A well-managed growing space benefits significantly from fall cover cropping. After harvesting your garden vegetables, adding a fall cover crop can build soil, protect from soil loss, and assist in weed and pest control for the next growing season.
Read below to learn when to plant and how to manage cover crops for the maximum benefit of your growing space. Whether you have a small garden or a large high tunnel, implementing the practice of cover cropping that large scale farms use can dramatically improve your soil. Cover crops can even be used in container gardens to protect your soil over the winter and improve it for next year’s planting.
What is the purpose of planting a cover crop?
Growing cover crops will bring multiple benefits to your garden when planted at the right time and terminated properly. While all cover crops help to keep your soil covered, some will help with weed suppression through competition (radish, cereal rye), and some allopathically (cereal rye). Some cover crops will add to soil nutrition through nitrogen fixation (peas,clovers) others (tillage radish, cereal rye) will collect nutrients like nitrogen, and when winter killed, will release those nutrients, break up hardpan, and add organic matter to your garden as they decompose.
Selecting and Managing Cover Crops
When selecting a cover crop, consider timing and which crops you are planning to follow the cover crop. Another consideration is the time needed to manage the cover crop from preparing a seedbed through termination.
Cover crops, just like any crop, do require some seedbed preparation. While vigorous cover crops like rye and radish are sometimes broadcast seeded with no incorporation, the stand will benefit immensely from some minimal seedbed preparation (raking/ harrowing) before and after broadcast seeding. Seed-to-soil contact is important, and so is soil moisture. Your garden will benefit more from a healthy, competitive cover crop. If you have water available for your garden space, water your cover crop during periods without precipitation.
You want your cover crop healthy and growing a dense canopy. That way, as temperatures get cooler and growth is paused, or the crop is killed off by cold, you get maximum cover and competition for weeds. Some crops will winterkill and decompose into your soil, but the majority of fall and winter cover crops will require a termination the following spring. Common methods for termination of cover crops include crimping, mowing, and tillage.
Terminating a Cover Crop
The termination method is the most overlooked part of cover crop management. It is just as important and could be argued is even more important than growing the crop. Cover crops generally compete with weeds; while this is good, they can compete with vegetable crops. A well-done cover crop is terminated before seed maturation. Most cover crops are to be terminated at flower but sometimes may be terminated earlier in order to get a spring crop. The following is a list of non-chemical termination methods used extensively by growers of all scales.
Top 5 Termination Methods for Cover Crops
Crimping is a very useful termination method. This is a consistent crimping of the plants every 6 or so inches. A good solid crimp requires enough ground pressure to crimp stems in order to damage them enough that they have too many serious wounds to recover, and the end result is a nice flat mat of green mulch. Large-scale growers use roller crimpers, but that does not mean you cannot use this method much more affordably. Crimpers can be as simple as a 2-foot piece of angle iron attached to a 2x4 with a rope looped to each end so you can walk it along and press every six or so inches (shorter is better here because you want to get the most psi for your weight, roller crimpers have up to 75psi!) This method makes no-till planting large-seeded vegetables or planting out starts very enjoyable. The mat suppresses weeds and holds moisture well. What it doesn't do so well is encourage warming of the soil since it is covered by essentially a blanket of biomass
Mowing is another good form of cover crop termination that most are fairly familiar with. If the cover crop is mowed before seeds are produced, many cover crops will terminate after mowing. This is not a nice turf lawn mowing, you want to get good and low ( we are trying to inflict a mortal wound the plant cannot regrow from.) A mower comes to mind, and a mower is quite good at mowing, but you can successfully mow a cover crop in a smaller space with shears, a weed whacker, a scythe….essentially anything you can cut the stems with SAFELY.
Tillage is the third option that really does have its own benefits. If the cover has not gone to seed, tillage can terminate most crops. The thing that sets tillage apart is the fact that multiple cultivations or lighter tillage can also help clean up any weed survivors. Tillage will also expose bare soil, causing the soil to warm earlier in the spring, allowing earlier planting. The downfall is that there is no mulch to conserve water when the season heats up. Tillage can also save the day when a mowing termination is done too early, and the cover crop regrows or when mowing has not been as successful in termination as necessary. Tillage tools for termination could be as simple and small as a hoe up to a garden tiller or even a tractor with a plow or cultivator.
Livestock can also be used as a termination method for cover crops in enclosed spaces. If you have chickens, goats, or sheep, you can give them access to the cover cropped areas to eat down and dig up the crop. A combination of ruminates and birds is most effective. The goats or sheep will mow down the crop and provide manure. The chickens (or turkeys, guinea fowl, etc.) provide light tillage, eat any unsprouted seeds and pest larvae, and disturb the roots enough that most plants will not regrow. Chickens will also even out the planting surface as long as they are removed before they have time to start making dust baths. Poultry manure is great for the soil, but this method should not be used in areas where you plan to plant root crops or low-growing greens right away as it can contain pathogens. Check with your local ag extension office for guidelines on how long you need to wait after using chickens to plant certain crops in that space.
Winterkill as a termination method can be used in areas where temperatures drop below freezing for extended periods of time. Even though some cover crops do winterkill, this is not always complete termination. There will almost always be outliers of any grouping of enough plants, some may be hardier. Winter is different throughout the country, and good solid snow cover for a majority of the winter will help insulate cover crops from winter air temperatures and can lead to a much higher winter survival rate. Sometimes winter simply is simply not cold enough in regions of the country. These scenarios will require a termination plan. It is much easier to be prepared for a task and be let off the hook by nature than it is to scramble to have a response to the variability of the weather.
