Cover me

Steve Black is the owner of Raemelton Farms, a Maryland-based wholesale grower of 2- to 4-inch B&B shade, flowering, and evergreen trees and large shrubs. For the past few years, Black has been using in-row cover crops to aid in tree production. Loose, tilled-up dirt and rows of trees is still a common sight at farms across the U.S.

That leads to soil and water conservation issues and pest and disease management problems because of the hot, dry, dusty environment – particularly spider mites, which love dry, dusty soil.

Many East Coast nurseries have adopted grass aisles. They keep a bare strip where the trees are planted, but maintain a grass aisle in the area between rows. Black says this helps a lot, and calls it “the 80 percent solution.” But the next step is that strip under the trees. After a few years of experimenting, Black’s work on in-row cover has led to increases in production speed.

Keeping that row clear can be done through tillage, but that risks damaging your trees’ root systems and trunks. Planting cover crops is a better solution, Black says. They suppress winter annual weeds, provide excellent root action to loosen the soil, and provide nutrients as the young trees begin to grow.

“If the tree evolved to be in a certain situation in a certain environment, any departure from that slows down tree growth and stresses the tree more, which brings on pests and disease,” Black says. “If you keep it in the environment it evolved to be in, that’s the fastest, happiest state for production. It’s a numbers thing. That’s the name of the game for every single nursery, no matter what you’re trying to do. How fast can you produce that tree? Speed of production trumps everything.”

Maintaining that bare strip chemically is costly. You could send crews out with hoes, but that’s even more expensive. The very best solution, Black says, is to find something you can grow in that till strip, in the two feet on either side of your tree row. Growers should look for a cover crop that will grow in their area and crowd out weeds but also provide some service, some utility.

Black suggests two plants for two slightly different reasons: crimson clover and forage radish.

Crimson clover is an annual that can be sown in the fall. It germinates and crowds out all the other winter annuals. When it flowers and dies in late spring, it provides about 90 pounds of nitrogen per acre. That’s just what your young trees need, and the price of the clover seed is less than the price of nitrogen. Plus you receive weed suppression coming into the spring on winter annuals. That means only having to deal with summer annuals, which start being an issue right around the time you have time to think about weed control.

By having something growing in that tree row, you are also supplementing the soil with organic matter, which is hugely important to water and nutrient retention in the soil. Plus, the rooting action of that cover crop loosens up the soil. When the crimson clover plant dies, all of its roots die, too, and leave little spaces in the soil for air, water and tree roots to move around more easily.

If you take that decompacting objective to the next step, Black suggests not using crimson clover, but forage radish. The Daikon radish has a principal root the size of a forearm, and a tap root with a pencil diameter that goes down three or four feet below that. You sow it in the fall, it germinates and crowds out winter annuals. The soybean root sucks up any available nitrogen that the trees don’t need at that point, because they are shutting down for fall. After the first few nights when the temperature dips below 30 degrees, it reliably winter kills. Black says the southern states can’t use it, but the northern two-thirds of the U.S will have no problems. In the spring when the weather warms up, that tap root starts to rot and it releases all those nutrients out to the soil in the spring when the trees begin to grow.

“Plus you’ve punched an inch diameter hole 16 inches into the ground all over your tree rows without breaking any tree roots,” Black says. “It’s like subsoiling in and around existing trees. No diesel fuel, no big steel dragged around in the field; just the price of the seed.”

Cover crops are very region specific. Growers in Maine and Kentucky are going to have a different menu of cover crop options. Getting the menu is not difficult. The tricky part is getting the crops to germinate.

“For most of these crops, if you want a good stand going, you need to drill them in and you can’t pull a seed drill through your tree rows,” Black says. “Even if you had a narrow seed drill, you’d be hitting roots near the surface, you’d have prunings and surface trash everywhere. It’s an impossible environment for a seed drill.”

Black and his crew at Raemelton Farms tried to broadcast the seed to surface, but it needed perfect conditions for the crop to perform well. Their success improved when they switched to using a row mulcher.

“Millcreek makes a spreader that shoots the compost out sideways,” he says. “You drive down the row, you broadcast out the cover crop seed, then you come through with the spreader and top dress it with a light dusting of compost. Like a half-inch, works out to be 10 tons per acre. Compost hangs on to water very efficiently. You basically just mulched in your cover crop seed with something you can just spread over the top. By doing that we got phenomenal stand of both crimson clover, forage radish and a mix of the two.”

To learn more about possible cover crops in your area, contact your local university extension. Black says every extension service has people who are almost exclusively focused on cover crops for use with row crops like corn and soybeans. Your application may be new for them, but they can still help you. Once you get some ideas, start slow. Then, once you’ve determined what works in your specific area on your specific plants, scale it up for next year.