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Keller: What Weeds Really Are

on November 16, 2017 - 8:48am
By CHICK KELLER, Curator
Jemez Mountains Herbarium
 
In response to a resent letter to the editor (link) with questions about weeds and what to do about them, here are some answers:

First – a weed to me is any group of plants growing where you don’t want them, or crowding out other more desirable plants.

Second – not all weeds are invaders from other places. Most are natives.

Third – these are very important plants for restoring disturbed areas. I call them nature’s “first responders”. They are almost all annuals (must grow from seeds each year as last year’s die and don’t come back).

Their job is to grow in disturbed areas—from flooding, forest fires or other disturbances-usually human caused.

These areas have had their rich, layered, undisturbed, fertile, and absorbent soils destroyed leaving muddy, poor and mixed, easily eroded soils that most native plants won’t grow in.

As annuals, they die and put their vegetal material down on the ground, both enriching it and guarding against erosion. They are the first to help recovery.

BUT, and here comes the rub, because they are annuals, they must insure next year’s crop and so develop thousands of seeds, which, when they germinate, often fill the land with sometimes dense stands of plants.  

Fourth – These plants won’t grow in undisturbed soil and so often present no problem for ecology. It is like magic when one walks from disturbed, weed-filled areas into undisturbed ones. The plants change species immediately.

One of the homeowner’s problems is that our carefully designed gardens are in fact disturbed soil (although we have put in some enrichments). And so nature’s first responders “think” they are needed to help out and they fill our gardens with unwanted growths.

Fifth--most of these “weeds” are native. Here are some examples:  sunflowers, purple asters, yellow greenthread, blanketflower, yellow and white sweet clover, wild morning glory, yellow evening primrose, wild chrysanthemum, lambs' quarters, amaranths, spurges, etc. Most of these are desirable for their color and/or edibility. Birds love many of them.

However, some natives are not desired—prickly lettuce, less common thorny ambrosias, and wild cosmos (with its seeds that stick to your clothes). Tall yellow mustards can be a problem but sometimes not. Perhaps the worst is New Mexico Locust—a small shrub/tree covered with nasty thorns. It has invaded many areas where forest fire destroyed all but it and the oaks, making hiking sometimes painful not to mention torn clothing. Other natives occur in such small numbers that they are actually desired.

Sixth – Some however, are non-native and very troublesome such as cheatgrass, Russian thistle (tumbleweed--not a real thistle), summer cypress (Kochia), musk and Canada thistles, viper grass (dandelion lookalike), Russian and spotted knapweed—all nonnative, often quite invasive and damaging to native plants. Bull Thistles are sometimes a problem but mostly not. In addition, we have a number of native thistles some of which look pretty much like bull thistles and should not be ‘weeded'. Before you start cutting down thistles, it’s important to learn how to tell them apart. Tall stalks of mullein can be quite numerous but usually aren’t a problem. Finally, there is that bane of every gardener’s life—bindweed.

To kill with pesticides or not.

In my experience, carefully, constant weeding does the trick and no chemicals are needed. However, I got a dense infestation of curly dock and after three years of digging, cutting, etc. I carefully sprayed Roundup on their leaves. The result was gratifying—they died, but other plants nearby did not. Perhaps the key here is careful application not the broadcast spreading done so often.

What to tell the County or better, how to help them out. First point out that every place they disturb will be ‘theirs to care for forever”. So, if they wish to reduce their weeding problems, they should be very careful what they disturb. In fact, mowing often destroys wonderful flowering areas such as at the airport where greenthread blooms in beautiful masses only to be destroyed by well-meaning mowers.

PEEC is a resource We know the plants -- which are problems and which are not and are willing to go out with County people to discuss what should be done.

I recommend a wonderful book for those who are interested in further study—a great name, Weeds of the West. PEEC has it.


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