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Control weeds in organic garden, landscape

By Mark Czarnota
University of Georgia

Many people don't like to use synthetic herbicides in the landscape. But weeds can be a big problem with any gardening practices. With organic gardening, prevention is one of the most essential ways to keep weeds out.

Many horticultural and agricultural practices are allowed with organic agriculture. But if any chemicals are used, they should come only from plant or animal sources.

Follow these tips

Here are a few tips to help keep weeds out of the landscape and garden and do so organically.

Prepare the site to be planted. Plowing, rotary tilling and other means of soil cultivation are still very good methods of weed control. Prepare the site to be planted with at least one good tilling.

If you're not in a hurry to establish your plantings, several cultivations three or four weeks apart will eliminate many difficult weeds.

These continual tillings disturb weed growth and help eliminate weeds. Weeds like nut sedges (Cyperus species) and Bermuda grass (Cynodon dactylon) primarily come from vegetative structures such as rhizomes and tubers, and plants coming from vegetative structures won't survive continual cultivation.

Get them early. It's much easier to hoe or pull out those weeds when they're small. The bigger weeds are allowed to grow, the more they will compete with desirable plants for light, water and nutrients.

Get to them before they flower

At the least, try to remove the weeds before they flower and produce seeds. Some fully grown weed plants, such as lamb's-quarters (Chenopodium album), pigweed (Amaranthus species) and spurge (Euphorbia species), can produce thousands of seeds.

Removing these weeds while they're small removes a lot of seeds you and your future generations will otherwise be fighting.

Mulch! Bare-ground planting is very hard to keep weed-free and is usually left for large-scale row-crop or vegetable production. Besides smothering weeds and preventing their germination, mulches help to maintain soil moisture and temperature and add organic matter to the soil.

If the landscape is to be permanently planted and no bulbs or annuals will be planted, consider using a landscape fabric under the mulch. The fabric will help smother those tough perennial weeds.

Wash your equipment when you complete a job. Soil stuck on equipment can easily transfer weed seeds from one site to another.

Don't bring in weeds. Weeds, such as nut sedge, often rear their ugly heads when they're brought in with nursery plants. To avoid bringing these weeds into the landscape, carefully select nursery stock.

Organic products available

Only a few organic herbicides are available. One, pelargonic acid, is popular with organic growers. It's sold under several trade names, such as Scythe and Quik II, and is basically a concentrated soap you mix with water and spray over the top of weeds.

Pelargonic acid causes plant cells to fall apart. It kills most weeds, as long as they don't have extensive underground rhizome or tuber systems.

Vinegar (acetic acid) is marketed in several products, such as Garden-Ville Natural Weed Control, and also works at burning down emerged weeds. Common table salt, one of the first herbicides, is still used to control weeds in driveway and sidewalk cracks.

Some plants are adept at making their own herbicides. One good example is black walnut (Juglans nigra), which produces juglone. Produced in many parts of black walnut trees, juglone kills or reduces the growth of plants growing under and around tree canopies.

In the future, we may be able to take the genes that produce juglone and transfer them into a plant like corn. Imagine that: a plant that can make its own herbicide.

(Mark Czarnota is an extension horticulturist with the University of Georgia College of Agricultural and Environmental Sciences.)

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