Controlling Weeds in Vegetable Gardens

A weed is any plant growing where you do not want it. Volunteer tomatoes growing in the mixed greens bed are weeds. Weeds are not always ugly, and many, such as purslane, dandelion greens, and lamb’s-quarters, are edible. But weeds rob vegetables of space, water, and nutrients.

Weeds come to your garden from four places: most are probably the offspring of weeds that went to seed in your garden, some blow in from the neighborhood, some have been brought in with mulch or manure, and some have been dormant in the soil until you brought them to the surface with cultivation.

The first rule of weeding is to keep weeds from setting seed. If you never let a weed go to seed in your garden, you will have greatly reduced your weed problem.

Another weed preventative is keeping the perimeter of the garden and the rest of the yard weed-free or mowed, and cutting down patches of wild grasses and flowers before they go to seed.

The manure, hay, and other organic materials you mix into the soil may bring their share of weed seeds. Compost and composted manure have been sterilized by the heat of decomposition and are usually weed-free, but fresh manure, hay, straw, and many other mulches and soil amendments are often laced with weed seeds. Germinate a batch of potential mulch by keeping it damp for a week or two to see what dark secrets it carries.

Turning new sod and working the land can bring up hordes of seeds, some that were dormant for years. When starting a new garden on soil that has been weedy for a long time, it’s often wise to use no-till methods to avoid stirring up trouble. See Controlling Weeds in New Gardens for instructions.

Hoeing and Pulling

The most critical period for weed control is the first few weeks after the ground begins to warm. This is generally right after you have planted the first vegetable seeds. Hoe the weeds weekly during this period of rapid growth. Hoeing is a breeze when the weeds are less than an inch high. Cut them off at the soil surface with a sharp hoe. Small weeds are easy to pull by hand if the garden is not too large.

Firmly rooted weeds are easier to pull after a rain or a thorough watering. A few weed seedlings are simple to pull by hand. However, some weeds will just re-sprout from roots or other underground parts if pulled out. Either dig them out to get all the roots or use an herbicide to kill them first, then cut them off at the soil line.

Tilling Weeds

Wide paths among the planting rows can be tilled instead of mulched to keep down the weeds. Manufacturers offer many types of small garden tillers. Do not rototill if quackgrass is present—you will only make the problem worse.

Herbicides

Herbicides are difficult to use in vegetable gardens, especially intensively-planted ones, because the plants are so close together. Use them to kill weeds before planting, and in paths or around the perimeter of the garden. When spraying, use low pressure and keep the sprayer nozzle close to the weeds to prevent getting any spray on the vegetables.

To kill difficult weeds in the vegetable garden, place a cardboard box without a bottom or top over the weed and spray inside it. This method will take care of dandelions that you have overlooked until they grew a tap root, or a patch of quackgrass trying to get established.

Preventing Weeds

Vegetables suppress the growth of weeds as soon as they are large enough to shade the ground. This effect is stronger if they are intensively planted. Weeds that manage to germinate in their shade are weak and easy to remove.

A mulch suppresses weed growth even better than a plant cover. Two to four inches of compost, composted sawdust, or other organic mulch prevent most weeds from germinating.

To completely stop all weed growth, mulch with black plastic, sheets of geotextile material, or five or six layers of newspaper. Newspaper rots into the ground in about three months. If you choose a geotextile product, use one that has a close weave. See Mulching Vegetable Gardens for more information.

Prevent weeds in paths by using a permanent path system. This allows you to pave the path, cover it with gravel or decomposed granite, or plant a lawn on it (make the path a width that’s easy to mow). All these methods avoid weedy paths as well as avoiding mud.

In row-crop gardens, where the whole garden is tilled every year, spread a deep mulch on the paths. This will prevent weeds and add to the organic matter in the soil when you till it in.