All About Cover Crops

Cover crops have one main purpose: to maintain soil health between growing seasons. They are placeholders not usually meant to be harvested or sold.  They improve the soil's structure and prevent erosion due to water and wind, factors that make tracts of land less useful for agriculture.

Cover crops are like mulch, and their presence increases nutrient levels, enhances biodiversity and moisture conservation, and keeps weeds at bay. In organic farms, cover crops add nitrogen back into the soil and can help manage pests and diseases.

Legume cover crops include vetch, peas and beans, and crimson clover. They fix nitrogen from the air, and you'll often need less fertilizer for your next cash crop when you use them. They're accommodating to beneficial pollinators and creepy crawlies, though.

Next, you have grasses. Fibrous grass root systems hold soil in place and increase organic matter in the ground to a greater degree than legumes. Grasses grow quickly and die quickly, too, when you need them to.

Finally, you have non-legume broadleaves like brassicas that can scavenge nutrients and tend not to be winter-hardy, so they're easy to control. "Cocktails" mix these cover crop type to multiply the benefits.

Here are just a few examples of oft-deployed cover crops.

• Red clover is a legume that grows best in cool, moist conditions but works on an extensive range of soil mediums. It can overwinter.
• Buckwheat is a broadleaf species and summer annual. It's the fastest-growing cover crop, a fantastic pollen source, and a weed suppressant.
• Oilseed radish is another common cover crop. It can tolerate mild freezing and prefers a clay loam soil type. There are no registered herbicides for this crop, so be careful not to let it establish viable seeds and spread.

Other than soil health, what do you hope the cover crop will achieve for your farm, and under what conditions will it grow?

These questions will inform the type of crop you pick. For example, cereal rye suppresses weeds when killed. Its decomposition also inhibits the germination of certain weeds. White clover can withstand winters in the Northeast, and buckwheat is heat-tolerant and suitable for warmer climates. The crop you pick needs to fit into your rotation schedule.

Efficient seed application isn't just for commercial seeds. Methods differ by crop. You can broadcast rye and wheat by air via a plane or by ground with seeders mounted on tractors, for example. The latter is the most accurate and popular method. Planting times also vary—you may need to do frost-seeding, interseeding, or pre or post-season seeding.

October is the season for cover crop seeding in the Northeast. If you're using cereal rye as a forage crop, aim for a seeding rate of 2 bu/ac. Lower seeding rates work for weed suppression during fall and for planting green.

Cover crops can help combat pathogens and waylay pests, but they can also encourage problems. Rodents and unwanted insects may make their home in the field, or diseases can take hold. Cover crops can become weeds if not chosen or managed correctly, so it's important to refer to best practices at every step.

When one plant grows for a season, it strips the soil of the nutrients it needed to flourish. Rotating crops is better than repeatedly growing the same crop in the same place and slowly leeching all the essential nutrients for that crop out of the ground.

It makes sense, then, that if you're using cover crops, you shouldn't plant a one that's too similar to your cash crop. Rotating your cover crops reduces pests and diseases. For example, you could switch between brassica, grass, and legumes in a three-year rotation, or swap between brassicas and legumes every other year.

Cover crop harvests don't have to be throw-away; you can use them as forage for grazing livestock. Diverse mixes of oats, peas, vetch, and other cover crops are cheap food sources and can be mechanically harvested for grazers.

If you're in the beef cattle business, you may be able to save on hay costs. Nutritional requirements differ between cattle classes, though, so you'll have to do the math for your farm.

Off-season grasses and cereals could help in the fight against climate change. Farming pulls carbon dioxide, the most well-known greenhouse gas, out of the atmosphere and stores it using a process called carbon sequestration. Plants use carbon dioxide in photosynthesis.

Farmers have been experiencing a series of weather disasters, and cover crops could make their fields more resilient to weather events like excessive rainfall and drought.

Cover crops can increase crop yields, even after just one year in rotation, although they're more likely to be a profitable long-term investment. They're not without risks but are seeing a resurgence thanks to funding promoting their use and encouraging farmers to give them a try.

The USDA Pandemic Cover Crop Program reduces crop insurance premiums if farmers invest in cover crops, and satellite imagery makes it possible to identify fields planted with them.