Weed: a plant that is growing in a place where it is not wanted. American Heritage Dictionary
One of the courses I used to teach was general biology, which was required of students who were not majoring in science. Some of the faculty didn’t like teaching it because it was not in their field of specialty, but I always enjoyed it; it was a challenge to capture the interest of those students. The
course included a unit on ecology, and one of the lectures I designed for it was entitled "Why We Have Weeds." Although it has been several years since I last taught it, the topic still comes back to mind every year about this time.
Our garden has had a tough time getting started this year. It was too wet to plow at the usual time, so, to my wife’s increasing agitation, I waited. The pressure increased, and late in April we finally had four consecutive days without rain, so I plowed. But it was still too wet, and walking on the soil
just to make the rows and plant the seeds compacted it pretty badly. Then, the day after we planted it rained heavily, and the seeds got washed everywhere. Those that didn’t rot came up in unexpected places, downhill from the straight, orderly rows where they were supposed to be. I think my wife rather liked that; too much
organization makes her nervous, and that week when the seeds first came up was the most relaxed I’ve seen her this year.
As soon as it dried a bit, I redid the rows and planted new seeds. As they came up, I surreptitiously began pulling out the plants that were in the wrong places, a few at a time; I didn’t want them between the rows, so by definition they were weeds. Order gradually returned, but with it came the real
weeds. Like their domesticated cousins, they got off to a slow start because of the wetness, but they soon made up for it and grew like… well, like weeds. The battle was on, and will rage the rest of the summer; the weeds will not call a truce if we happen to go away for a week on vacation. It is a battle as old as life itself;
ecologists call it "Succession," and it went on before there were gardens, or even people.
Succession is the process by which plants and animals organize themselves into a "community," i.e., an interrelated group of species best adapted to the climate of a particular place. In this part of the world, if you would remove all living things from an area and then leave it alone, succession would go
through a series of stages, each consisting of a group of plants that is more complex than the group it replaced. Eventually a forest community would develop, much like what was here before the country was colonized in the 17th century. It would take time… one or two centuries… but in ecological terms, it would be inevitable and
predictable. It would begin with weeds.
Weeds are nature’s colonizers. Their role in nature is to move into an area that has been denuded of vegetation by some sort of ecological disaster, such as a forest fire, volcanic eruption, flood… or plowing a garden. To survive, they have to be tough. They must be able to grow on poor soil; disasters
like floods or fires often destroy the topsoil and leave nothing but bedrock. Weeds adapted for the earliest stage of succession have no trouble growing in the cracks in suburban sidewalks or the asphalt of abandoned tennis courts; they have roots that go deep for moisture, and leaves that can withstand the summer’s heat without
wilting. At the end of the growing season the leaves and stems die back to the surface, where they trap particles of dirt that are washed or blown into the area; this material builds up over the course of time, and eventually gives rise to topsoil.
The second stage of succession is done by weeds that grow on topsoil; these include the common garden species. Their life is competitive, so many of them are equipped with protective devices such as thorns, poisons or bad-tasting chemicals. They are designed to grow fast and produce large numbers of
seeds. These seeds have a variety of dispersal mechanisms; they may float in the air, stick to the fur of passing animals, or survive the trip through a bird’s digestive system and thus be deposited far from where they originated (this is why plants like poison ivy are found growing in fencerows so often). Weed seeds are also
designed so they will not germinate all at once; thus, even if you keep your garden free from weeds all summer, there will still be seeds there from years ago, and some of them will come up next year.
Over the years I have developed a kind of respect for weeds. After all, they are specialists, doing their job as best they can under difficult circumstances. But I’m not sentimental about them; I still root them out as fast as I can keep up with them. Nevertheless, it is interesting to watch the sequence
of different species that appear over the course of the summer; you can easily find over 30 species in a garden the size of mine. Occasionally there are surprises; this year, there are a remarkable number of silver maple seedlings. Some weeds have attractive flowers, so I may leave a few for the grandchildren to see. In
particular, I always try to leave a few milkweeds in the uppermost row, so the kids can see monarch butterfly larvae feeding on them.
Until this year, my wife had taken a simpler approach (if you’ve seen one weed, you’ve seen them all), and ripped them out indiscriminately, including my milkweed collection. This spring, however, she happened by chance to hear a talk by someone from a master gardener’s organization, and came home
delighted with the newfound knowledge that milkweeds are the food of monarch butterflies. My first impulse was to complain that I had been telling her that for years; but I finally decided I’d better accept whatever method it took to get the idea across. The result is that among the sweet corn in the upper row we have the best
crop of milkweeds I can recall, and as this goes to press we’re waiting for the monarchs to show up. There’s nothing like a weedy garden to bring a family together.
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