Barbara Pleasant - Controlling Garden Weeds

Barbara Pleasant

Weeds are the plants gardeners love to hate. Through the ages, people have attempted to define weeds, always with inadequate results. Are they plants whose virtues have yet to be discovered (Walt Whitman), guardians of the soil(Joseph Cocannouer), or something equally nice, or are they sly thieves that steal the soils resources and gardeners precious time? Perhaps they can only really be defined from a practical point of view: Weeds are any plants that insist on growing where you dont want them to grow.

It so happens that unwanted trespassers in your garden tend to be the same plants time after time. These true garden weeds are special, for they thrive on the constantly changing soil conditions that take place in gardens as we plant and replant our beds, borders, and rows. Many wild plants that are technically classified as weeds cannot tolerate the continual shifting about that we gardeners do, so its more fitting to regard them as wildflowers than as garden weeds. Examples include wild asters, daisies, ironweeds, goldenrods, and sunflowers. Rarely will you catch these roadside weeds trying to crowd out your tomatoes or attempting to steal nutrients from the soil you prepared for your lilies. These dastardly deeds are done by what I call garden weeds plants like crabgrass, redroot pigweed, lambsquarters, and others.

We tend to think of weeds as superplants because they do such a great job of invading our gardens, but in reality weeds can only thrive where we make a place for them. Garden weeds are experts at colonizing disturbed soil, which is exactly what a garden is to a weed a space where the earth has been opened up. For this much weeds must be respected. Weeds, in turn, have no respect for a gardeners goal of enriching land with beautiful, fragrant, delicious, and otherwise useful plants. Yet the missions of gardeners and the objectives of weeds are often the same: to bring stability to disturbed sites so that those places can regain their lost function in natures wild scheme. Weeds just go about things differently than we do.

Ecologically speaking, most garden weeds are weaklings in the long run. They do a terrible job of adapting to natural ecosystems (like a mature forest or grassy prairie). If you were to abandon your garden tomorrow and let nature have its way with the place, most plants that fit into the category of garden weeds would be gone within a few years. Garden weeds depend on humans to provide them with an open place to grow, and they further benefit from our efforts to keep garden soil fertile and moist. Where humans cultivate, garden weeds grow.

When planting seeds, we gardeners operate within countable numbers say, 25 seeds for a planting of squash, or a few hundred for a nice row of zinnias or beans. But most garden weeds produce so many seeds that its a small exaggeration to call their version of seed production a seed rain. In a good year, a healthy crabgrass plant can drop 100,000 seeds, and lambsquarters can beat that number five times over. Along with amazing numbers, weed seeds (and the roots of tenacious perennial weeds) have an almost supernatural gift of longevity. For example, if you were to bury an assortment of weed seeds a foot deep and leave them there for five years, when you finally brought them to the surface you could expect about 25 percent of them to sprout. Try the same experiment with seeds of cultivated onion or lettuce and germination will be zero.

All gardeners can assume that every square inch of their garden soil contains weeds. Some of them may have been there for years, while others dropped or blew in only yesterday. The seeds that exist naturally in any soil are called the soils seed bank. And just as with the dollars in your checking account, repeated withdrawals will make the balance go down. If no deposits are made (by allowing weeds to drop seeds or importing weed-seed-bearing manure or topsoil, for example), you can make your balance go lower and lower maybe by as much as 25 percent a year in the first three years. But you will never completely bankrupt your soils weed seed bank, for some seeds will always blow in or perhaps hitch a ride on the feet of a passing bird.

To drive the balance in your soils weed seed bank close to bankruptcy, the most important thing to do is to prevent weeds from shedding their seeds. Use mulches, cover crops, smother crops, cutting and mowing, hoeing, and hand weeding to keep weeds from developingand shedding seeds into your garden soil. Where weeds are allowed to grow and reproduce freely, about 95 percent of the weed seeds in the bank come from weeds that shed seeds in previous seasons.