Establishing a productive alfalfa stand begins with a fundamental question: how much alfalfa seed per acre should you plant? This calculation is not a one-size-fits-all number, but rather a precise target determined by a blend of seed genetics, field preparation, and environmental goals. Getting this rate correct is the difference between a sparse, weedy field and a dense, high-yielding forage crop that pays dividends for years.
Understanding Pure Live Seed (PLS)
Before calculating the pounds per acre, you must understand the concept of Pure Live Seed (PLS). Alfalfa seed bags rarely contain 100% viable seed; they include inert matter and seeds that are dormant or dead. PLS is a standardized percentage that represents the portion of the bag that is both pure alfalfa and capable of germinating. Ignoring the PLS tag is the most common mistake in seeding calculations, as planting based on total weight alone will result in a thin, unreliable stand.
The Role of Seed Size and Technology
The size and coating of the seed dictate the physical rate per pound. Historically, alfalfa was a large, "medium" seed, but modern breeding has produced smaller, denser varieties that allow for lower seeding rates without sacrificing stand density. Furthermore, the advent of seed treatments and polymer coatings has increased the weight of each seed unit. Consequently, a modern coated seed bag will require a different pounds-per-acre calculation than a small, untreated seed of the same variety. Always check the seed tag for the stated seed size, as this directly impacts the poundage needed to achieve your target plant population.
Calculating the Seeding Rate
To determine how much alfalfa seed per acre, you start with your target plant population. For new seedings intended for hay, aim for approximately 15 to 20 plants per square foot in the first year. This high initial density allows the plants to compete against weeds and ensures a robust stand before winter. Using this target, you reverse-engineer the rate by dividing your desired plants per square foot by the germination percentage provided on the seed tag. The resulting number is the amount of PLS needed. To find the actual pounds to purchase, you divide the PLS requirement by the PLS percentage listed on the same tag.
Typical Rate Ranges
While the math is specific to the seed you purchase, general guidelines provide a practical framework. Most standard, uncoated alfalfa varieties recommend seeding between 12 to 15 pounds of PLS per acre. However, if you are using newer, smaller-seeded varieties or planting into less-than-ideal conditions, you might successfully use as little as 8 to 10 pounds of PLS per acre. Conversely, larger seeds or specific disease-resistant varieties sometimes require a higher rate, ranging from 15 to 20 pounds of PLS to ensure optimal coverage.
Adjusting for Environmental Conditions
The "how much" question changes based on the "where" and "when." If you are planting into a clean, cultivated seedbed with high moisture, you can rely on the lower end of the seeding rate spectrum. The seeds will establish quickly and uniformly. Conversely, if you are drilling into existing vegetation, planting on a steep slope, or facing dry conditions, you should increase the rate by 10% to 20%. The additional seed compensates for slower germination, higher competition, and potential early-season loss, ensuring the field reaches the critical density required for winter survival.
