Keyword: Organic gardening

A common question we get at the Elisabeth C. Miller Library is How do I kill weeds without hand digging but without using toxic chemicals? Further discussion with the gardener reveals he wants to buy a product that he can spray on the weeds, once. Organic gardeners have it easier now compared to a decade ago, with a number of less-toxic weed killers on the market, but the fact is not one of these products is a magic bullet.

• Corn Gluten Meal (Concern’s Weed Prevention Plus and Whitney Farm’s Weed Whompin Mulch) is a natural product that prevents seeds from rooting once sprouted. The downside is that it doesn’t work during rainy weather. Another consideration is that recent studies show it acts as fertilizer because it is rich in nitrogen, so in garden beds it may actually increase weeds. Its best use would be for weeds in lawns, according to an article in Organic Gardening, Aug/Oct 2008.
• Potassium salts of fatty acids (Safer Superfast Weed & Grass Killer) kills the tops of all plants, but not the roots. It works best on annual weeds like chick-weed and bitter cress, but would have to be repeated a few times to kill perennial weeds with root reserves, such as dandelion.
• Pelargonic acid herbicide (Scythe) is another type of fatty acid, similar to soap, that kills weeds by drying out the leaves. As mentioned above this product works best on annual or biennial weeds and must be reapplied a few times to kill perennials.
• Vinegar from the kitchen doesn’t kill weeds, only disfigures them. Commercial products (Burnout, Bradfield’s Horticultural 20% Vinegar) work if used in hot weather, but are quite caustic and great caution must be used not to inhale the fumes or spray the skin. Natural, yes, but toxic.

What does it take to get rid of weeds? A multi-pronged approach: physically remove weeds when they are young, reapply mulch every year, shade weeds out with desirable plants, and don’t let weeds go to seed.

The Northwest Center for Alternatives to Pesticides publishes excellent articles on non-toxic pest control. Two good articles on weed management are available free online:
Managing Weeds in Shrub and Flower Beds and Landscape Weed Control