When is it Too Late to Seed Cover Crops?
If you’re a farmer, at some point you’ll likely experience a late harvest, whether it’s due to Mother Nature or an equipment problem. And if you plan on seeding your cover crops after your crops are off, you have the added challenge of trying to get them seeded in a timely manner. Depending on how late it gets, you may wonder whether it’s even worth seeding them at all.
It leads to the question: Is it ever too late to seed cover crops?
The short answer: It depends.
“Each situation is going to depend on the variables and conditions of that particular farmer,” says Wayne Ebersole.
The General Manager of cover crop seed company Future Generation Ag explains that your weather conditions, location, the number of acres you have, the species of cash crop you’re coming from and going to, as well as equipment, all play a role in determining whether it’s too late to get your cover crops seeded.
But the first factor to consider is when you want to benefit from that cover crop.
“It’s never too late to plant cover crops, but if you wanted the benefit in the fall and early winter, then it’s too late,” he says.
If you’re looking for benefits in the spring, as many farmers are, Ebersole says there are several species or mixes that can overwinter and still put on some growth in the spring.
The second factor to consider is your location. Leanne Dillard, Forage Agronomist at Auburn University, explains that in the Deep South, the closer you are to the Gulf of Mexico, the lower your probability of a cover crop stand failure because you have a lower chance of getting sub-freezing temperatures. But as you go north into the mountains and up through Appalachia, your probability increases.
“It’s a probability game and unfortunately it depends on that specific year,” Dillard says. “Usually we can’t forecast the weather, but if you look at the long-term forecast that NOAA puts out, that may give you a good indication of what that chance is.”
Grazed T-Raptor (brassica) and wheat cover crop mixture in Belle Mina, Ala., in November 2018. Leanne Dillard recommends growers who are using cover crops for forage get their covers seeded before Christmas. Photo by Leanne Dillard, Auburn University.
It also depends on what you want to achieve with your cover crop. A farmer looking to just having something growing out there for soil health benefits may be able to plant much later than a farmer who wants to produce nitrogen for his next cash crop or needs a lot of growth for forage.
When you plan on harvesting or terminating the cover crops will also play a role in how late you can seed. For example, if your next crop is corn and you plan to plant that in mid-April to early May, Dillard says seeding a cover crop in early February may be pointless because you won’t get much growth.
In general, Dillard recommends that those in the Southeast and Mid-Atlantic that just want to achieve some ground cover, have their covers seeded by Christmas. If the goal is to have enough growth for grazing, then they’ll need to back the date up a little bit to make it economically feasible.
“As with anything in farming, you have to roll the dice,” she explains. “But if you have a good idea of the long-term forecast being mild, then you can push that date, depending on latitude, to January 1st, maybe February 1st.”
Select Cold-Tolerant Species
Another factor with seeding cover crops late is the species you want to use. You may want to avoid any species that is not suitable for surviving cold weather, Ebersole says, such as radishes and some specific clover and oat varieties, although black oats have been known to overwinter south of I-70 and as far north as Pennsylvania. The USDA says that black oats will winterkill at temperatures less than 19 degrees Fahrenheit, depending on the growth stage.
Instead, Ebersole says wheat, triticale and cereal rye are some of the go-to species for late-seeding — according to Sustainable Agriculture Research and Education (SARE), cereal rye can germinate in soil temperatures as low as 34 degrees Fahrenheit, and needs at least 38 degrees to begin growing.
If you’re planning on planting corn, you may want to avoid cereal rye and stick with either triticale or a legume like crimson clover or hairy vetch. In fact, Ebersole says these species can survive longer when they’re planted late in far northern regions because the more growth they have, the more susceptible they are to cold weather. When seeded later, it’s not as big of a concern because they won’t have as much growth on them.
While it may not get as much growth as seen in this photo, cereal rye is one of the best species for seeding late, as it can germinate in cold temperatures. Photo by Stephen Ausmus, USDA Agricultural Research Service.
For those going into soybeans, cereal rye can be a very good choice, he says.
Dillard agrees that cereal rye would be best, but it’s also more expensive. If you’re planting late you should plan on using a cheaper variety, she says, so if it does fail the economic impact would be considerably less.
For those in southern regions that may not get temperatures as low as the Midwest, wheat is an inexpensive option that could work. According to the Government of Alberta Agriculture and Forestry department, wheat needs a minimum of 4 degrees Celsius (39.2 degrees Fahrenheit) but prefers 20 degrees Celsius (68 degrees Fahrenheit).
