Cover Crops, Late Season

Many areas finally got decent rains, which opens up the possibility of seeding late summer and early fall cover crops. Good late season cover crops grow organic matter, scavenge any remaining nitrogen or other nutrients, choke out weeds, and make sure soil will not erode during fall and winter rains. Grains and grasses can provide all of these functions. Legumes can add additional nitrogen. Each has strengths and weaknesses. Below is a list of several good choices, depending on your specific goals and field conditions.

Rye is easily the most common cover crop used by growers in Massachusetts, and for good reason.  It is inexpensive, easy to get and establish, and can be seeded fairly late into the fall and still take.  It overwinters here and will continue to grow in the spring, producing lots of organic matter.  Rye may also be referred to as “winter rye” or “perennial ryegrass.”

Application.  Plant before September 15 if possible. Planting rye after September 15 dramatically reduces the ability of the roots to reach the available N in the soil and to produce enough canopy to protect soil from erosion. Cover crops planted in August develop larger, deeper roots and more canopy – providing better nitrogen uptake, less leaching, and more protection of soil from erosion. Seeding rate: 90 – 120 lbs/acre.

Oats can be seeded in the late summer or fall and will come up quickly, similar to winter rye.  Fall-planted oats grow some organic matter, crowd out weeds, prevent erosion, and provide winter-killed ground cover that is easily incorporated for early spring vegetables. Because it winter-kills and will not re-grow in the spring, it is easy to manage for early spring crops, and some growers prefer it over winter rye.  To maximize nitrogen provided to the following crop, mix oats with a legume that will overwinter, such as hairy vetch. Note that in winter 2011-2012 oats did NOT winter kill in many areas of New England. Be sure to check for winter survivors that need managing in spring.

Application.  Oats are more easily established than some other cover crops. Seed is usually easily and cheaply available. Make sure the oats have not been cooked (used as an animal feed); cleaned, bin-run seed is fine.  Prepare a weed-free seedbed from mid-August – mid- September. Try to seed by Sept. 1 or no later than 40 days before killing frost. Growers along the coast can plant later.  For seeding after vegetables, or when using oats as a nurse crop with legumes, no nitrogen fertilizer is required. Drill 80-110 lb/A oats; broadcast 110-140 lb/A. Increase the rate 10% in late September. When seeding oats with a legume use a lower rate of oats (for hairy vetch or clover, 35-75 lb/A is appropriate). Soil crusting after heavy rain will affect the stand and the cover crops may require reseeding.

Ryegrass is used by some growers because of its thick root system that is thought to mop up more nitrogen than rye or oat.  It makes a dense sod which improves soil aggregation and reduces surface soil compaction.  While ryegrass seedlings look weak compared to wheat or rye, they grow rapidly and are good for fall weed suppression.
Ryegrass is a species closely related to rye, but it is an annual, while rye is a perennial.  Because the two plants are related, rye is sometimes referred to as “perennial ryegrass” and ryegrass as “annual ryegrass,” which can cause confusion.  Despite these designations, “annual” ryegrass may overwinter and “perennia’l rye may winterkill --depending on when you seed them.  Some varieties of “annual” ryegrass are also more resistant to winter-kill than others.  If you have not seeded them before and would like to evaluate a particular variety, plant a little in order to see its growth habit.  Ryegrass can also be used as a cover crop in the early spring.  The seed is small and light, so specialized equipment will be needed if seeding a large area.

Application.  Ryegrass should be planted from late August to mid-September. For weed control, rapid and vigorous growth is essential, and dependent upon good soil moisture and adequate nitrogen. There is often enough nitrogen left in the soil after vegetables. If there is not, 30 lb/A of N can double fall growth of the ryegrass. Under dry conditions, drilling is necessary. If the soil surface is moist, broadcasting without covering is effective. Seed ryegrass at 10 lb/A if drilled into reasonably moist soil, and 15 lb/A in dryer soil. Broadcasting requires 15-20 lb/A.

In the spring, leave plenty of time for the ryegrass sod to decompose after tillage or herbicide application. Don’t plan on planting an early vegetable crop after it. Glyphosate is not effective until average daytime temperatures have reached the 50s and the ryegrass is actively growing. Ryegrass volunteers are particularly undesirable in small grains, so special care must be taken if they are part of your rotation.

Winter Wheat is a crop of increasing interest both as a cereal grain and as a cover crop. It is easier to manage in the spring compared to winter rye; it does not grow as tall or mature as quickly so there is no rush to kill it in early spring and risk compacting soils. Wheat is excellent for erosion control, for scavenging N, P and K in fall (takes up N slowly in fall, heavily in spring), suppressing weeds in spring and fall, and building soil organic matter and tilth. In spring, it can be grazed or tilled under. Best growth will be in well-drained soils with moderate fertility; wet or heavy soils are tolerated but flooding is not. Rye is a better choice on poor soils.

