Simply stated, Pure Live Seed, or PLS, is the percentage of viable seed in a given lot. It is calculated by multiplying the purity percentage by the total germination percentage.
Every type of seed and every lot of seed has different purity and germination characteristics. For example, chaffy seed (such as most Bluestems) typically has a lower PLS. This is because chaffy seed is more difficult to clean and so the purity is not as high as it would be in smooth, slick seed (such as most Small Grains), which can be easily and thoroughly cleaned. This is the reason that a lot of the grasses, especially native and pasture grasses, are sold by the pure live seed pound and not the bulk pound (physical pounds weighed on a scale). By buying the seed this way, you are buying the amount of viable seed that you need to do the job, regardless of the bulk pounds.
How to Calculate PLS
First, look at the analysis tag attached to bag. Multiply the purity percentage by the germination percentage. For example, 95% purity multiplied by 85% total germination equals a 80.75% PLS. This means that out of every bulk pound of that bag of seed that you plant, 80.75% of it is actually seed of that tagged variety and has the potential to germinate.
If you know how many PLS pounds of seed you need, but want to know how many bulk pounds it will require:
Divide PLS pounds by the PLS percentage of the seed lot.
For example, you need 20 PLS pounds of Little Bluestem. Lot 101A of Little Bluestem has a PLS of 80.75%.
20 ÷ 0.8075 = 24.77
This means you need 24.77 bulk lbs of Lot 101A to get 20 PLS lbs.
If you know how many bulk lbs of seed you have and want to find out how many PLS lbs it contains:
Multiply the bulk lbs by the PLS percentage of that lot.
For example, you have 30 bulk lbs of Little Bluestem Lot 101A, which has a PLS of 80.75%.
30 X 0.8075 = 24.23
This means that in 30 bulk lbs of this lot, you have 24.23 PLS lbs.
If you know the bulk lb price, but want to find the price per PLS lb:
Divide the bulk lb price by the PLS percentage of that lot.
For example, you know the price per bulk lb of Little Bluestem Lot 101A, which has a PLS of 80.75%, is $6.50/bulk lb.
6.50 ÷ 0.8075 = 8.05
This means that each PLS lb of this lot costs $8.05/PLS lb.
If you know the PLS lb price, but want to find the price per bulk lb:
Multiply the PLS lb price by the PLS percentage of that lot.
For example, you know the price per PLS lb of Little Bluestem Lot 101A, which has a PLS of 80.75%, is $9.25/PLS lb.
9.25 X 0.8075 = 7.47
This means that each bulk lb of this lot costs $7.47/bulk lb.