Pure Live Seed
All wildflower and grass seeding rates are specified in terms of "pounds, pure live seed." The total weight of a seed bag is not the pounds of pure live seed because the contents will not be 100% pure nor will every seed germinate. This is not a reflection of poor business practices by the seed industry, but rather the nature of the seeds which cannot be changed.
Calculating Pounds of Pure Live Seed
To determine the amount of Pure Live Seed (PLS) in a seed bag, use the following formula: %purity x % germination = %PLS.
For example, a 1-pound bag of Bermuda grass seed might contain the following information: purity = 85%, germination = 75%. The PLS formula for this bag of Bermuda grass seed would be: 0.85 x 0.75 = 0.64 PLS.
In other words, the 1-pound bag of Bermuda grass seed actually contains 64% (or 0.64 pounds), of pure, live seed. It also means that 36% or 0.36 pounds is unneeded material.
In order to get one pound of pure live seed, it's best to set up a basic proportion equation which says ".64 pounds pure live seed is to one pound, as one pound is to x pounds pure live seed." The equation would look like this: 0.64:1 = 1:x
Solving the equation you would find, 0.64x = 1 and then, x = 1/.64 = 1.56 (lbs. bulk) Therefore in our example, you would need to purchase 1.56 pounds of bulk seed in order to get 1.0 pound of pure live seed.