EM 8701 January 1998 50¢

RED CLOVER (Trifolium pratense) R. Sattell, R. Dick, D. Hemphill, and D. McGrath

Red clover is an herbaceous concentrations of estrogen-like colonized by an appropriate strain of perennial or biennial legume with compounds may cause infertility. rhizobia bacteria to be able to erect, leafy stems that originate from Red clover residues can supply convert atmospheric nitrogen into a thick crown and terminate with a significant amounts of nitrogen (N) to plant-available forms. Inoculating flower head. Height at maturity is subsequent crops, and the large, seed with the proper rhizobia about 2 feet. deep taproot is effective for loosen- bacteria ensures that the bacteria will Leaves are composed of three ing soils and cycling nutrients to the be presentDATE. when the seed germi- oblong leaflets that usually have surface. Vigorous spring growth is nates. light-colored “V” markings at their effective for suppressing weeds. Use fresh inoculant, protect it from center. Both leaves and stems usually OFheat and light, and apply it to seeds are hairy. Dry matter and N accumulation just before planting according to the Flowers are pink-purple or In a 5-year trial in the mid- manufacturer’s directions. Cover magenta. Seeds are small (approxi- Willamette Valley, ‘Kenland’ red broadcast seed with soil to protect mately 240,000 seeds/lb), oblong, clover planted in mid-September inoculant from sunlight. and yellow, reddish-brown, or dark accumulated a maximum OUTof 3.3, mini- You may not need to inoculate if gray. mum of 0.2, and mean of 1.7 tons the appropriate rhizobia bacteria Red clover has a branched taproot dry matter/acre, and a maximum of already are present in the soil. You and extensive surface roots. 168, minimum of 10,IS and mean of 83 can find out by planting a section of When used in annual rotations, fall lb N/acre by mid-April. the field with raw (non-inoculated) and winter growth is slow, but spring seed and watching for differences in growth is rapid. Management growth. Suggested fall planting dates are When relay interplanting, broad- Environmental preferences from mid-September through early cast seed into a standing vegetable and limitations October, or earlierinformation: if irrigation is crop before the final cultivation. Red clover grows well on loams, available or soils are moist. Increase irrigation frequency to keep silt loams, and sandy loams as well as Seeding rates for use as a cover the soil surface moist until the clover on clayey soils. It can survive winter crop vary from 15 to 25 lb/acre. Drill is established under the summer crop temperatures as low as -30°F and seed into a fine seedbed at a depth canopy (about 2 weeks). 1 tolerates temporary waterlogging, but of ⁄2 inch for best stand establish- cannot survive prolonged waterlog- ment. Alternative ging or flooding. The optimum pH seeding methods Quick facts: Red clover range is 6.6–7.6, but a range of 4.5–currentthat can reduce 8.2 is tolerated. PUBLICATIONseedbed prepara- Common names Red clover tion but require Hardiness zone 4 (see Figure 1) Uses higher seeding pH tolerance 4.5–8.2; optimum near 7.0 Red clover is used successfully in rates are: drill into Best soil type Wide range Oregon as a fall-plantedmost cover crop a rough seedbed Flood tolerance Moderate andTHIS green manure in rotations with prepared by Drought tolerance Moderate vegetable crops. It also is used as a disking, or Shade tolerance Moderate broadcast over a relay interplanted cover crop Mowing tolerance High if mown higher than 5 inches For rough or smooth (i.e., planted into a standing crop) Dry matter accumulation 1.7 tons/acre and makes excellent forage, hay, seedbed and then N accumulation 85 lb/acre and silage, although it should not disk lightly to http://extension.oregonstate.edu/catalogN to following crop Half of accumulated N be used as sheep pasture during cover seed. breeding season because its high Red clover Uses Use as relay-interplanted or winter annual cover crop in rotations, or as a cover in roots need to be orchards to smother spring weeds, fix N, and improve soil tilth. Often grown with cereal grains. Tolerates frozen soils. Cautions May become weed in annual crop rotations. Red clover has performed well clover stems begin to grow confers a majority of red clovers sown in when relay interplanted into short- competitive advantage to the clover. Oregon. They produce tall, erect statured crops. When relay inter- Red clover can be killed with an flowering stems with leaves at the planted into tall-statured crops such appropriate herbicide. Consult your nodes, the spring after they are as sweet corn, intense shade, heavy county agent of the OSU Extension planted. Although they are perenni- harvest residue, and harvest traffic Service for herbicide recommenda- als, early flowering red clovers most result in patchy stands. However, red tions. Follow all label restrictions. often are treated as winter annuals clover appears to be better adapted (turned under or killed in spring) to these adverse conditions than the Pest interactions when used as a cover crop. Seed vetches, peas, or crimson clover, Red clover is not an appropriate often is marketed simply as “Medium accumulating as much as cover crop to grow in rotation with a Red clover” and, if locally produced, 1 1 ⁄2 tons dry matter/acre and 80 lb cash crop legume because they are may be well adapted. N/acre by the end of April in the susceptible to many of the same ‘Kenland’ red clover has been Willamette Valley. pathogens, allowing pathogen used successfully in the Willamette In western Oregon, red clover populations to grow quickly. Valley as both a fall-planted and generally is allowed to grow until at Incorporation of succulent red relay-interplantedDATE. cover crop. It is least mid-April, because nearly all dry clover residues often causes a sharp resistant to Sclerotinia crown rot and matter and N accumulation occur in increase in soil-borne pathogen is tolerant of waterlogged soils. spring with the onset of warm populations, especially damping-off OF‘Kenland’ red clover is nearly dor- weather. Incorporating red clover fungi (e.g., pythium). If susceptible mant during late fall and winter but residues approximately 3 weeks seed is planted shortly after incorpo- grows rapidly in spring with the before the summer crop is planted ration, you may have more problems onset of warmer temperatures. maximizes red clover spring growth with disease. Avoid this problem by while minimizing pythium problems waiting several weeks betweenOUT For more information (see below). residue incorporation and planting, World Wide Web When grown alone, red clover’s and by ensuring that soil temperature Orchard floor management informa- succulent residues are incorporated and seedbed preparationIS are optimal tion—http://www.orst.edu/dept/hort/ for rapid summer crop seedling weeds/floormgt.htm easily with a moldboard plow or disk OSU Extension Service publications— emergence. and decompose very rapidly, releas- eesc.orst.edu ing part of the accumulated N for use Varieties/cultivars The University of California, Davis by the following crop. cover crop information—http:// Red clover often is planted with a Cultivated red clovers are grouped www.sarep.ucdavis.edu/sarep/ccrop/ cereal grain companion crop that is as early flowering or late flowering types. ‘Mammothinformation: Red’ is one of the Oregon Cover Crop Handbook able to scavenge N and protect the This publication also is part of Using soil during fall and winter. Plant most common late flowering, or single cut, varieties, and is used at Cover Crops in Oregon, EM 8704, which companion crops at approximately contains an overview of cover crop usage one-half, and clover at two-thirds, of high elevations or where the growing and descriptions of 13 individual cover their monoculture seeding rate. If the season is short. It is a winter-hardy crops. To order copies of EM 8704, send companion crop is too dense in biennial that grows in a round clump your request and $5.50 per copy to: spring, grazing or clipping it before without flowering stems the first year. Publication Orders currentThe early flowering types, also Extension & Station Communications PUBLICATIONcalled ‘Medium Red’ or double cut Oregon State University (because they can be cut several 422 Kerr Administration times in a year for hay), comprise the Corvallis, OR 97331-2119 most Fax: 541-737-0817 THIS © 1998 Oregon State University. This publication may be photocopied or reprinted in its entirety for noncommercial purposes.

