Danielle Treadwell, University of Florida
Adapted from: Treadwell, D., W. Klassen, M. Alligood, and S. Shewey. 2008. Annual cover crops in Florida vegetable systems Part 3. Buying and sourcing. HS1142. Institute of Food and Agricultural Sciences, University of Florida, Gainesville.
Demand for cover crop seed is greater than ever. Organic producers who desire to reduce production costs and conserve natural resources are increasingly turning to cover crops as a method to accomplish those goals. This demand has encouraged research and breeding efforts on cover crop species. Seed sold in the U.S. is produced domestically as well as abroad. Winter annual cover crops including legumes and cereal grains are produced mostly in the northeast and in Canada. Many tropical summer legumes are produced in Hawaii, and some varieties of tropical legumes may come from Asia, India, and South America.
Figure 1. Oat 'Saia' cover crop. Photo credit: Mikio Miyazoe, Oregon State University.
The National Organic Program regulations on annual seeds, including cover crop seeds, state that organically grown seeds must be used, when commercially available (CFR 205.204). If a grower can demostrate to the certifying agent that organic seed was not available, conventionally-grown, untreated seed can be used. Many commercially available cover crop seeds have been treated with prohibited substances such as a synthetic fungicide, but in many cases untreated seed is available. Fungicide- or insecticide-treated seeds may not be used by organic producers.
Nonorganic, untreated seeds can be used as a last resort in the following situations:
Treated seeds can be used in the following situations:
Producers who plant nonorganic untreated seed must provide documentation to support why organic seeds were not planted. Documentation typically includes a written account of at least three attempts (phone calls, written requests) for organic cover crop seed to support a substitution. Treated seed use must be supported by documented evidence of that use of the treatment was required under Federal or State phytosanitary regulations. Organic producers are required to save all seed labels for their records. As always, producers must get approval from their certification agency before making any changes or substitutions to their organic system plan (farm plan). Contact information of some seed suppliers that provide organic cover crop seed are identified in Table 2. For more information, see Sourcing Certified Organic Seed and the National Organic Program Regulations.
Organic producers are prohibited from planting seeds and planting stock grown using "excluded methods." The NOP defines "excluded methods" as, "A variety of methods used to genetically modify organisms or influence their growth and development by means that are not possible under natural conditions or processes and are not considered compatible with organic production. Such methods include cell fusion, microencapsulation and macroencapsulation, and recombinant DNA technology (including gene deletion, gene doubling, introducing a foreign gene, and changing the positions of genes when achieved by recombinant DNA technology). Such methods do not include the use of traditional breeding, conjugation, fermentation, hybridization, in vitro fertilization, or tissue culture."
Some retailers offer seed with claims that it is free of genetic material created by genetic engineering biotechnologies. The claim typically reads “GMO-free,” meaning seeds are free from genetically-modified organisms (GMOs). Laboratory tests can detect genetically modified seed. If producers desire to have GMO-free seed, they should contact the retailer and request documentation for the claim. Several federal agencies are involved in the regulation and oversight of GMO seed and other agricultural products. Product claims of GMO-free are not regulated by the federal government.
There are many advantages to planting cover crops, such as reduced erosion, enhancement of biological control, and nutrient cycling. There may also be disadvantages, including additional production costs, delays in planting vegetables, increased pest occurrence and nitrogen immobilization. Most of these disadvantages can be avoided with a little research, good planning, and sound execution.
Cover crop costs and benefits should be evaluated based on the degree to which the cover crops fulfill agroecosystem services and production objectives. The complexity of cropping systems that include cover crops can make it extremely difficult to assign a dollar figure to the benefits, particularly those that are achieved in the long term. In one recent analysis of cover crop benefits and costs, cereal cover crops as a group were best suited to increase soil organic matter; legumes were best suited to provide nitrogen, while brassicas were most effective at controlling a wide spectrum of soil pests (Snapp et al., 2005).
The cost of seed will be influenced by the country of origin and the distance it must travel to get to your address. The cost per pound of cover crop seed is most often very reasonable for the ecological services cover crops provide (Snapp et al., 2005). A pound of winter annual rye typically costs between 75 cents to $2.00 a pound. When seeded to 50 pounds an acre, the cost ranges from $38 to $100 per acre.
