Non-Toxic Weed Control
Much of this information comes from Golden Gate Gardening by Pam Peirce. This is a great book for Bay Area gardening with an extensive section on dealing with weeds. Another great book and source is The Gardener’s Guide to Common-Sense Pest Control by Olkowski, et al.
Beneficial Uses of Weeds
- Eat them. Some weeds are edible, and are great in salads
or as greens. Learn to recognize them! (Try dandelions, chickweed,
dock, epazote, Himalayan blackberry, lambsquarters, miner’s
lettuce, mint, mustard, nasturtium, New Zealand spinach, onion
lily, purslane, shepherds-purse, sorrel, wild radish.)
- Compost them. Most weeds can be used to make compost, or
they can be dug into the soil as a green manure. Many weeds can
be left on the soil surface after cutting, to serve as mulch and
to feed earthworms and other soil organisms. (Try chickweed especially.)
- Attract beneficial insects. Many weeds also provide pollen
for bees and serve as a refuge for certain beneficial insects.
(Try mustard, wild radish, pigweed, white sweet clover.)
- Improve your soil. Some deep-rooted weeds open up the subsoil to water and to the roots of more delicate plants. You can use deep divers to improve your soil. (Try lambsquarter, sowthistle, vetch, wild chicory, plantain, purslane, nightshade.)
Weed Control
For weeds, there are no environmentally safe miracle cures that come in bottles. Weed control can be achieved through a combination of planting techniques, mulching, hand pulling, hoeing and prevention. Here are some suggestions.
- Mulch. To get weeds under control, try sheet mulching.
Put down newspaper or corrugated cardboard 1-2 inches thick. Cover
with 2-4 inches of straw, leaves or woodchips if desired. Keep
the mulched area moderately moist. This can be especially effective
against hard-to-control weeds by blocking out light and not allowing
weeds to penetrate. (Mulching also holds in soil moisture, reducing
the need for watering.) Avoid using plastic sheeting, because
it blocks out air and kills the beneficial organisms in your soil
that keep it healthy.
After a plot has been weeded, a 4-inch thick organic mulch helps control weeds by inhibiting the germination of weed seeds beneath the mulch. Furthermore, any weeds rooted in the loose mulching material are easier to pull. Prunings, leaves and other green waste can be used as mulch. Bark, straw and sawdust make good mulch as well.
- Hoe and hand-pull. It is most important to weed an area
during the first six weeks after you plant, so that your young
crops don’t have to compete with the weeds. Hand-pulling
will become easier as you learn the habits of various weeds and
how to pull them. Be especially sure to cut weeds down before
they go to seed.
Perennial weeds store their energy in their roots. A tactic for dealing with them is to cut down the tops of the weeds, let them grow back until they begin to sprout, then cut them back again. Repeat this until all of the energy is drawn out of the roots.
- Plant densely. Space your plants close enough together
so that the leaves of adjoining plants touch at maturity. Try
competitive planting; quick-growing annuals, vigorous ground covers,
and plants with dense foliage can shade the ground enough that
weed seeds have difficulty germinating. Also, trees and shrubs
can be used for shade so that weeds will not grow.
- Replant with native plants. Natives are very hardy, and
compete well with weeds. (Many are also drought tolerant!)
- Provide excellent growing conditions. Provide your crop
with loose and fertile soil, adequate water, and proper sunlight,
so that it can compete with the weeds.
- Monitor inputs. Avoid new infestations by watching what
you introduce into your garden. Some compost and dirt contains
weed seeds.
- Use allelopathic cover crops and companion planting. As
some plants grow, they release biochemicals that either suppress
or encourage the plants growing around them. Good allelopathic
crops to suppress weeds are rye, buckwheat, black mustard and
sorghum-sudangrass hybrids. Companion planting in your vegetable
garden can also be used to control weeds. For example, growing
squash with corn helps suppress weeds.
- Pre-sprout. To get rid of annual weeds, try presprouting:
dig, amend and rake your soil. Water as if you had sown crop seeds.
After the weeds start to sprout, hoe, just scraping the soil surface.
Don’t dig further because this will stimulate seeds that
are deeper in the soil to sprout. If the plot is particularly
weedy, repeat this process.
Herbicidal Products
Weeds develop resistance to herbicides over time. Herbicides kill beneficial organisms and pollinators in your garden as well as contaminate our waterways, soil and food. For these reasons, the usual herbicides should be completely avoided and least-toxic herbicides should be used only on very rare occasions. Herbicidal soaps are the least-toxic form of herbicide, and they are sometimes effective on some annual weeds.
More Resources
Start with the Soil by Grace Gershuny
Golden Gate Gardening by Pam Peirce
The Gardener’s Weed Book by Barbara Pleasant
The Gardener’s Guide to Common-Sense Pest Control by Olkowski,
et al.
