When I was a kid, I thought dandelions were cool, from their delightful yellow flowers that broke up the monotony of green lawns to their puffballs of parachute-wearing seeds which were so much fun to blow into the neighbor’s grass. Now that I’m grown up, however…well, actually, I still think dandelions are cool, but those of you who prefer your lawns smooth, lush and green probably feel differently. That’s because dandelions, for all their charm, are considered “weeds.”
A weed is any plant that causes a nuisance or hazard to us, our animals or our crops. Even an extremely useful plant is a weed if it’s growing where it’s not wanted, as the dandelion proves. Dandelions are attractive and completely edible–and a good source of important nutrients–but lawn-growers still try to destroy them on sight. They’d do the same to a stalk of wheat. If a plant grows where it’s not wanted, it’s a weed…which is why we have so much trouble with weeds. Plants, oddly enough, couldn’t care less what we want.
Weeds often seem to grow better than the plants we’re trying to grow. That’s because we’re often trying to grow plants in places for which they aren’t ideally suited. When a weed sprouts in a particular spot, though–say, right in the middle of your carrots–you can be sure that’s a good place for it to grow. Often it springs up first and grows fastest, and, as it grows, steals more and more nutrients, water, and even sunlight from the plants around it.
For most of past few millennia, controlling weeds has meant a lot of hard work: you either plowed, mowed or hoed them down. But many perennial weeds have underground root systems from which they can regrow; and cultivating a field over and over again to keep the weeds down, we’ve learned in Saskatchewan, carries with it the danger of drying out the field and seeing it blow into Manitoba. Mowing is an even more short-term solution.
The best you can hope for is to give your crop–or lawn–the opportunity to grow first and fastest, and choke out some of the weeds, instead of the other way around. That means one of the best ways to control weeds is to make conditions–soil pH, moisture, depth of planting, spacing–as close to ideal as possible for the plants you want to grow.
Crop rotation can help, too (although it’s obviously not practical for lawns). If you grow the same plants in the same spot year after year, you also favor the same weeds year after year, which means you’ll see more and more of them.
Humans finally got some new weapons in the war against weeds in the 1940s, when the first synthetic herbicides came onto the market.
Most herbicides are selective, killing certain groups of plants and not others. 2,4-D, for example, kills many broad-leaved plants but doesn’t damage grasses, whereas dalapon controls grasses but doesn’t affect broad-leaved plants. However, there are also broad-spectrum herbicides that kill just about everything, and some “soil sterilants” that make it hard for anything to grow for some time; they’re mostly used along railroad tracks and roadways and on parking lots and industrial sites.
Different herbicides work in different ways. Some interfere with a plant’s normal growth and development by disrupting protein or amino acid synthesis. Some prohibit photosynthesis, either by messing up the process within the cell or preventing the manufacture of the necessary pigments. And some react with sunlight to produce compounds that actually rupture the plant’s cell membranes.
Some herbicides are applied to the soil and others to the weeds themselves. Those applied to the soil enter the plant through the root system; those applied to the plants may either kill only the part of the plant they touch (contact herbicides) or be taken into the plant and transported to all parts of it, killing the whole plant. Which type of herbicide is used depends on soil conditions, rainfall, the type of weed being attacked and the type of plant being protected.
Herbicides have improved the control of weeds, but haven’t eliminated them. Nature, it seems, just doesn’t understand humans’ desire to have a lawn like a billiard table, or why we have such a strong aversion to wild oats mixed in with our regular oats. And so the battle against weeds will continue all summer long, as it has for thousands of years.
Personally, I’m staying out of it.
Dandelion wine, anyone?