When purchasing legume seeds, it is important to also purchase the correct inoculant. Inoculation is the application of specific nitrogen-fixing bacteria to the seeds before planting. Inoculation is allowed for organic production, so long as the inoculant is not genetically engineered.
The cross-inoculation groups of most of the field and forage legumes commonly grown are tabulated in the University of Florida IFAS Extension publication Nitrogen Fixation and Inoculation of Forage Legumes by Adjei et al. (2006). These nitrogen-fixing bacteria attach to roots of legumes and convert nitrogen gas from our atmosphere to a form of nitrogen that the legume can use. A summary of recommended inoculants for legumes is provided in Table 1. Inoculants are an inexpensive way to ensure a good stand and improve the efficiency of nitrogen fixation. They can be mixed in dry with cover crop seed before planting, but research indicates an improvement in nitrogen fixation is attained when a sticking agent is used (Clark, 2007). A mixture of 10% sugar syrup and water can be added to the cover crop seed prior to adding inoculant for improved contact and retention. The inoculant contains live organisms; therefore, do not expose inoculant to direct sun or excessive heat. Store inoculant in the refrigerator and use before the expiration date. Contact information for inoculant retailers is provided in Table 2.
|Legume||Recommended Inoculant Group(s)|
|Cowpeas or Lespedeza|
|Crimson or Berseem|
|Pea or Vetch|
|Red clover or White clover|
|Subterranean clover||Subterranean clover or Clover or Rose|
|Sweet clover||Alfalfa or Sweet clover|
|Sunn hemp||Cowpea EL (based on Abdul-Baki et al., 2001)|
|Velvetbean||Cowpea EL (based on Piper and Morse, 1928)|
Popular cover crops such as sorghum-sudangrass and cowpea have many named varieties and are widely available at local feed and seed stores and national seed retailers such as Johnny’s Seeds. Frequently, seeds of these varieties are treated with a fungicide to prevent seed-born diseases, but vendors are often very accommodating and with advance notice they will work with suppliers to reserve seed prior to treatment. Certified organic cover crop seed is becoming increasingly available, but demand is greater than supply and therefore seed can be expensive.
Cover crops with emerging popularity such as velvetbean and sunn hemp can be difficult to locate in large amounts. Many cover crops are sold as unnamed cultivars and are available from a limited number of sources. National retailers specializing in open pollinated seed are a good source for unnamed cultivars. Awareness of the diversity of cover crops has been facilitated by research efforts at universities and by innovative producers. However, cover crop breeding efforts at universities and private industries are sporadic. Perhaps, if demand for cover crops increases, there will be increased motivation to invest in research and development for crop improvement.
For small farmers, a number of seed saving and exchange organizations can facilitate the search for specialty seed. In addition to the retailers listed in Table 2, there are a number of additional organizations (many are not-for-profit) that will provide certified organic seed, including Educational Concerns for Hunger Organization (ECHO), and Seed Savers Exchange. Additional resources include local seed and feed retailers, local Natural Resources Conservation Service (NRCS) offices, and area farmers.
|Seed Company||Products||Contact Information|
|Adams-Brisco Seed Co., Inc.||Treated seed
Untreated seed upon request
|325 East Second Street
PO Box 19
Jackson, GA 30233-0019
Phone (770) 775-7826
Fax (770) 775-7122
|C. M. Payne and Sons, Inc.||Specialize in forage legumes||Sebring, FL
Phone (941) 385-4642
|Diamond R Fertilizer||Treated seed
Untreated seed upon request
Custom seed mixes
|321 N. Hennis Rd.
P.O. Box 12489
Winter Garden, FL 34787
Phone (407) 656-3007
Contact information for all locations available online:
|Haile-Dean Seed Co.||Treated seed||501 N. Hennis Rd.
