Think you’ll solve your weed problem by laying down some weed-barrier fabric, bark mulch and a few shrubs planted through a slit? This “permanent” solution may in fact cause more weed problems than it solves. Linda Chalker-Scott, Extension Urban Horticulturist, Puyallup Research and Extension Center, Washington State University did research to debunk this myth. Read about why
landscape fabric fails.
Keyword: Weed control
Garden Tip #139
Eradicating blackberry vines may seem hopeless, especially if you don’t want
to use chemicals, but don’t give up just yet. The Northwest Center for
Alternatives to Pesticides advises gardeners to cut off the top growth, dig
out the main root-ball, and then follow-up by mowing all new growth.
Planting desirable plants to shade out the sun loving blackberries is also
critical. Read the NCAP’s blackberry management plan (pdf).
Garden Tip #14
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
Garden Tip #111
The best time to pull up weeds with long tap-roots, like dandelion and yellow dock, is just after a good soaking rain. Even without a special tool, the tap-root can be wiggled a bit and then tugged right out of the ground. If even a bit of root is left behind it will regrow, but the plant will be weaker and will eventually die if the tops are cut off repeatedly. A good article on controlling dandelions organically is available from Northwest Center for Alternatives to Pesticides.
Garden Tip #112
As the garden grows, so do the weeds. Act early before the problem gets totally out of hand. At the very least don’t let the weeds go to seed. The book Maria Rodale’s Organic Gardening (Rodale, 1998) has a chapter on fighting weeds that includes suggestions for getting motivated. The author suggests focusing weeding efforts on just one defined patch per session for a set amount of time. She also reports the best motivator of all is a deadline: invite your friends and family over for a Sunday afternoon barbeque and be amazed at how much weeding gets done in the morning.
Garden Tip #197
Weed fact sheets are available from UC Davis, in cooperation with the Nature Conservancy. This is an excellent resource for learning how to control some of the most tenacious invasive plants in the US. Many weed profiles have color pictures, “success stories,” and references to research.