Every year as fall transitions into winter, and again as winter changes to spring, something amazing — and a little terrifying (for a farmer) happens in our fields. The weeds in our fields change. The warmth- and sunshine-loving weeds that torture us for six months of the year stop sprouting. And any that remain begin to produce seeds, even if they are only a few inches tall.
It’s not that hard to understand how a plant might sense that the days are getting shorter and the temperatures are dropping. But it’s a little more difficult to wrap your head around the idea that a seed — as tiny as a speck of dust — might sense the change in season.
Backing up a step: every cup of soil contains hundreds, thousands or even more seeds in it. These build up over the years, and sprout in response to specific events. It might be a certain amount of moisture from rain or irrigation, a disturbance of the soil that exposes them to light, a certain temperature, a fire or something else.
For a few weeks every fall, almost no seeds germinate in our fields. We always know what is coming — a “flush” of winter weeds, particularly grasses that grow faster than our winter crops and are difficult to kill in cool, wet weather. But they wait — for rain.
No matter that we are irrigating our fields regularly until the first storms arrive. Somehow, the winter weeds “know” the difference between rainwater and well water. During the drought, when it hardly rained at all in the winter, they did not sprout at all. And if it rains in October, the winter weeds sprout, giving us a chance to remove and control them. This year, the rain waited until Thanksgiving, and so did the weeds. Within three days, there was a carpet of grass all over the farm fields.
It’s not that surprising that weedy plants might prefer fresh rainwater to water coming from two hundred feet underground. Our crops certainly prefer it, and almost always go through a little growth spell when they first get it. But it’s harder for me to understand how seeds, buried in the ground, might be able to detect the different chemical makeup of the water — high oxygen levels, lower salts, etc.
After a late start to the rainy season, we’ve caught up quite nicely and precipitation is currently just above average, year-to-date. Unfortunately, so are the weeds. So now it would be nice to have a little dry spell to get out there and take some of them out.