How to Kill Weeds Naturally, Without Harming Your Other Plants
No matter how much careful planning you do, it's inevitable that a few annoying weeds will start popping up in your garden. When you spot them, don't reach for the weed killer right away; there are natural ways to kill weeds that will solve the problem in an environmentally-friendly way. If you spot just a few weeds sprouting in your flower bed, you can try pulling them out and digging up as much of the roots as possible. But if you're seeing more and more weeds taking over your garden, a natural remedy to kill weeds can help you take back your yard.
Chemical-Free Ways to Kill Weeds
If you want to avoid using weed killers or harsh chemicals of any kind in your garden, try these natural ways to kill weeds first.
Anything that covers and smothers weeds is a type of mulch, including biodegradable products like cardboard and newspapers. Mulch also helps conserve moisture. An organic mulch works best in two ways: It offers weed control, and it breaks down to make your soil more fertile. Use a 2- to 4-inch layer of organic materials, like pine bark ($8, Ace Hardware) straw, grass clippings from a non-chemically treated lawn, or bark. Wood mulches, however, draw nitrogen from the soil in order to break down, so it pulls nitrogen (and nutrients) away from your plants. Avoid placing mulch right up next to the trunks of trees or stalks of plants, which can lead to disease or decay.
During the heat of summer, place thin clear plastic across any area where you want to kill weeds. Leave the plastic in place for four to six weeks. The sun heats the ground and kills weeds and weed seeds, but the intense heat also kills beneficial organisms.
You can also use a propane torch ($24, The Home Depot) to scorch weeds. Just use extreme care and wait until a non-windy day to burn off weeds. Flaming weeds will also kill nearby grass and other plants, so it's best for using in areas without plants that you want to keep, such as between the cracks of a concrete sidewalk.
Grab a dandelion weeder ($10, The Home Depot), which is a tool with a forked end, to dig deep into the soil to loosen and pry up a weed's roots. There are even long-handled versions that allow you to stand up while removing weeds. If roots remain in the soil, they may regrow. If you don't have the right tools, pulling the plant out as close to the roots as possible is the next best thing.
Boiling water kills plant tissues, but like flaming, the stream of water can be hard to control if you are trying to do spot weeding.
Natural Weed Killers
Any herbicide you choose, whether it's an organic (sometimes called "natural") compound or a synthetic one, has its benefits and drawbacks. These organic weed-killer products work, but they also have a few limitations.
Acetic acid is the active ingredient that makes vinegar a weed killer. White vinegar contains about 5% acetic acid. This vinegar burns the tops of weeds but is less likely to kill a weed with well-established roots. For a vinegar weed killer to be most effective, you'll have apply it frequently. It can also kill nearby plants if you're not careful.
Corn Gluten Meal
Dr. Nick Christens at Iowa State University discovered that corn gluten meal ($37, Ace Hardware), a byproduct of corn milling, works well to prevent seeds from growing. This pre-emergent organic herbicide is often sold as a lawn weed-control product. In order for it to be effective, you have to apply it at just the right time in spring before weeds begin to sprout. Usually, it also takes a few years of consistent applications to reach its full potential. Just avoid applying corn gluten meal in any beds where you plan to sow other seeds because it'll also prevent them from growing
What Not to Use: Salt
It's true that salt kills plants, including weeds, but it also poisons the ground for many years and moves with rain or water into groundwater sources. It's a bad idea to use it anywhere in the yard, so steer clear of homemade weed-killer recipes that call for salt or Epsom salt, vinegar, and dish soap. Both the salts and soap are toxic to the environment and should be avoided.