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How to Use & Grow Cover CropsANNUAL COVER CROPS Annual cool weather mixes or single varieties are usually planted with the intention of mowing or tilling at the end of their growing cycle. In your initial soil-building phase, you may choose to cover crop one or more areas intensively for a time, planting several annual mixes in succession. But simply growing a single cover will significantly improve your soil quality. Fall/winter cover crops are especially easy to add to your rotation because they make maximum use of winter and spring rains and reach their peak before field or garden space is needed for warm weather crops. For best germination, plant at least 4-6 weeks prior to your first hard freeze date. For your first fall/winter cover crop, it is good to use a mix, rather than relying on just one variety, so you can maximize your chances for a good stand and determine what grows well for you. For orchards and vineyards, start with our legume/oat blends. For homescale or commercial row crops, start with a fall rotation of our Soil Builder Mix. It was specially developed for general cool weather cover cropping, where temperatures do not drop below 20ºF. In Eastern or Midwestern areas with hard frosts, use our Cold Zone Soil Builder Mix. After cover cropping with a general mix you can consider whether individual annual varieties, alone or in combination, might be better suited to your specific situation. PERENNIAL COVER CROPS In orchards, vineyards, berries or other no-till irrigated growing situations, permanent perennial cover crops are a good choice. COVER CROPS FOR IRRIGATED ORCHARDS, BUSH BERRIES AND VINEYARDS Cool weather annuals are common for these situations. These are planted in the Fall in mild Winter areas and worked into the soil in Spring, after the cover crop has reached its maximum growth. WHAT IS A LEGUME? Legumes are alfalfas, clovers, vetches, peas, beans & other related plants. They are often used for cover cropping because they build (or "fix") Nitrogen in the soil. For maximum Nitrogen fixation, legume seeds must be "inoculated" or coated with a specific root bacteria. FERTILITY FOR COVER CROPS, EROSION MIXES AND PASTURE SEEDING The soil should be reasonably fertile prior to planting the seeds for these crops. The appropriate fertilizers should be broadcast and worked into the soil during ground preparation. Legumes and grasses grow best where there is an adequate to high level of available Phosphorus (P), Calcium (Ca) and Sulfur (S). If your soil tests or other factors indicate low levels of P, Ca or S, it is desirable to apply these nutrients prior to planting the seeds. The best organic materials for correcting these deficiencies are high quality aerobic Compost, Soft Rock Phosphate and Gypsum or Limestone. Compost will provide some P, Ca and S, as well as providing the soil with humus, humic acids, microbes and minerals. Rates to use should be determined by a soil analysis, but generally 2-4 tons per acre or home garden rates of 1 pound per 2-10 sq. ft. of high quality aerobically digested compost are adequate. Lower quality materials or raw manures will require higher amounts. Soft Rock Phosphate, a fine powdered material, will provide 16-20% P along with approximately 20% Ca. This material gives excellent results in all soil types, particularly when applied with compost. Gypsum will supply Calcium and Sulfur, as well as some trace elements. Limestone will add Calcium and raise the ph level of your soil. A lack of fertility will prevent you from obtaining the excellent stand you are attempting to establish. SOIL PREPARATION FOR COVER CROPS If you are fortunate enough to have access to a no till drill for planting, seedbed preparation can be fairly minimal, because the seeder will plant into almost anything. For the rest of us, soil preparation prior to planting is very important. Breaking up the soil reduces competition from weeds. Tillage also loosens the soil allowing the seedling roots to grow rapidly to reach moisture and provide anchorage. Tillage only needs to be as fine as the seeds to be planted. Fine seeded crops need a better seed bed than the large seeds like peas, beans, grains or vetch. BROADCAST SEEDING If using a broadcast seeder you will need to take extra precautions to insure a good stand of cover crop seeds. The soil should be disced, tilled or spaded prior to seeding, cover the seed to the correct depth. If using mulches to cover the seed please see the information on mulching. Because broadcast seeding does not bury the seed uniformly, you must use more seed to make up for the likelihood of poorer germination. The seed needs to be at the proper depth for good germination, resistance to drought and excess rainfall, to exclude bird predation and to preserve the viability of the inoculant which is on the seed. PLANTING DEPTH It is important to plant the seeds at the right depth in the soil. Too deep will inhibit germination, reduce seedling vigor and increase the risk of seed rot during and after germination. Planting too shallow will expose the seed to drying out between irrigations or rainfall, erosion by wind and water, or predation by birds and rodents. Generally, large seeds are planted at deeper depths because they have greater ability to push up though the soil than the small seed types. Small seeds, which have weaker emergence vigor, need to be planted quite shallow to obtain good germination. Poor germination