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Weeds in Your Garden

We all agree that a weed is just as bad as insects and diseases in your garden, right? Well, maybe not so right. Just as all insects aren't pests, not all weeds are bad. In fact, some of them have particular virtues that make them not only tolerable, but sometimes welcome in the companion garden. Dandelions root deeply, breaking up compacted soil and bringing up nutrients. Goldenrods and oxeye daisy are great hosts for beneficial insects. Wild mustard and pigweed can trap insect pests, luring them away from your crops. Low-growing weeds, such as purslane and knotweed, can keep the soil cool and shaded. And corn cockle can release compounds that help other plants grow. So, if carefully managed, some weeds can be quite useful as companion plants.

Management is the Key

Before you allow any weeds to stay in your garden, learn about them. Find out if they have rampantly spreading roots that are difficult to curb or if you need to deadhead so you don't have hundred of weeds next season crowding out the very plants you are trying to help. Also, some weeds can harbor the same diseases as your crops, making them poor companions. Some weeds attract the same pests, making the weeds excellent trap crops. Here are some of the more common garden weeds and how they may benefit or hurt your garden.

Corn cockle (Agrostemma githago): This softly hairy, purple-flowered plant grows well with winter rye and wheat. Corn cockle produces agrostemmin which is a compound that improves the growth of wheat. The seeds are poisonous, though, so make sure you don't grind them up with your wheat.

Jimsonweed (Datura stramonium): This poisonous annual has toothed leaves, stems as high as 5 feet and trumpet-shaped flowers. It shares the same diseases and pests of peppers, potatoes, and other members of the tomato family. It could be used as a good trap crop for Colorado potato beetles.

Lamb's-quarters (Chenopodium album): The silvery, triangular leaves and shoots of this annual are very attractive to aphids, making it a good candidate for a trap crop.

Wild Mustards (Brassica spp.): Annual mustards have toothed or lobed leaves and four-petaled yellow flowers. They can serve as a trap crop for cabbage pests.

Black Nightshade (solanum nigrum): This poisonous annual has slightly toothed leaves and tomato-like flowers. It may trap Colroado potato beetles and kill the larvae, but it also will cary pests and diseases that attack tomatoes, peppers, and eggplants.

Pigweed, redroot (Amaranthus retroflexus): This prolifically seeding annual has red stems and a deep taproot that helps condition soils.

Queen-Anne's-lace (Daucus carota var. carota): This biennial has feathery leaves and a lacy umbrella-shaped head of white flowers that attract beneficial insects. It also has a deep taproot that can break up compacted soil. If you leave plants in the garden, remove spent flowers to prevent reseeding.


Not all weeds have redeeming properties. Many of the plants that spring up in your garden are agressive and undesirable. Perennials such as bindweed, sorrel, and ground ivy spread by creeping roots or stems and take a lot of hand weeding to eliminate. Even the "beneficial" weeds like lamb's-quarters and wild mustards can take over if you let them set seeds. Large numbers of weeds can compete with your crops for light, water, and nutrients. Certain weeds - including crabgrass, peppergrass, curly dock, and common milkweed - are aven allelopathic, releasing inhibitory chemicals into the soil or air, thus preventing other plants from growing nearby.

Weeds can also carry pests and diseases that attack garden plants. Catnip, milkweed, and pokeweed can carry cucumber mosaic virus, a problem on most crops of the squash family. Wild cherries can be infested with black knot fungi that will attack cultivated cherry trees; wild apples and pears can be a reservoir for the infectious bacterial disease fire blight. Wild asters can carry a wilt disease. When diseases are a problem, don't take a chance - eliminate weedy disease sources, despite any virtues they may have.

Check with your local Cooperative Extension office to find out whether any of the weeds you are "harboring" might be considered noxious weeds. Keeping them could put a hole in your pocketbook from county fines.

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