“Wheat is always a good versatile forage,” she says. “It has pretty good growth and cold tolerance.”
You could also use cover crop mixes because the chances of getting something growing are higher, as different species will tolerate different conditions, she says.
“Planting a mixture has more resilience under variable conditions than planting a monoculture,” Dillard explains. “You have more chance of having something germinate and be successful than if you were only o rely on one crop.”
One option would be a mix with brassicas, such as rapeseed, which are great at tolerating cold weather once they’re grown, but not when they germinate. However, Dillard notes that the seed is relatively inexpensive and the seeding rate is low, so including it in a mix doesn’t have a big economic risk.
“For most farmers my suggestion is, if you purchased the seed back in the fall, plant whatever you were planning on planting anyways,” she says.
Peas are another option because they can be more cold-tolerant than brassicas, but won’t provide a lot of growth because of the cold.
Ebersole notes that if you do seed brassicas or rapeseed late, it may not grow a deep taproot because they are a daylight sensitive plant and the days getting longer will cause them to go into seed production.
Plan to Drill
Dillard and Ebersole both agree that if you’re seeding your cover crops later, you should drill them over broadcasting.
Ebersole explains that if seed is broadcasted onto wet ground and sprouts, a hard freeze could kill the newly sprouted plants.
Another option is to frost-seed the cover crops, Ebersole says, but he still recommends using a drill for that over broadcasting.
Frost-seeding, which is typically done into pastures, uses the soil’s freeze-thaw cycle to get other plant species established. Growers typically broadcast their seed onto frozen ground, and as the soils thaw, the seed will get incorporated into the ground.
Frost-seeding with the drill is a similar technique. According to Ohio State University Extension, the drill will scratch the surface of the frozen ground to provide good seed-to-soil contact, and as the soil thaws, the seed trench will close up. They estimate that frost-seeding with a drill provides 25% to 50% better germination than broadcasting.
Ebersole recommends watching for a warmer day in the forecast that may allow for the top to thaw a bit and provide for better seed-to-soil contact.
If you’re drilling, you can plan on sticking to the same seeding rate you would have used if you were seeding the cover crops earlier in the year, Dillard says. Ebersole adds that if you typically seed on the lower end of a rate recommendation — such as 30 pounds of cereal rye vs. 60 — you could increase the seeding rate by 10%. And if you do decide to broadcast, he recommends increasing the seeding rate by 30%.
Consider Spring Management
If a cover crop was established late, Dillard says it’s likely not going to affect your termination plans — in fact, it might make them easier. With that said, if your cover crops typically help with weed suppression and they didn’t get as much growth, then you may need to use more herbicides to deal with increased weed pressure.
But if you’re looking to get a little more growth out of your cover crops before terminating them, Ebersole says you can try no-till planting your cash crop directly into them, also known as planting green.
“If you get very little cover crop growth and you terminate it before planting, that doesn’t help you with anything,” he says. “If that’s the scenario, you could try to plant green and then spray it out a day or two later before your cash crop comes out of the ground.”
Growers can let cover crops grow a little longer and get more growth out of them by planting green. They can also utilize a roller-crimper, as seen in the photo, to help terminate covers during planting. Photo by Jack Sherman, Rodale Institute.
This can help you get more benefit out of your cover crops, especially if you’re facing a wet spring, as letting the cover crop grow could help your ground dry out faster, he says.
But Ebersole adds you need to consider how comfortable you are with this practice.
“There have been times when it’s been dry enough to plant, so you plant green, then it gets wet and everything grows like mad,” he explains. “Then you’re struggling to get out there and get it killed.”
If you decide not to plant green, Ebersole recommends terminating the covers about three weeks before you plan on planting.
Always Be Prepared
The best way to set yourself up for success when seeding a cover crop late is to be prepared to go as soon as the opportunity presents itself. You’ll want to have your seed purchased and equipment ready before you need them.
“Even if you realize you’re not going to be harvesting anything until December, have everything ready,” Dillard says. “That way you’re ready to go the minute that it’s harvested. Because if you have to take the time to try to source the seed and get the drill, that can take several weeks.
“At this point, every day becomes a huge factor in determining whether it’s feasible or not. Make sure that everything is ready to go, so you can just flip the switch once the fields are harvested.”
Originally published at agfuse.com.