and a poor stand is the common result from planting too deep. A good rule of thumb: if you don't know the optimum planting depth, plant the seed no deeper than 3 times the width of the seed. If you plant on the shallow side it is very important to keep adequate moisture near the seed to enhance germination. If the soil stays consistently moist during germination, then you'll have a better stand of plants. Keeping the soil irrigated also reduces the problem of crusting over, which can inhibit germination. LEGUME SEED INOCULATION A very important relationship exists between the legume plants and a group of soil bacteria commonly known as Rhizobium. This symbiotic relationship allows the bacteria to live on the roots of the legume plant, consuming carbohydrates from the plant and providing the plant with Nitrogen that the bacteria convert from gaseous soil Nitrogen to plant usable forms. Without these bacteria, legumes do not fix Nitrogen! Most soils do not contain very many, if any of these bacteria. In order to insure good Nitrogen fixation by the legume, it is necessary to inoculate the legume with the proper strains of the bacteria prior to planting the legume seeds. SEED STORAGE Seeds are living organisms that need reasonable care in order to insure their top performance. Store at temperatures between 40º-75ºF. Keep seeds dry and protect from freezing. MULCHING THE SEED INSTEAD OF PLANTING IN THE GROUND The seed should not be left exposed on the soil surface. Mulch should be placed only as thick as the normal planting depth as if sowing the seed into the soil. PLANTING IN DRYLAND (NON-IRRIGATED) CONDITIONS When planting cover crops where one is to rely on rainfall for germination, the germination rate will be radically affected by the timeliness or lack thereof of rain. Good soil preparation is important in these conditions to improve germination rates. Generally the seeds are planted at the deepest recommended depth to improve resistance to desiccation. PLANTING DATES FOR COOL WEATHER COVER CROPS, EROSION CONTROL MIXES, DRYLAND PASTURE AND ALFALFA Planting the seed at the optimum time is very important for success with these plants. The difference of a few weeks can make a large difference in crop performance. The best planting dates for the majority of United States to plant cool weather over-wintering plants such as cover crops, erosion control mixes, alfalfa and dryland pasture mixes are September 1 to October 15. In higher elevations or colder areas, August 15 to September 15 is optimum. The seeds need to germinate and make some growth while the soil is still moderately warm and the days have not grown short. Later plantings often have reduced germination rates and will make considerably less growth during the low light, low temperature days of Winter. They also tend to take longer to mature in the Spring thus requiring better Spring management. November, December and January plantings germinate slowly, if at all, don't compete well with weeds and do not grow nearly as well as the same seeds planted within the proper time window. If you must plant outside the optimum time for your zone, then it is necessary to increase the seeding rate by 25-50%, due to the expected low germination in the cool soils. On erosion control and pasture plantings, increasing seeding rate by 100-150% will increase the ability to get a good stand. Do not delay planting waiting for the rain. It is better to have the seed in the ground waiting for the rain than to plant after Fall rains begin. If possible, irrigation should be applied immediately after planting. The irrigation should be long enough to at least wet the soil to 1"-2" below the seeding depth, with 2-3 subsequent irrigations to supplement the early growth, if rains don't happen in Fall. The more growth these covers make in the Fall the better. PLANTING DATES FOR WARM SEASON COVER CROPS Warm season cover crops need to be planted after the soil has warmed to at least 60ºF and the likelihood of frost has passed. A good rule of thumb is to time the planting of the first warm season cover crops with the average corn planting date in your area, as they have similar requirements. INCORPORATING THE MATURE COVER CROP INTO THE SOIL The best time to till in your cover crop is when 50% of the flowers are in bloom. By turning in the cover crop while it is still lush, the cover will be rapidly decomposed by soil microbes who will then return nitrogen and other elements to the soil for the next crop. If the cover crop is shredded, the cover will break down faster. It is important to till the cover into the soil as quickly as possible after mowing, as the cover loses nitrogen and carbon to the atmosphere very rapidly if left exposed to the sun. For most cover crops, approximately 2/3 of the nitrogen in the cover crop is in the above ground portion. Depending on the quantity of organic material, the breakdown process will take 10-21 days if the soil is cultivated regularly. If the soil remains moist during this breakdown process, no additional water is necessary. However if the soil is dry when the cover is turned under or loses substantial moisture during the cultivating process, a light irrigation can do wonders to stimulate breakdown. HOME GARDENERS If it is too difficult for you to incorporate the cover crop, a second option would be to cut the tops at ground level and put the tops into the compost pile to break down into humus.
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