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The Garden Plot for November 30, 2007
3:55 PM - 4:00 PM
[Program Website]
Today's Highlight: "Cheatgrass"
There’s no denying that winter is now here. Most plants are completely devoid of green this time of year. But not Cheatgrass. Like most pushy weeds, this grass (that plagues us with millions of scratchy seedheads clinging to socks and pantlegs in July) is sneaky. Cheatgrass (Bromus tectorum) can be found around Western Montana now as a 1-2 inch green carpet in open, disturbed garden, pasture, and native areas. It is a short, hairy-leaved grass and will be one of the first plants to green up this coming spring. It germinates in the early spring as well as in the fall. Then, it patiently waits out the winter, ready to take off with the first temperatures above 32 F. By early spring, it’s already way ahead of plants that wait until spring to germinate and require warmer temperatures to grow.
If Cheatgrass provides an extended green period in the fall and a lush-looking early spring, why is it such a problem? Even if you could get past all those summer seeds with prickly awns that end up in clothing, Cheatgrass is a problem because it displaces native vegetation. It out-competes native grass and shrub seedlings for soil moisture. Cheatgrass also changes the frequency, extent, and timing of wildfire. It’s early-maturing, highly flammable, summer-dry foliage increases the chance of ignition and spread of wildfire.
Cheatgrass is particularly invasive because it is drought tolerant, but can tolerate moderate moisture. It can also grow in almost any type of soil, including eroded and low nutrient soil. Cheatgrass likes wet, moderately warm fall seasons. That’s why it did so well this fall. The only thing it doesn’t like is hot temperatures. It stops growing when temperatures exceed 60 F. Cheatgrass is an annual weed and establishes ONLY by seed. But it has tremendous seed production potential, up to 300 seeds per plant! Worse yet, all these seeds DO NOT germinate all at once. Instead, as many as 50% of the seed produced can remain dormant in the soil for 2-3 years. Dormant seeds can withstand extremely high soil temperatures and thus seed viability is not decreased by burning pure stands of Cheatgrass. However, some researchers report that late spring burning of a mixed-shrub-cheatgrass stand might generate temperatures high enough to kill most Cheatgrass seeds. They also recommend prompt revegetation immediately after burning. Cheatgrass seedling emergence is greatly curtailed when seeds are buried at least 4 inches below the soil surface. In small-scale infested areas, deep tillage and thick mulches might be one way to manage a Cheatgrass infestation.
Other ways to reduce Cheatgrass infestation include spring tillage and mowing within one week of flowering in early summer. The timing of mowing is key. If you mow too early, Cheatgrass will re-grow and flower again. If you mow too late, viable seeds may have already formed. In one study, repeated mowing (every 3 weeks), effectively controlled Cheatgrass seed production that year. Moderate spring and fall grazing may significantly reduce Cheatgrass plant numbers, but heavy grazing can enhance Cheatgrass invasion.
Bare soil invites Cheatgrass. The longer soil is plant-free, the greater the chance of invasion. Plants help keep Cheatgrass out of open areas, pastures, landscapes, gardens, orchards, and berry patches. Choose perennials that shade the ground and fill above, and below ground, spaces rapidly.
Least-toxic option, non-selective herbicides, such as vinegar, can reduce Cheatgrass if applied when Cheatgrass seedlings first germinate in the fall or early spring. For more information on newer herbicides being tested for selective Cheatgrass control, call your local weed district office or Extension service office.
Helen Atthowe's new short program of gardening tips
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