Vinegar Update

One way to cure a garden of reckless weeds is spray them with white or apple cider vinegar. "I know that using this stuff as an herbicide isn’t exactly new," says master gardener Paul James, "but I've been using it for years. Vinegar controls many weeds, especially tender young annual weeds."

Figure A

To apply, pour the vinegar straight into a spray bottle, and thoroughly mist the weed to be removed. In about one week, especially during 90-degree weather, the weed dries up. (In cooler climates such as the Pacific Northwest, however, vinegar doesn't work nearly as well.) Vinegar strips the waxy protective coating from the plant surfaces, causing the leaves to dry out and often desiccating the plant all the way down to the roots. Paul recommends spraying the weeds two to three times a day at 5- to 10-day intervals.

This all-natural weed treatment is not without some problems, though. One thing to remember about vinegar is that it's non-selective, meaning that it destroys anything green, whether weeds or a prized plant. Take extra care when using it, and avoid vinegar treatments altogether on windy days.

Another problem is that regular store-bought vinegar, which contains only 5 percent vinegar or acetic acid, isn't strong enough to deal with persistent problem weeds. However, you can now buy vinegar that is especially developed for use as an herbicide, and it contains 20 percent acetic acid, four times stronger than the kitchen variety. Garden vinegar does a much better job of eliminating tough, nasty weeds.

Also, too much vinegar can have an adverse affect on the soil's pH level. "After all, vinegar is pretty acidic," explains Paul, "so I suggest you use it only to spot treat weedy areas in flower beds rather than in or on the lawn, and don't over-do it when spraying." Treating a large area of lawn soaks the soil with too much vinegar, resulting in an overall decrease of the pH level. "Actually, some people do douse the soil with this stuff to lower the pH to the point where few if any plants will grow," says Paul, "but I don’t recommend it for that use because it renders the soil inhospitable to plants for at least six months."

Figure C

On the other hand, using vinegar to control weeds around acid-loving plants like azaleas, is a great way to treat the weeds and lower the soil pH, especially if the soil is too alkaline.

Caution: Never use the garden-variety (20 percent acetic acid) vinegar for cooking.

Citrus herbicides

Herbicides made from various citrus oils and from oils of cloves and cinnamon work every bit as well as concentrated vinegar, and they smell a whole lot better, too. "Actually, I know of at least one product that combines citrus oils and concentrated vinegar for that one-two punch," Paul says. "But again, although that may sound like the basis for a tasty vinaigrette, these products should never be used for cooking or eating. "

Figure D

Citrus-based herbicides are similar to vinegar herbicides in that they are also non-selective when it comes to plants. So Paul recommends spraying only the plants you want to eliminate. If you need to spray near other plants in the garden, protect them with a piece of plastic or cardboard as you spray the weeds.

Although vinegar and citrus herbicides contain all-natural ingredients, that doesn't mean that they don't pose a threat to humans and other critters. "Try to avoid using them when the bees are buzzing and other beneficial bugs are active, and avoid using them near ponds that contain fish, or near edible food crops," says Paul. Also, remember to wash your hands thoroughly after using any garden chemical whether natural or synthetic, and consider wearing gloves while spraying.