated this (Hartzler, 1996).

Velvetleaf is a prolific seed producer and seeds are long-lived. In 1990, replicated experimental plots were planted with soybean and then with one of three velvetleaf densities: 0, 0.2, and 0.4 plants per square meter. In subsequent years, the experiments were maintained in a corn-soybean rotation. Weed densities were determined at crop harvest for four years. As seen above– even with competition from the crop plants– velvetleaf density increased dramatically for years following the very sparse initial planting of the weed. There were even some velvetleaf plants seen in the untreated “0” plots, even though the plots were hand weeded to reduce seed production for 5 years prior to initiating the study.

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The number of weed seeds in in the soil can range from near 0 to over 1,000,000 per square yard, and most weed seeds are between 0 and 5 years old. A small number of seed can remain viable for decades or more. With this knowledge, one of the most important principles of weed management is to “never let weeds go to seed”. Never.


Stevens O.A., 1957. Weeds, Vol. 5, No. 1 (Jan.), pp. 46-55

Hartzler R.G. 1996. Velvetleaf (Abutilon theophrasti) Population Dynamics following a Single Year’s Seed Rain

Weeds And Seeds

​H orticulture in Southwest Florida is unlike anywhere in the world. Growing conditions are often ideal. Warm year-round temperatures, generous rainfall, and sunny days encourage plants and people. This microclimate offers a unique palette of foliage, flowers, and fruit.

Enthusiasm about plants is the beginning of being a great horticulturist. Knowledge, effort and experience complete the package. You are most productive and successful when you are familiar with seasons, soils, plant selection, attractive, useful arrangement, insects, diseases, weeds, and many unseen enemies of plant life.

Our objective is to give you a wide exposure to Florida ornamental horticulture, focusing on the southern zone, concentrating on Lee and Collier counties. Our classes are designed to give you useful, local information and to help you to pass the Florida Nursery, Growers and Landscape Association’s (FNGLA) Certified Horticulture Professional tests.


The first class starts this Thursday, August 4th. There are still a few openings but no time to mail in your forms. So just print out the registration form from the next page and bring it along with your payment.

You will enter Naples Botanical Garden on Bayshore Drive and turn on your first right to parking. We will meet in room KC 126.
Signs will be posted.

Feel free to bring your own drinks and snacks as there are no vending machines. This is a non-smoking location.

I will be there at 5:30 to process any registrations and will start the class at 6:00.
See you there!
​Bob Cook FCHP

Plant Identification

In our certification program we are responsible for identifying 259 palms, trees, shrubs, foliage plants, vines, ground covers and bedding plants. This link shows you clear photos , arranged by those categories.

Bob Blog

In this blog I have some horticultural fun. At the bottom of the front page you can choose from categories like; Bedding plant trials, trade shows, salsa recipe, tomatoes, peppers, bad landscaping, garden benches, fairy gardens, poinsettias, and much more.