The amount of crimson clover seed (Trifolium incarnatum) required per acre depends on the intended use and the application method. This quick-growing, cool-season annual legume is valued in sustainable agriculture for improving soil health, primarily through nitrogen fixation. Its dense growth habit provides excellent seasonal ground cover and weed suppression.
Primary Uses That Influence Seeding Density
The ultimate goal for the crimson clover stand dictates the necessary seed density. Using the plant as a cover crop or green manure requires the highest seeding rate to maximize biomass production and nitrogen contribution. A dense stand ensures the greatest amount of organic matter is incorporated, with nitrogen fixation potentially ranging from 70 to 150 pounds per acre.
For forage or hay production, a moderate density is preferred to balance high yield with quality, often requiring a slightly higher rate than a cover crop to promote finer stems. Hay yields can reach 1 to 2.5 tons of dry matter per acre. Conversely, planting for erosion control, soil stabilization, or as a wildlife food plot utilizes the lower end of the recommended seeding range. These applications prioritize establishing a sturdy root system and reliable ground cover over maximum foliage density.
Recommended Pure Stand Seeding Rates
The method used to place the seed significantly impacts the required amount of crimson clover seed per acre for a pure stand. Drilling is the most efficient method, placing the seed at a precise depth and spacing, thus requiring less seed. When drilling into a firm, well-prepared seedbed, the recommended rate for pure live seed (PLS) typically falls between 15 and 20 pounds per acre.
Broadcasting the seed involves scattering it over the soil surface, which is less precise and requires a higher rate to compensate for poor soil contact. For this method, the rate generally ranges from 20 to 30 pounds of PLS per acre. If broadcast, a light disking, cultipacking, or dragging is often necessary afterward to improve seed-to-soil contact and ensure adequate establishment. Aerial application may require rates up to 30 pounds per acre due to the lack of mechanical soil incorporation.
Adjusting Rates for Seed Mixtures and Soil Conditions
When crimson clover is planted in a mixture with other species, such as cereal rye, oats, or annual ryegrass, the clover seeding rate must be reduced to avoid excessive competition. Growers commonly reduce the rate to 40% to 60% of the pure stand rate. This places the clover seeding rate in a range of 8 to 12 pounds per acre when drilled with a companion crop. For example, a mixture might use 8 to 12 pounds of crimson clover with 30 to 40 pounds of cereal rye per acre.
Soil quality and local environmental factors necessitate small adjustments to standard rates. In areas with highly fertile, well-drained soils, growers can use the lower end of the recommended range (e.g., 15 pounds per acre drilled) because germination and survival rates are expected to be high. Conversely, if planting into poor, heavily tilled, or rocky soils, or later in the season, the seeding rate should be increased slightly. A 10% to 15% increase above the standard rate ensures sufficient plant population under less-than-ideal conditions.
Critical Factors for Successful Seed Establishment
Beyond the correct seeding rate, planting technique and timing are paramount for successful stand establishment. Crimson clover is typically planted in the late summer or early fall, allowing the plant to establish before the first hard frost. This timing is important for the clover to overwinter reliably and provide maximum growth in the spring. Planting should occur six to eight weeks before the average date of the first killing frost.
Proper planting depth is critical, requiring shallow placement due to the seed’s size. The seed must be planted at a depth of no more than one-quarter to one-half inch. Planting deeper than one-half inch significantly reduces germination success.
Inoculation
Successful nitrogen fixation relies on the presence of the correct symbiotic bacteria. Therefore, the seed should be inoculated with the specific Rhizobium leguminosarum biovar trifolii (“R” type inoculant) immediately before sowing, especially if the field has not grown clover recently.