Organic Methods to Control Weeds

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Most gardeners don't actually enjoy pulling weeds by hand, but many don't want to use herbicides with potentially harmful chemicals either. Fortunately, there are various ways to take care of weeds organically. Unfortunately, some of the techniques -- including hand pulling -- are time- and labor-intensive.

Pre-emergent Methods

You can apply a mulching material or spread corn gluten meal over target areas to smother existing weeds and prevent weed seeds from sprouting.

Mulches

Layers of dried leaves smother unwanted weeds.
Layers of dried leaves smother unwanted weeds. (Image: AlexeyVS/iStock/Getty Images)

Organic mulch is particularity effective when it comes to controlling annual weeds because those unwanted plants have trouble penetrating thick layers. Not only does mulch prevent weeds from sprouting by blocking the sunlight they require for germination, but it also keeps plant roots warm in cold weather and cool on hot days. In addition, it adds organic matter to the soil as it decomposes. Just make sure any mulch you use is weed-free or you're just contributing to the problem.

You have your choice of organic mulches that offer good weed control. Adding a 6- to 8-inch layer of straw kills weeds, but you'll have to replenish the layers more often because the material breaks down quickly. A 2-inch layer of grass clippings not only smothers the weeds, but the grass also releases nitrogen as it breaks down. Make sure the clippings haven't been treated with herbicide before spreading them, however. The Virginia Cooperative Extension suggests using a 2- to 3-inch layer of compacted leaves or bark, while Texas Gardener recommends applying a 6-inch layer of hardwood mulch for optimal control.

Organic mulches break down, so replenish when necessary to keep layers at their original depths.

Tip

  • Some gardeners lay down layers of newspaper beneath organic mulch to kill weeds even faster.

Warning

  • Keep mulching material a few inches away from stems and trunks to avoid plant health issues.

Although inorganic, black plastic mulch controls stubborn perennial weeds better than organic materials. Black plastic boosts the soil temperature about 8 degrees, so the material can cause soil to get too hot in the summer. On the plus side, the plastic reduces the need for watering and it's a lot slower to break down, so you might need to replace it only once every other year or so. Bury the edges of the plastic about 3 inches deep so the material traps the heat necessary to kill the weeds.

Corn Gluten Meal

Corn gluten meal works as an organic pre-emergent herbicide because a protein it contains prevents the roots from growing on newly emerged plants. Although it doesn't directly kill the seeds, it makes treated seedlings vulnerable to desiccation when you allow the soil to dry.

Read and follow the directions on the product's label. Experts at the Iowa State University Extension recommends applying CGM at 20 pounds for every 1,000 square feet of lawn space, but application rates run from 20 to 60 pounds for every 1,000 square feet of garden space. Use a spreader to apply CGM evenly over large treatment areas, and then water the CGM into the soil and allow it to dry for about three days. Reapply corn gluten meal if your area receives heavy rainfall during the drying out period.

For smaller areas, such as flowerbeds, hand spread CGM granules and lightly rake them into the soil. Water lightly and then allow the area to dry for 48 to 36 hours.

Warning

    • Corn gluten meal doesn't discriminate -- it'll kill crop and flower seeds as well as weed seeds. Don't use CGM in your vegetable garden or flowerbeds until your plants become established.
    • Keep in mind that while CGM works well as a pre-emergent herbicide, it has no effect on weeds once they've germinated. In fact, using CGM on established weeds can backfire because the nitrogen promotes plant growth. 

Post-emergent Control Methods

Remove small patches of weeds by hand.
Remove small patches of weeds by hand. (Image: AnnekeDeBlok/iStock/Getty Images)

Manual Removal

Weeding by hand is a good choice in garden beds with valued plants. Hand-pull weeds out of wet soils only. If the soil is dry, the weeds can break off just below the ground and resprout. Wear gardening gloves and kneel on a pad for comfort. Place a tarp within arm's reach so you can pile pulled weeds on it.

Grubbing weeds is less hard on your body than hand pulling, and it tends to be more effective when soils are dry. Mother Earth News suggests grubbing out weeds using a sharpened hoe at 10- to 15-day intervals throughout the summer to stop pesky weeds from competing with your food crops for growing space, nutrients and moisture.

Chopping off their heads stops annual weeds from seeding and forces perennial weeds to use up their reserves so they can't spread. Mother Earth News recommends waiting until after rainfall or irrigating the soil beforehand and then cutting 1/2 to 1 inch off the top using pruning loppers or a weed eater with a blade attachment.

When finished manually removing weeds, carefully place seeded weeds in a plastic garbage bag that you promptly toss in a covered outdoor trash can. You can toss young weeds that haven't seeded yet on your compost pile without worrying about them spreading.

Boiling Water

To control small or localized weed patches, dump boiling water over them. Pour carefully, use hot pads and wear close-toed shoes and long pants so you don't accidentally scald yourself. Boiling water can kill off beneficial soil organisms along with the weeds, so don't use it in areas where you plan to grow plants in the near future.

Keep in mind that the water temperature must be over 200 degrees Fahrenheit for it to kill weeds. Water temperatures drop quickly once you take the pot off the stove, so you've got to move quickly for this organic method to work.

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