PLS & Seeding Rates
Native seed is sold and specified by Pure Live Seed (PLS), because bulk weight on its own says little about how much viable seed you’re actually getting. We sell all of our seed by PLS, and every label shows both the PLS weight and the bulk weight in the bag.
Skip the mathOur Project Builder works out the PLS pounds for any of our mixes from your area in square feet or acres, rounded up to the whole pound.
What PLS means
A bulk seed lot is never entirely pure, viable seed. Alongside the seed of the labeled species, it contains chaff, stems and other inert matter, as well as some weed seed, other crop seed and seed that won’t grow. Native lots vary widely in this respect, especially for fluffy or hand-harvested species. PLS is simply the share of the bulk weight that is pure, viable seed of the species on the label.
The formulaPLS % = Purity % × Total viability % ÷ 100
Purity and viability both come from a seed test. For native species, total viability usually means germination plus dormant (or hard) seed: seed that is alive but didn’t sprout during the test because it still needed a dormancy treatment. A lot that tests 80% pure, with 50% germination and 25% dormant seed, has 75% total viability. That makes it 80 × 75 ÷ 100, or 60% PLS, so each bulk pound contains 0.6 PLS lb.
Reading our labels
Because we sell by PLS, the bulk weight in the bag will be higher than the PLS weight you ordered; it’s whatever weight of that particular lot it takes to deliver your PLS. We retest our seed lots every nine months so the figures on the label stay accurate.
Use the PLS weight to check the order against your specification, and the bulk weight to calibrate your equipment and plan your passes. A seeder, drill or hydroseeder meters what’s actually in the hopper or tank, not PLS.
Converting between PLS and bulk
The formulaBulk pounds = PLS pounds ÷ (PLS % ÷ 100)
Say a specification calls for 4 PLS lb per acre of a species, and the lot you have is 40% PLS. You’d need 4 ÷ 0.40, or 10 bulk pounds, for every acre.
Seeding rates
Seeding rates are written either as PLS pounds per acre or as PLS seeds per square foot. Seeds per square foot is the better way to compare species, because seed size varies enormously, from tens of thousands of seeds per pound for large-seeded species to well over a million for the smallest. You can convert from one to the other with the number of seeds per pound:
The formulaPLS seeds per sq ft = PLS lb per acre × seeds per lb ÷ 43,560
Use the rate in your project specification, or our recommended rate for the mix, which is shown on each mix page. More seed isn’t always better: too high a rate crowds the seedlings and reduces diversity, while too low a rate leaves bare ground for weeds to fill. On erosion-prone sites, pair the native rate with a nurse crop rather than relying on native seed alone for quick cover.
Scaling rates to your site
An acre is 43,560 square feet. To turn a per-acre rate into a rate per 1,000 square feet, divide it by 43.56; to go the other way, multiply by 43.56.
Store seed wellViability declines as seed ages, which is why every test result on the label carries a test date. Until you sow, keep seed cool and dry; the germination guide explains how.