What is a weed?
Just a plant out of place? Maybe so. "Any plant whose virtues have not been discovered" (Emerson). Maybe. "No more than a flower in disguise" (Lowell). Probably. In nature there is no such thing as a weed. So here we go.
Weeds are classified in several ways, and this is only because everyone is trying to develop some control methods.
Just as with flowers, there are annual, biennial and perennial weeds.
Annual weeds may be summer annuals or, in warmer climates, winter annual weeds.
Biennial weeds will take two years to develop. The first years growth will be near the soil, the second year the weeds will flower, produce seed, and then die. An example is wild carrot, better known as Queen Anne's Lace.
And lastly, the perennial weed has parts known as tubers or rhizomes. They will live an indefinite number of years in undisturbed areas. They can be in the soil for forty years! Studies have shown that curly dock and common mullien will germinate after 70 years. Yikes!
Why even bother naming weeds? It is the eradication most people are interested in. When herbicides are used, some chemicals are developed to be very specific. Commercial growers are most concerned.
But by merely cultivating, plowing, or mulching, one can eliminate or control most weeds in the garden or flower bed.
It is still important to be able to recognize certain weeds such as poison ivy, poison oak, poison sumac, or horse nettle (pictured above). At times they make for very unpleasant personal conditions.
Visit the Weed Science Society of America at http://www.wssa.net
You might also want to look at New Jersey Weed Gallery
(If you would like to read this in Danish, go here.)
"If dandelions were rare and fragile, people would knock themselves out to pay $14.95 a plant, raise them by hand in greenhouses, and form dandelion societies and all that. But, they are everywhere and don't need us and kind of do what they please. So we call them weeds and murder them at every opportunity".....Robert Fulgham.