WHY USE COVER CROPS?
There are many reasons for organic farmers, gardeners, vineyard, and orchard growers to use cover crops over the winter months. The benefits are numerous! …
-As the local area around Sebastopol has typically heavy-clay soil, with low amounts of organic matter, N, P, K, CA, Su and other micronutrients, cover cropping is an ideal organic approach to adding all of these crucial components back into the our soil. Along with reliable compost, relatively low-cost ‘cover-cropping’ reduces or eliminates the need for more expensive and toxic (or potentially-‘hot’) amendments such as non-organic (i.e. conventional/chemical) fertilizers.
PLANTING A COVER CROP
Why plant a cover crop?
To put it simply, to help heal the earth and make it a better place for crop plants to grow. Cover crops can be the only practical method of supplying organic matter at high enough levels to maintain a high state of productivity. Organic matter itself is good for improving soil friability, tilth, and water penetration. Save time, fuel, and labor by mowing instead of discing and reduce soil compaction by fewer trips through the field.
As organic matter decays and forms humus, it can provide nitrogen and other soil nutrients for succeeding crops. The soil microorganisms that feed on cover crop residue contribute to a healthier soil ecosystem and help prevent plant diseases and nematode outbreaks. Erosion takes away valuable top soil containing important nutrients needed for plant growth. Even though you may not see any gullies or other visible forms of erosion, most bare land will erode with almost any amount of rainfall.
For severely eroded locations, Blando brome and Zorro fescue are probably the best as they both do well in poor fertility situations. As preventative measures, annual and perennial rye grass are much less expensive to seed but will grow quite a bit taller than Blando or Zorro. Grasses do a better job of holding soil than clovers due to having a dense root system but they are not deeply rooted and will not aid in the breakup of hardpan or allow much infiltration. There are many hillside vineyards who have planted a mix of annual grasses and annual clovers for erosion control with good success.
Vigor and moisture management can also be controlled by the cover crop chosen. Use low-water requirement covers such as Zorro or Mokelumne fescue when water needs to be conserved. When areas are too wet or competition with the crop is desired, use high water users such as perennial ryegrass or Calif. brome. Competition can shorten canopy growth and reduce leaf to fruit ratio to improve earlier sugar development and color.
Cover crops also have benefit as insectary plants for attracting and feeding beneficial insects. Cover crops have been found to drastically reduce spider mites.
Cover Crop Types & Varieties
In agriculture, a green manure is a type of cover crop grown primarily to add nutrients and organic matter to the soil. Typically, a green manure crop is grown for a specific period, and then plowed under and incorporated into the soil. Green manures usually perform multiple functions, that include soil improvement and soil protection:
* Leguminous green manures such as clover and vetch contain nitrogen-fixing symbiotic bacteria in root nodules that fix atmospheric nitrogen in a form that plants can use.
* Green manures increase the percentage of organic matter (biomass) in the soil, thereby improving water retention, aeration, and other soil characteristics.
* The root systems of some varieties of green manure grow deep in the soil and bring up nutrient resources unavailable to shallower-rooted crops.
* Common cover crop functions of weed suppression and prevention of soil erosion and compaction are often also considered when selecting and using green manures.
* Some green manure crops, when allowed to flower, provide forage for pollinating insects.
Historically, the practice of green manuring can be traced back to the fallow cycle of crop rotation, which was used to allow soils to recover.
Legumes are the preferred cover crop for green manure. They “fix” nitrogen from the air into a form readily available by plants. They are easily tilled or disced into the soil during spring and decay rapidly.
Legumes & Legume Blends
All the following legumes fix 70-150 lb. of nitrogen per acre per winter if disced in at 10% bloom and inoculated with Rhizobium bacteria at time of planting.
Legumes
(e.g. beans, peas, vetch and clovers) have roots that ‘fix’ (add) nitrogen (N) into the soil.
–Legumes as cover crops can be mowed (or scythed) and tilled into the soil in the spring (before planting of spring crops), which will add ample organic matter back into the soil. “Tilling under” of legumes should be done before flowers mature into viable seeds (while N remains within the softer foliar matter).
-Also there’s no need to irrigate (unless using perennial clovers) as we let the rain do the work!
Rich in varying ratios of legumes, the ‘Organic Matter Mazimizer’, ‘Organic Matter Builder’, and ’Green Manure’ Mixes are all popular for the above reasons. Inoculant (in small white bags) can be added to legume seeds just prior to planning to increase rhizobial activity in soil, increase N-fixing properties, and help the legumes’ uptake of vital nutrients from the soil.
Winter Growing
ANNUAL “RESEEDING” COVER CROP
Annual cover crops are recommended where organic matter is needed to increase humus levels and fertilizer availability, by providing conditions for beneficial soil microorganisms that cannot survive where soil organic matter is below 1.5%. Winter growing annuals are best for dry farmed perennial crops and gardens. Sow in the fall and turn under in the following spring.
Annual clovers
(aka ‘Subclovers’) for a dense low and spreading mat of nutrient-rich foliage, which when allowed to mature will form dormant seed pods, which dry in the summer months and re-seed themselves in the next autumn rains. Where/when irrigation is not provided after the rains cease, and when re-seeding is not desired, annual clovers should be used, to be tilled under to build organic matter, increase nitrogen and overall soil health.
Annuals for Permanent Cover
Most of the annual clovers are typically planted in the fall so they can take advantage of the winter rains. Most will not do well if planted at other times.
“PERMANENT COVER” CROP
Permanent cover crops are recommended where erosion control is needed or a permanent plant cover is desired to provide habitat for beneficial insects, better water infiltration and ability to move vehicles on the ground during the rainy season. Most permanent cover crops require at least some supplemental irrigation during the summer except for the annual clovers and summer dormant grasses. Also, they all require some mowing, especially in the first few years to help establish the cover crop.