Robert Sattell, faculty research assistant in crop and soil science; Richard Dick, professor of soil For science; Delbert Hemphill, professor of agriculture; and Dan McGrath, Extension agent, Willamette Valley; Oregon State University. Figure 1.—Oregon http://extension.oregonstate.edu/catalogplant hardiness zone Funding for this project was provided by the Oregon Department of Agriculture. map. Red clover normally will survive in This publication was produced and distributed in furtherance of the Acts of Congress of May 8 and Zone 4 or any warmer zone. (Extracted June 30, 1914. Extension work is a cooperative program of Oregon State University, the U.S. from the USDA’s national plant hardiness Department of Agriculture, and Oregon counties. Oregon State University Extension Service offers zone map, based on average annual educational programs, activities, and materials—without regard to race, color, religion, sex, sexual minimum temperature in °F.) orientation, national origin, age, marital status, disability, and disabled veteran or Vietnam-era Zone 4 = -30 to -20; Zone 5 = -20 to -10 veteran status—as required by Title VI of the Civil Rights Act of 1964, Title IX of the Education Zone 6 = -10 to 0; Zone 7 = 0 to 10 Amendments of 1972, and Section 504 of the Rehabilitation Act of 1973. Oregon State University Extension Service is an Equal Opportunity Employer. Zone 8 = 10 to 20; Zone 9 = 20 to 30