Using Silage Tarps After Cover Crops
There are a number of ways in which applying silage tarp after terminating your cover crop can dramatically improve the benefits that you will see from cover crop planting. Even as few as 4 weeks of tarping between termination and planting can provide many of the following benefits.
Tarps placed black side up will help to warm the soil for planting.
The added heat helps to decompose the plant matter faster. This makes more nutrients available faster.
Weed seeds, unsprouted cover crop seed from the original planting, and any seeds that developed before you terminated the crop will germinate under the tarp and then die off from lack of light.
Unterminated cover crops like winter rye that was mowed will be effectively killed from lack of light.
Tarps can also be used to protect cover crop seed from birds as it germinates. Just be sure to remove the tarps after about a week.
Let’s look at a few widely used cover crops, there are many more and some mixes that perform quite well together for multiple benefits. For a quick look at some of the benefits and potential candidates, I am just going to highlight a few that I prefer.
It would be quite difficult to make any sort of list or write about cover crops without mentioning CerealRye (Winter Rye), which is an impressive and deservedly well cover crop. Cereal rye is not to be confused with ryegrass.
Cereal rye is a small grain that can sprout and grow at very cool temperatures. This ability means it can be planted later than other cover crops and does a good job holding the soil together after harvesting later crops. It then overwinters and begins growth very early in the spring, outcompeting many weeds.
Cereal Rye also requires termination the following spring. Rye can be terminated early for a spring crop, but the thick mulch matt from crimping later on will not have grown yet. Cereal rye should be terminated in the boot stage or early heading stage if a heavy green mulch is desired. This is just before the seed heads emerge until just before flowering.
Tillage radish is a great cover crop for several reasons as well. As its name implies, tillage radish is a great choice for breaking up compacted soil and scavenging nitrogen. When the radish is winterkilled, it will decompose in the soil leaving behind scavenged nutrition and somewhat deep holes in the soil, allowing water infiltration and helping to make compacted soil loose and friable again.
Winter Pea or Field Pea is another good soil cover through the winter. They tend to grow quickly, making a thick mat of mulch and also fixing nitrogen in their roots to be made available when the nodules containing nitrogen decompose in your soil. They are a legume, and legumes can collect nitrogen from the air (our atmosphere is roughly 78% nitrogen) Field peas have quite variable winter survival rates based on weather, snow cover, and moisture, so be ready to terminate winter peas in spring.
Annual Ryegrass, Italian Ryegrass, is not to be confused with cereal rye. It is a cool season annual ( biennial in some climates), and it is a valuable cover crop for increasing soil water infiltration and covering bare soil through winter very well. It can be seeded later than most grasses and germinates very quickly (7-10 days.)
Although a fall cover crop, it does need 60 days before a hard killing frost to be able to grow enough for a good solid groundcover that will help prevent erosion. While it is considered an annual and it is not cold hardy, there may be some surviving annual rye in the spring that will need to be terminated before seeds mature by mowing, crimping, grazing, or multiple tillage passes.
The added bonus with annual rye is you can frost seed (plant when temperatures are going consistently below 40℉), so the seed can lay dormant. As the ground freezes and thaws in spring, the seed is worked into the gaps and cracks in the soil and can make good soil contact for germination.
Again, this is for after temperatures are going to stay cool but is most successful in the spring before your last frost. I have found somewhere in the neighborhood of 3-4 good hard freezes are required to get the soil contact your Annual Rye needs for the desired germination. I have had the greatest planting success during a late spring snowstorm with a broadcast spinner seeder.
When should I plant my fall cover crop?
Planting times for cover crops vary throughout the country. I would suggest contacting a local extension office, coop, FSA, and other local resources that can give you much more specific information. As a general rule, you need 6 or so weeks before a killing frost for any cover crop to get its biomass and root system robust enough to do some work for your soil.
Considerations when planting cover crops in a high tunnel
Extending the growing season with a hoop house also changes the way cover crops are managed. The hoop house may change your growing conditions enough that some cover crops may be planted later than would be suggested in an outdoor situation. The season extension can also cause poor to non-existent winter kill, requiring termination by the grower.
The other factor to consider is that with the ability to grow later into the fall/ winter and earlier in the spring, you may have a short window to grow a cover crop, which may become important in which cover crops you end up utilizing.
Depending on your operation, there may not be adequate time without a crop growing to really gain the benefits of a cover crop in your hoop house. There is a lot more involved in cover cropping than simply scattering some seed and walking away until spring planting time.
This article is a short intro to some of the variables you should consider about utilizing cover cropping in your weed management program in your operation. I encourage you to do research that is pertinent to your specific situation. There are many other cover crops out there, and while none are a magic bullet, they all come with benefits and potential complications to consider before planting.
Whether you are planning to open up a new gardening space, or if you want more information about the soil you are already using, a mason jar test and a quick reference to the soil pyramid chart can give you a lot of information about your soil.
When you have a limited amount of space to work with, it is best to focus on the crops that can have the biggest impact when paired with easy to store pantry staples. Read more about growing food in small spaces!