Calculating the Price of Pure Live Seed

Sometimes, turfgrass seed that is low in purity and germination is sold at a reduced price. The amount of seed required to compensate for poor purity and germination can be determined by calculating percent pure live seed (PLS). Pure live seed indicates the amount of seed in the container that is capable of developing into seedlings.

To calculate PLS, the percentage of pure seed of a cultivar, which should always be listed on the seed label, is multiplied by the percent germination (also listed on the seed label), and the product is divided by 100. For example, 92% pure seed of the cultivar x 80% germination / 100 = 74% PLS. To determine how much seed to plant, divide 100 by the percentage PLS (74% in this case). Thus, in this example, 100/74 = 1.4. Thus, 1.4 pounds of seed with a purity of 92% and a germination of 80% would be needed for each pound specified in the desired seeding recommendation.

One way of determining if seed with low purity and germination is really a good buy is to divide the PLS into 100 then multiply by the cost of the seed. A comparison of two seedlots (A and B) is provided as an example.

'Seedlot A' label states 85% purity and 60% germination

Assume Seedlot A is sold at the reduced price of $1.95 per pound and you want to determine if this is a bargain based on PLS:

PLS = (85% purity) x (60% germination) / 100 = 51%
100 / 51 = 2 pounds of seed needed per pound of seed specified
Cost = $1.95 x 2 = $3.90 per pound of PLS

'Seedlot B' label state 99% purity and 90% germination

Assume Seedlot B is sold at the regular price of $2.50 per pound:

PLS = (99% purity) x (90% germination) / 100 = 89%
100 / 89 = 1.1 pound of seed needed per pound seed specified
Cost = $3.00 x 1.1 = $3.30 per pound of PLS

A comparison of actual cost per pound of pure, viable seed reveals that seed that appeared to be a bargain (Seedlot A) was actually more expensive than Seedlot B.

Prepared by Peter Landschoot, Professor of Turfgrass Science, Penn State