Ask a Master Gardener: Environmentally-friendly weed control methods

Published 3:30 am Wednesday, August 6, 2025

We don’t want to use commercial herbicides in our garden. One neighbor uses vinegar and corn meal to get rid of weeds. Another burns his weeds using a propane torch. Do any of these methods work?

Because most gardeners are looking for easier ways to deal with weeds and options that are less harmful to the environment, a variety of “innovative” weed control methods have emerged.

Some of these methods have merit but work only in limited circumstances. And some have serious drawbacks. The three approaches mentioned have gotten a lot of press.

Acetic Acid

High concentration (10-30%) acetic acid — as opposed to household vinegar, which is about 5% acetic acid — has been shown to have significant herbicidal action. When sprayed directly on most plants, it causes the cells to rupture and die.

High concentration acetic acid, however, affects only the part of the plant it touches (i.e., the above-ground portion). Well-established weeds and those with strong root systems usually recover.

It also is non-selective and will damage desirable garden and landscape plants if the spray drifts.

Perhaps the biggest drawback to using high concentration acetic acid is that it is corrosive. It can damage concrete and metal and is a safety hazard for humans and animals, especially during its application.

Corn gluten meal

In the 1990s, researchers from Iowa State University stumbled upon the herbicidal action of corn gluten meal. When applied properly to the soil, corn gluten meal causes the soil to dry out, damaging the tender young roots of weeds as they emerge from the seed.

Corn gluten meal is not the corn meal you find in grocery stores. The latter is largely composed of carbohydrates. Corn gluten meal is a byproduct of the corn milling process and is 60% protein and 10% nitrogen by weight.

Conditions must be right for corn gluten meal to work. It needs to be watered in after application but then it must dry out. If it rains or you irrigate nearby plants, the soil will get wet, and the weeds will recover.

Corn gluten meal has little effect on established weeds. It also is non-selective and will harm germinating seeds of any plant.

Finally, corn gluten meal is expensive. A 50-pound bag costs about $50. Because most sources recommend an application rate of 20 pounds per 1,000 square feet, treatment of an entire lawn or garden could cost several hundred dollars.

Flame weeding

Flame weeding involves subjecting weeds to high intensity heat, causing exposed cells to rupture and die. The heat source is usually provided by a portable propane tank with a hose and nozzle to direct the flame.

You do not have to burn the weed to a crisp to damage the cells. Just a brief exposure to intense heat will work.

Like acetic acid, flame weeding damages only the above-ground portion of the weed; the roots often remain unharmed, allowing the weed to recover. It also is non-selective and will harm any plant that gets in the way.

The most serious drawback of flame weeding is the risk of fire. With recent dry conditions, you could do serious damage to your home, property, and maybe more.

Although the above approaches have some merit, a combination of the more tried and true methods (see below) might be easier and more successful for the control of weeds in your garden.

Note: Before attempting control of a weed, you must identify it. Control measures that work on some weeds will not be effective on others.

Physical removal of weeds through hand pulling, hoeing, and mowing: Because these methods tend to remove only the above-ground portion of the weed, weeds with a strong root system will recover. Repeated removal of the leaves and stems, however, will eventually starve the roots and kill the weed for good.

If a weed spreads through seeds, removal of the weed, or at least its flowers, before seed development is critical.

Gardening methods that discourage the establishment of weeds: If you carefully apply water and fertilizer to only the desirable plants in your garden and landscape, weeds are less likely to germinate and grow in the space between the desirable plants.

Several inches of mulch applied to open areas in your garden will shade newly emerging weeds and prevent them from becoming established. Those that germinate and grow are often easier to hand pull.

Cover crops can act as a “living mulch,” crowding out and shading emerging weeds. However, do not allow the cover crop to go to seed because it will become a weed in subsequent seasons.

Commercially produced herbicides: If used correctly, commercial herbicides are safe and, sometimes, the most cost-effective way to control weeds. Always read the label and apply the herbicide according to the label directions.

Although some herbicides are a broad spectrum and work on all types of weeds, some only work on certain plant types (e.g., grasses vs. broadleaf plants or newly emerging plants vs. established, actively growing plants). Make sure the herbicide you select is effective against the weed you are trying to control and its phase of growth at the time of application.

Successful weed control requires forethought, persistence, and a combination of approaches. For more information on the control of common garden weeds, see WSU’s Hortsense at https://hortsense.cahnrs.wsu.edu/weeds/

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Jeanette Stehr-Green is a WSU-certified Clallam County Master Gardener.