Pure Live Seed Calculation

Pure live seed basics

Recommendations for establishing a turfgrass from seed uses the term pure live seed (PLS) within the seeding rate. Although many homeowners are not aware of the PLS term, PLS can really affect turfgrass establishment success. The term PLS is a calculation based on the purity and germination rates found on the seed label. By law, certified seeds must be labeled with the purity and germination as well as other relevant information. Because purity and germination percentages vary between species, cultivars and seed lots, the term PLS helps you adjust seed weight to attain the proper amount of seed needed to achieve establishment. Remember, the term pure live seed really is stating what it is — the percentage of seed by weight within the bag that you want and is expected to germinate.

How to calculate pure live seed

Step 1: Determine the total weight of seed needed to establish a known area based on the recommended PLS seeding rate for the desired turfgrass species.

For example: 20,000 ft² x 1 lb. of PLS ÷1,000 ft. = 20 lbs. PLS

Step 2: Locate the seed purity (%) and germination (%) of the species on the seed label.

For example:

Step 3: Perform the following calculation: PLS = % seed purity x % seed germination

For example: 0.48 x 0.80 = 0.38

Step 4: Divide the solution from Step 1 by the pounds PLS calculated in Step 2.

For example: 20 lbs. PLS ÷ 0.38 = 52.6 lbs. seed

Step 5: The weight of seed calculated in Step 4 is the weight of seed needed to seed the lawn based on the calculation of PLS from seed purity (%) and germination (%).

*Cool-season turfgrasses with seeding rate for overseeding warm-season turfgrasses.

Seed blends vs. seed mixtures

Not all bags of seed contain one turfgrass species or cultivar. A seed blend contains the same turfgrass species but different cultivars of that species, whereas a seed mixture contains different species. Having different cultivar blends or species mixtures can provide the benefits of increased turfgrass stand tolerance to biotic and abiotic stresses.

How to calculate pure live seed for a blend or mixture

Step 1: Determine the total weight of seed needed to establish a known area based on the recommended PLS seeding rate for the desired turfgrass mixture or blend.

For example: 20,000 ft² x 2 lbs. of PLS ÷ 1,000 ft² = 40 lbs. PLS

Step 2: Locate the seed purity (%) and germination (%) for the seed mixture or blend on the seed label.

For example:

Step 3: Perform the following PLS calculation for each species or cultivar and add the calculated PLS with the seed mixture or seed blend.

For example: Pure Live Seed = % seed purity x % seed germination

Centipedegrass: 0.25 x 0.80 = 0.20

Carpetgrass: 0.70 x 0.90 = 0.63

Total seed mixture PLS = 0.83

Centipedegrass Cultivar 1:0.45 x 0.90 = 0.41

Centipedegrass Cultivar 2:0.50 x 0.80 = 0.40

Total seed blend PLS = 0.81

Step 4: Divide the solution from Step 1 by the total PLS calculated in Step 2.

For example:

40 lbs. PLS ÷ 0.83 = 48.2 lbs. seed

40 lbs. PLS ÷ 0.81 = 49.4 lbs. seed

Step 5: The weights of seed calculated in Step 3 are the weight of seed needed to seed the lawn based on the calculation of PLS from seed purity (%) and germination (%) for the seed mixture or seed blend.

Download here: Louisiana Home Lawn Series: Pure Live Seed Calculation 3624-RRR