Beneficial Weeds

A beneficial weed is any of various plants not generally considered domesticated, but which nonetheless has some companion plant effect, or else is edible or somehow beneficial. Beneficial weeds include a great many wildflowers, as well as other weeds that are commonly removed or poisoned.

Although errantly assumed to compete with neighboring plants for food and moisture, some "weeds" provide the soil with nutrients, either directly or indirectly.

For example, legumes, such as white clover, add nitrogen to the soil through the process of nitrogen fixation, where bacteria symbiotically living in their roots extract nitrogen from the atmosphere, making it accessible in the soil for its host, and any nearby plants.  Clover attracts earthworms by the gazillions, and we all know how beneficial earthworms are for the health of the soil and the plants that grow in and on it.

Others use deep tap roots to bring up nutrients and moisture from beyond the range of normal plants, so that the soil improves in quality over generations of that plant's presence.

Weeds with strong, widespread roots also introduce organic matter to the earth in the form of those roots, turning hard, dense clay dirt into richer, more fertile soil.In fact, some common plants like tomatoes and corn will literally "piggyback" on nearby weeds, allowing their relatively weak root systems to go deeper than they could have alone.

Many weeds protect nearby plants from insect pests.  One way they can do this is to repel insects and other pests through their smell, as do alliums and wormwood.  Another is to entirely mask a companion's scent, or the pheromones of pest insects, as with ground ivy and wild oregano.  Some also are unpleasant to small animals, because of their spines or other features, keeping them away from an area to be protected.

Some weeds act as trap crops, distracting pests away from valued plants. Insects seeking a food plant search by smell, and then land at random on anything green in the area of the scent.  If they land on an edible "weed", they will stay there instead of going on to the intended victim. Sometimes, they actively prefer the trap crop.

Plants such as ryegrass, red clover, and white clover act as living mulches, by inhibiting the growth of any weeds that are actually harmful, and creating a humid, cooler microclimate around nearby plants, stabilizing soil moisture more than they consume it for themselves.

A common companion plant benefit from many weeds is to attract, or be inhabited by, beneficial insects or other organisms which benefit plants.  For example, wild umbellifers attract predatory wasps and flies that eat nectar, but reproduce by feeding common garden pests to their offspring.  Some weeds attract ladybugs or "good" types of nematode and provide ground cover for predatory beetles.

There is much more information on this subject and I suggest that  everyone do their own research, as the subject is very interesting and enlightening.  I have worked along side other gardeners who are quite anal about weeding, and others who are more laid back to their approach.  Both harvest lovely produce.  Personally, I'm for doing the least amount of hard labor if it gets me the same results.  Why waste time and energy when you could be doing something more constructive, like sitting back and enjoying your garden?



Sources:

Wikipedia:  http://en.wikipedia.org/wiki/Beneficial_weed