The amount of turnip seed (Brassica rapa) needed per acre varies significantly because this fast-growing crop is utilized for two distinct purposes: producing large edible roots or generating substantial leafy forage and cover crop biomass. Turnips are a cool-season brassica that establishes quickly, and the density of the final stand determines the crop’s output. The seeding rate is a variable range directly tied to the grower’s intended use and chosen planting technique.
Understanding Seeding Goals
The primary objective dictates how densely the seeds should be sown, creating a trade-off between root size and foliage quantity. For maximum root development, the goal is to provide individual plants with ample space, minimizing competition for light, water, and nutrients. Crowded plants focus energy on upward growth, resulting in large tops but small, underdeveloped roots.
Conversely, maximizing greens or forage production requires a much higher seeding rate to achieve a dense stand of leafy material. High-density planting forces turnips to prioritize the rapid growth of tender leaves over the slow expansion of the root bulb. This method is common when planting for livestock grazing or for harvesting the tops as a leafy green vegetable.
The highest seeding rates are reserved for cover cropping or green manure applications. The goal is to establish a dense canopy quickly to suppress weeds, prevent soil erosion, and scavenge excess soil nutrients. A dense stand ensures maximum biomass production and soil coverage, often with the roots acting as natural soil-loosening agents.
Recommended Seeding Quantities
The standard seeding rate is expressed in pounds of Pure Live Seed (PLS) per acre, depending on the desired outcome. Growers aiming for large, mature root development should use the lowest rate, ranging from 1 to 3 pounds per acre. This sparse planting allows for adequate spacing, often requiring subsequent thinning to ensure each plant forms a substantial bulb.
For those focused on producing a high volume of greens or forage for grazing, the recommended seeding rate increases significantly, falling between 2 and 6 pounds per acre. This higher density promotes vigorous leaf growth and is favored when planting forage varieties bred for prolific tops. This rate is also appropriate for planting in mixtures with other cover crops, ensuring sufficient biomass contribution.
When the objective is maximum soil coverage for weed suppression or green manure, the seeding rate should be at the upper end of the spectrum, sometimes reaching 4 to 7 pounds per acre when drilled. Seed size and germination viability can vary between lots. Therefore, a rate based on the number of seeds per pound—around 192,000 seeds for a typical turnip pound—provides a more precise calculation.
How Planting Method Changes the Rate
The method used to distribute the seed directly influences the amount required to achieve the desired plant density. Drilling, which involves planting seeds in precise rows at a consistent depth, is the most efficient method. Because drilling ensures optimal seed-to-soil contact and uniform placement, it allows for the use of the lower end of the recommended seeding ranges.
Broadcasting, which involves scattering the seed over the soil surface, is inherently less precise, resulting in uneven distribution and inconsistent planting depth. To compensate for this variability and the loss of viable seeds due to poor soil contact or predation, the seeding rate must be increased. When broadcasting, growers should use the higher end of the recommended ranges, often increasing the rate by 25% to 50% compared to drilling. For example, a cover crop rate of 3 pounds per acre when drilled may need to be increased to 4 or 5 pounds per acre when broadcast.
Necessary Soil Conditions and Timing
Achieving a successful stand relies on providing the correct environmental conditions for germination and early growth. Turnips are a cool-season crop that can be planted for a spring harvest, two to four weeks before the last expected frost, or for a common fall harvest from late summer through early fall. The optimal soil temperature for rapid germination is between 60°F and 70°F, though seeds can sprout in soil as cool as 40°F.
Turnips thrive in well-drained, loose soil, such as a sandy loam, with a soil pH that is slightly acidic to neutral, ideally ranging from 5.5 to 6.8. The small seeds require very shallow planting, with an ideal depth of only 1/4 to 1/2 inch. After planting, firming the soil with a cultipacker or roller is necessary. Good seed-to-soil contact draws moisture to the seed and maximizes the emergence rate.