And yet the organic gardener is well served by cultivating a healthy tolerance for some weeds. Complete eradication is unnecessary unless something as insidiously invasive as Canada thistle (Cirsium arvense) or multiflora rose (Rosa multiflora) crops up in your backyard. By tolerating a few weeds, you will make your entire gardening experience more relaxed and enjoyable. And your garden will still be beautiful. There are as many shades of green in this world as there are of gray.
In The Eye Of The Beholder
The concept of "weeds" is a human invention, a way to describe those plants that grow where we don't want them. The mint grown by the last gardener who lived in my house is my idea of a weed. Yours may be volunteer tomato plants from last year's crop that show up in your flowerbed. One strategy for becoming more weed-tolerant is to rework your definition of a weed. A common gauge for weed tolerance is the relative difficulty of getting rid of the plant; perennials with spreading roots, such as quackgrass (Agropyron repens), or deep taproots, such as common pokeweed (Phytolacca americana), are the most persistent, so you will want to keep after them.
Many plants maligned as weeds, such as milkweeds (Asclepias spp.) and prostrate knotweed (Polygonum aviculare), are highly attractive to beneficial insects that will help pollinate your plants and eat aphids, thrips, and mites. Others are actually delicious edibles. These include dandelion (Taraxacum officinale), common purslane (Portulaca oleracea), miner's lettuce (Montia perfoliata), and common lamb's-quarters (Chenopodium album). (Just be sure you have positively identified an edible weed before adding it to your salad mix.) Some serious invaders such as pampas grass (Cortaderia selloana) and Himalayan blackberry (Rubus procerus) were prized as ornamentals before they bolted beyond the backyard.
Because their seeds are typically amazingly mobile, weeds can take over quickly. They're spread by birds, the wind, running water, and car tires. Trading plants with friends and neighbors often means trading weed seeds, too. In fact, anytime plants are brought into a new environment, they have the potential of bringing weeds with them.
An Ounce Of Prevention
Even if you do embrace a more casual attitude toward weeds, you'll want to control their growth by focusing on prevention as well as eradication. Weeds are opportunistic plants, popping up wherever conditions allow. With that in mind, think about all the things that you do to stimulate plant growth. Now, to suppress weeds, do the opposite.
Yank Them Young
Your first defense against weeds is to pull or hoe them before they get established. Learn to identify weeds as young seedlings and nab them as they emerge.
Stop The Seed
If you don't get them as babies, at least don't let them go to seed. As the old gardening saw goes, "One year's seeding makes seven years' weeding."
Organic mulches include compost, shredded leaves, wood chips, bark, dried grass clippings, and other biodegradable material. A 2- to 3-inch layer will keep sunlight from reaching the weed seeds, preventing their germination. Apply mulch immediately after weeding or digging your soil. Take care to keep mulch an inch or two away from plant stems to prevent rot caused by moisture retained in the mulch. Your mulch material will also conserve water, keep roots cool, and nourish the soil as it decomposes.
Grow plants close together, and they will consume the available space, nutrients, and sunlight, thereby bullying the weeds out of the way.
Remember not to yank perennial weeds. You'll break off the root, and another weed will appear. Use a long screwdriver or weed-pulling tool with a forked end. Hand-pulling becomes easier as your soil improves.
Pick Your Day
Weeding can be an absolute joy after a deep, soaking rain, but don't do it when the soil is soggy. You'll create clumps. And be careful where you walk and kneel: You don't want to compress your soil. Stay on paths and lean into your planting beds instead.
You may need to use a shovel to dig out persistent perennial weeds. Get as much of the root and runners as you can. It may take several diggings to eliminate something particularly tenacious, such as Canada thistle.
Use a diamond-shaped or hula hoe to scrape off the top layer of annual weeds. To avoid harming the roots of your cultivated plants, don't dig deeper than 1 inch. Deep hoeing also exposes buried weed seed to sunlight, allowing it to sprout.
Some gardeners use plastic sheeting, newspaper, and weed-barrier cloth as mulchlike covers. You lay the material over your planting areas and cut holes for your plants to grow through. This blocks out light and smothers young weeds. Other folks (like me) feel that nonorganic mulches are somewhat out of place in the garden. Trying to achieve a weed-free yard is a demanding, unrealistic goal. By simply accepting a few weeds as part of the mix, you will encourage diversity, welcome tasty additions to the salad bowl, and find yourself with more time for valuable gardening experiences, such as afternoon naps in the hammock, something any civilized person can relate to.
Lisa Van Cleef writes the Green Gardener column for the San Francisco Chronicle's online edition at www.sfgate.com.
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