What makes weeds so successful
What Makes Weeds So Successful?
Susan Donaldson, University of Nevada Cooperative Extension
Did you ever wonder why one plant is a weed, and another a valued flower? It’s all a matter of opinion,
really. The common definition of a weed is that it is “a plant growing where it’s not wanted.” The worst
weeds share some common characteristics, however, and we can agree on hating them.
Invasive weeds are hard to control, grow quickly and vigorously in poor soils, and tend to take over sites
so quickly you’d swear they multiplied overnight. Some have spines or burs that interfere with
recreation; others are incredibly flammable or provide ideal habitat for the growth of pests like
mosquitoes. Invasive weeds steal our water, damage water quality and reduce property value. Invasive
species have contributed directly to the decline of 42 percent of the threatened and endangered animal
species in the United States! Let’s also not forget how expensive it can be to try to control them.
Often the seemingly overnight growth of these undesirable plants can be attributed to one of the
• Weeds have the ability to grow under a wide range of conditions. Let’s face it: weeds grow
anywhere, including in cracks in the asphalt, in parched, salty, disturbed or compacted soils and
even through concrete. Last summer, I observed puncturevine (Tribulus terrestris
) growing along
the shoulder of a road. The ground was so hard and dry, I could hardly push in a shovel to dig
out the plants. They were flowering profusely, however.
• Weeds have prolific seed production or can spread via roots and other plant parts. A local
example is tall whitetop (Lepidium latifolium
). It not only produces thousands of tiny seeds, but
also spreads by creeping roots. If you cut or fragment the root by pulling or attempting to dig
out the plant, each pieces that remains in the soil can grow into new plants. So, if you pull one,
• Weeds have the ability to sprout earlier and grow faster than native or desirable plants.
Cheatgrass (Bromus tectorum
) is a great example of this characteristic. It’s what’s called a winter
annual, sprouting in the fall or early winter after we get some rainfall or early snowmelt. It stays
alive during the winter, lurking under the snow. It will grow and reproduce before other plants
What does this mean for you as a weed manager? You need to be constantly vigilant, inspecting your
property on a regular basis for the first signs of weed invasion. When you see what appear to be weeds,
bring a sample to us at University of Nevada Cooperative Extension, 4955 Energy Way in Reno, and we’ll
identify it for free. Once you know what it is, we can design a management plan that works for you.
Timing is really important when managing weeds. If you wait until the plants have flowered and set seed
(or made painful burs) it’s too late! To be effective, weeds must be managed before they reproduce.
Fight the urge to manage the weeds by bulldozing or blading large areas. Think about it –: what’s the
first thing you see growing on a newly excavated vacant lot? Weeds! In spring, mustards make their
appearance, followed by Russian thistle (tumbleweeds) in the summer when the soil warms up. If you
avoid disturbing the soil and encourage vigorous, healthy vegetation to cover your soil, you’ll have fewer
Another common practice that results in rampant weed growth is the use of contaminated fill material
such as top soil or gravel. Depending on the source, these materials may contain some of the worst
weeds – thistles, tall whitetop, puncturevine, and more. Whenever possible, purchase these materials
from reputable sources or inspect the source.
The more proactive you are, the easier it will be to manage your weeds. Good luck and happy weed
You can help in the fight against invasive weeds. Learn to identify them by going to Be on the lookout constantly, and report them when found. Learn which are ok to pull, and which need additional treatment to kill the roots. Become a weed warrior!
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