Here's how to match your spring planting with last year's cover crop

Julia Bayly, Bangor Daily News, Maine
·3 min read

Apr. 14—That cover crop you planted last fall did its job. But now what? That's an important question for gardeners. Fortunately, you have options.

There are two kinds of cover crops. Living cover crops like winter rye can survive a Maine winter and reseed in the spring. Dead cover crops like oats or buckwheat can't make it through the winter. Both are useful fall plantings that can add nutrients to the soil. But what happens come spring?

"There's a big difference if you have a living cover crop like winter rye or a dead one like oats," Caleb Goossen, organic crop and conservation specialist with the Maine Organic Farmers and Gardeners Association, said.

When it comes to living cover crops, if you don't plan on planting that land, simply leave them alone to reseed and grow.

But if you intend to plant for fall harvest, you need to kill the cover off first.

"With a living cover crop my recommendation is to try to terminate it as soon as possible [if you want to plant]," Goosslen said. "That means killing it as early as you can in the spring or let it grow until it reaches the point just as the flowers are shedding pollen but not yet being pollinated."

So how do you do that? One option is to cover it with heavy agricultural tarps or large sheets of thick cardboard. These are not the blue tarps commonly found at hardware stores, but rather a tarp intended to prevent sunlight from hitting the plants.

If you wait until the flowering stage — known as anthesis — to kill the cover, Goossen said, you can crush the cover crops and break them up with a device known as a roller-crimper. A roller crimper is a weighted drum with attached blades that goes on the front of a tractor. It acts like a mower that chops the plants down and cuts them into small pieces.

"When a plant is in anthesis it is done with reproduction but has not started to seed out or spread pollen," Goossen said. "If you knock it down at that point it should not come back."

However, if your cover crop was a winter kill crop that's now dead, you may be able to plant directly into the dead remnants of that cover crop, depending on what you are planting.

"Some folks go for a winter kill cover with that intention of planting directly into it in the spring," Goossen said.

That winter cover crop can also act as a natural mulch and keep weeds down. But before you decide to plant directly into it, you need to balance the advantage of natural weed prevention with the fact the plant residue is going to block warmth from the sun reaching the soil.

"Keeping your soil cooler in the middle of summer is beneficial," Goossen said. "But it's a detriment in the spring when you want the warmth to break down nutrients and trigger your seeds to grow."

Dead cover crops can also make it difficult to mix in soil amendments like fertilizer or compost, so if you need to use those consider whether it's worth planting directly into the residue.

If you need to plant on a larger scale with a mechanical seeder, for instance, you won't be able to plant directly into the winter kill covers. Tines and other moving parts of the mechanisms are going to get tangled in the dead plants and clog up the seeder.

"On a larger planting scale, mechanical transplanters or tractor driven seeders are not typically designed to work in cover crop residue," Goossen said.

In that casem, you'll need to prepare the land first. Tilling will break up the dead plants and incorporate them into the soil. This way the residue will be broken up enough to not interfere with the planting machinery.