Application.  Plant in late summer to early fall, before mid-September. As a cover crop, use 60-120 lbs/A if drilled or 60 to 160 lb if broadcasted. Seed depth should be about ½ to 1.5 inches. Wheat also works well as a nurse crop for legumes such as hairy vetch or clover, either fall seeded or frost seeded in spring.

Buckwheat establishes quickly and provides a weed-smothering canopy within two to three weeks. It is one of the best cover crops for filling a short niche during the growing season.  It scavenges phosphorus from soil and makes it available to subsequent crops. It does well in poor or worn-out soils and newly tilled land, likes light or sandy soil, but does not grow in wet heavy soils. The dense fibrous roots take up nutrients and leave top soil loose and friable. It is easy to incorporate. If mowed before 25% bloom it will re-grow. Pollinators as well as natural enemies of insect pests thrive on the shallow white blossoms. It is frost sensitive and will winter kill. An important caution: buckwheat can become a weed. Kill within 7 to 10 days after flowering begins, before the first seeds begin to harden and turn brown. Earliest maturing seed can shatter before plants finish blooming. Some seed may overwinter in milder regions.

Application:  Drill at 50 -70 lb/A, 0.5 to 1.5 inches deep or broadcast at 60-100 lb/A on a firm seedbed and disk or tine lightly.  If left to overwinter, it can provide adequate soil cover with easy spring management, but it may be best used to fill a window between early and late crops.

Sorghum-sudangrass hybrids (sudex) is one of the best for building organic matter, penetrating and loosening compacted layers in subsoil competing with weeds. If left to overwinter, the dead residue protects soils and is easy too manage in spring. It provides the most organic matter for the cost of seed of any cover crop.

Application.  This cover crop establishes and grows best in hot weather; for the best biomass production, it is best to seed before late August.  However, it can still be planted later and will grow until frost-killed, which may be well into October in some years and locations. Drill seed 35-40 lb/A at 2 inches deep if needed to reach moist soil, or broadcast at 40-50 lb/A. Mowing at 3-4 feet stimulates root depth (from 6-8 to 10-12 inches) and root mass as well as production of more tillers. Incorporate while green to obtain nematode suppression.

Legume cover crops: hairy vetch and red clover - If well managed, legume cover crops can provide good quantities of nitrogen to the following crop. Hairy vetch and medium red clover are both reliable and economical options. Hairy vetch over winters and has the potential to fix up to 150 lbs/A nitrogen. Most of the nitrogen is fixed during May, however, so seed it where a mid-June cash crop planting will go.

Application.  Mid-August through early September is the best time to establish a legume cover crop. Vetch seedlings grow slowly so get it planted by September 15th to give it time to develop a strong root system to ensure over-wintering.  Vetch needs to be drilled into a soil with good moisture for a reliable stand.  Seed it at 40 lbs/A and be sure to inoculate to ensure N fixation. (Vetch can be sown at rates as low as 25 lb/A, but the additional weed suppression and N fixation from the higher rate can make it cost effective.) Vetch should be seeded with a grass nurse crop to reliably overwinter. The grass will also reduce weed growth and will provide support to reduce matting of the vetch under snow. Wheat (40 lb/A) overwinters and is likely the best nurse crop in most situations, although oat (40-50 lb/A) and rye (30-40 lb/A) can also be used.  The vetch and grain seed can be mixed together in the drill. In the spring incorporate at early bloom of the vetch, typically late May, for maximum N fixation and minimum vetch seed production.  Medium red clover is sown at 8 to 10 lbs per acre if drilled and 10-12 lb/A if broadcast or sown onto prepared ground. Clover be overseeded at the last cultivation in fall crops, or seeded with a nurse crop of small grain. Clover may be incorporated in spring or allowed to grow through a full season. Allow a couple of weeks for breakdown before planting your vegetable crop.
Caution: If you raise small grains don’t plant hairy vetch. It has hard seed that will germinate in future small grains producing vetch seed that contaminates the grain.

Note: Seeding rate recommendations may vary with regional differences.
For seed sources, costs, and more details on these cover crops go to the Cover Crops for Vegetable Growers website at: http://covercrops.cals.cornell.edu/ Scroll down the left menu for the various crops.

- adapted from articles by R. Hazzard & F. Mangan, UMass; and Carol MacNeil and Thomas Bjorkman, Cornell Vegetable Program (see http://covercrops.cals.cornell.edu/). Resources: Managing Cover Crops Profitably, 3rd edition, published by Sustainable Agriculture Network available in hard copy and online; New England Vegetable Management Guide, http://nevegetable.org/.