Winter Garden, FL 34787
Phone (407) 877-3333 or (800) 423-7333
|Mixon Seed Company||Treated seed||P.O. Box 1652
Orangeburg, SC 29116-1652
Phone (803) 531-1777 or (800) 922-1377
Fax: (803) 534-5027
|Sawan Seeds, Inc.||Treated seed||P.O. Box 188
Pelham, GA 31779
Phone (229) 294-4953 or (800) 423 7333
|Southern States||Treated seed
Untreated seed upon request
|Contact information for all locations available online:
|Wise Seed Company, Inc.||All Untreated seed||930 Highway 630 West
Frostproof, FL 33843
Phone (863) 635-4473
Fax (863) 635-4880
|Wolf & Wolf Seeds||Organic seed
|541 South Orlando Ave., Suite 207
Maitland, FL 32751
Phone (407) 481-0810
Fax (407) 481-0840
|Fedco Seeds||Untreated Seed||PO Box 520
Waterville, ME 04903
Phone (207) 873-7333
Fax (207) 873-7333
|Johnny’s Selected Seeds||Treated Seed
|RR 1 Box 2580
Albion, ME 04910
Phone (800) 738-6314 or (207) 437-4395
|North County Organics||Untreated seed
|PO Box 372
203 Depot Street
Bradford, VT 05033
Phone (802) 222-4277
Fax (802) 222-9661
|Organic Growers Supply||Untreated Seed
|PO Box 520
Waterville, ME 04903-0520
Phone (207) 426-2066
Fax (207) 872-8317
|Western and Mid-western Retailers|
|Albert Lea Seedhouse, Inc.||Treated seed
|PO Box 238
Albert Lea, MN 50007
Phone (800) 352-5247
Fax (507) 373-7032
|Bailey Seed Company||Untreated seed
|PO Box 13517
Salem, OR 97309
Phone (800) 407-7713 or (503) 362-9700
Fax (503) 362-1705
|Bountiful Gardens||Untreated seed||18001 Shafer Ranch Road
Willits, CA 95490-9626
Phone (707) 459-6410
Fax (707) 459-1925
|Buckwheat Growers Assoc. Of Minnesota||Untreated seed
|PO Box 492
206 Aldrich Avenue SE
Wadena, MN 56482
Phone (218) 445-5475
Fax (218) 631-9212
|EMD Crop BioScience (formerly Nitragin, Inc.)||Rhizobial inoculants||13100 West Lisbon Avenue
Brookfield, WI 53005
Phone (262) 957-2000
Fax (262) 957-2121
|Harmony Farm Supply & Nursery||Untreated seed
|PO Box 460
3244 Hwy 116 N
Sebastopol, CA 95472
Phone (707) 823-9125
Fax (707) 825-1734
|Kauffman Seeds||Treated seeds
|7508 S. Mayfield
Haven, KS 67543
Phone (620) 465-2245 or (800) 634-2836
Fax (620) 465-3565
|Midwestern Bio-Ag||Untreated seed
|Box 160 Highway 1D
Blue Mounds, WI 53517
Phone (800) 327-6012
Fax (608) 437-4441
|Planet Natural||Untreated seed
|1612 Gold Avenue
Bozeman, MT 59715
Phone (800) 289-6656
Fax (406) 587-0227
|Peaceful Valley Farm Supply||Untreated seed
|PO Box 2209 110 Spring Hill Drive
Grass Valley, CA 95945
Phone (530) 272-4769
Fax: (530) 272-4794
|Territorial Seed Company||Untreated seed||PO Box 158
Cottage Grove, OR 97424-0061
Fax (888) 657-3131
In summary, integration of cover crops in a cropping system can have significant ecological impacts on the cropping system including crop establishment, nutrient availability, biodiversity enhancement, and pest occurrence. Producers have many options in cover crop species selection and management, and objectives will be dictated by producer needs and production constraints. Cover crop management does require some pre-planning, but the contributions to the farming system can be very beneficial. A plan for planting, mowing and termination are needed to avoid delays and costly errors. If you decide to try something new, be sure to ask about seed size and shape to determine if the seed is appropriate for the planting equipment on your farm. Experiment with a few well-selected species in an area large enough to accommodate the equipment you plan to use before implementing cover crops on the whole farm, if you are new to cover crops.
This is an eOrganic article and was reviewed for compliance with National Organic Program regulations by members of the eOrganic community. Always check with your organic certification agency before adopting new practices or using new materials. For more information, refer to eOrganic's articles on organic certification.