Clover seed is inoculated with the appropriate Rhizobium bacteria for optimum nitrogen fixation.
Perennial clovers
(live Rose or Crimson) are often used in vineyard rows where tillage is not desired or required, but where irrigation will be provided after the rains have ceased (around Mar-June). Clover blooms will offer excellent forage for beneficial and pollinating insects, butterflies and honeybees!
*PLEASE NOTE: Clovers and Legumes will not release N-fixing nodules from roots if existing soil is low in Phosphorus! [When nodule’s inside is pink there is N-fixing occurring (good!) When nodule’s inside is white or grey, no N-fixing (not so good!)] To compensate for low ‘P’ in soil composition, apply adequate rate of (organic) Soft Rock Phosphate (SRP50).
TIPS FOR SUCCESS WITH CLOVERS
Make sure soil calcium and phosphorus levels are close to being adequate. Soil pH should be close to 6.0 or higher. Nitrogen levels are not critical. In fact, it is not recommended to give extra nitrogen to clovers or they will not work as hard to fix nitrogen. The most critical step with clovers is to TAMP THE SEED INTO THE SOIL ONCE BROADCASTED. If you drill the seed in with a Brillion seeder it will do the tamping for you. On a small scale, a lawn roller or jumping up and down on a sheet of plywood will work.
Perennials for Permanent Cover
Unless you live in a frost-free area, spring is the best time to plant perennials. While the plants stay green year-round, if watered, they basically go dormant when the ground gets cold.
PLANTING WILDFLOWERS
Fall is the time to plant these annual and perennial native and introduced wildflowers. For best results, remove weeds, then loosen top 1” of soil, level with a garden rake and scatter seeds evenly over the area. Mulch evenly with a fine layer of peat moss or compost 1/8” deep and water with a fine spray. After seedlings appear (which may take 2-6 weeks), water only as necessary. Once established, these wildflowers will bloom year after year, if you let them go to seed in the spring when they are done flowering.
Yellow Mustard
is grown prolifically in the Napa and Sonoma County winemaking vineyard regions. It is a permanent cover crop with a strong deep taproot which helps to break down poorer, clay soils, and adds a good deal of Nitrogen. ‘YM’ is also a member of the Brassica family, which has been shown be beneficial in preventing harmful nematodes when tilled under in vineyard rows. Negatively, YM may attract lacewings and other pest insects in areas close to streams, riparian zones…
Erosion Control
Barley, Red Oats, and Cereal Rye
can be used to help provide erosion control on sloped land, and for adding more Carbon and organic matter as well. The more variety of cover crops used the better!
Annual Rye Grass
Waning: DO NOT USE Annual Rye Grass in any area that is being prepared for growing spring crops i.e. as a cover crop. When tilled under or mowed, ‘ARG’ does not decompose into beneficial organic matter, but contains toxins, which damage microbial and overall soil health. For these reasons, only use ‘ARG’ for erosion control and/or early winter weed eradication measures in pasture of meadow areas where crops are not going to be grown!
Most grasses prefer a pH of 6.5 to 7.0. In this area, calcium is required and can be obtained from oyster shell lime and/or dolomite (if the pH is below 7.0) or gypsum (if the pH is above 7.0). Do not use dolomite if you have a heavy clay soil as it contains magnesium which is already at high levels in these types of soils here in the North Coast. Adding calcium is important for good plant growth, better water penetration through improved soil tilth, and disease resistance, and is especially important where chemical fertilizers have been used as they tend to make the soil more acidic.
We recommend fertilizing lawns with California Organic Fertilizer 7-5-7, at the rate of 3 to 5 pounds per 100 sq. ft. Two applications per year, spring, and fall, are sufficient with this slow-release fertilizer. See page 13 for complete pricing information on this fertilizer.
FALL FERTILIZING
Fall is an excellent time to apply slow-release organic fertilizers. Winter rains can be very helpful in taking these materials down to the root zone of plants additionally, soil microorganisms will begin decomposing them and making nutrients available for plant uptake in the Spring.
If you’re not sure how much of what to add, consider a soil test. Soil testing can tell you how much fertilizer you need to apply, rather than how much you think you might need! It is also useful for diagnosing problems with plant growth.
SOIL TESTS
1. THE BASIC SOIL TEST:
If your plants are doing OK, this will tell you all you want to know. Includes pH, % organic matter, estimated nitrogen release, phosphorus, potassium, calcium, magnesium, cation exchange capacity, cation base saturations for calcium, magnesium, potassium, sodium, and hydrogen. Not appropriate for compost, manure, or potting soil mixes (see below). We will also give you fertilizer recommendations based on the test results. This test takes about 2-3 weeks (10 -15 business days) for results to come back.
2. THE COMPLETE SOIL TEST:
If you have been experiencing problems with plant growth or yields, we recommend getting this test done. Includes the BASIC test values, plus trace elements sulfur, zinc, copper, boron, manganese, and iron. Not appropriate for compost, manure, or potting soil mixes (see below). Includes recommendations. This test takes about three weeks for results to come back.
Harmony Farm Supply offers all the above Cover Crops seeds in bulk, with standard discounts offered with quantities of each seed item over 50 lbs. Additionally, HFS offers many Wildflower blends (also in bulk, and ¼ lb bags) as well as two Beneficial Insect Blends which help attract beneficial and predatory insects to farms and vineyards. (Especially helpful in preventing lacewings and resultant ‘Piece’s Disease’). Remember, when you see ladybugs, butterflies, honeybees, spiders and/or earthworms, you most likely have a health garden, farm, or vineyard!