All wildflower and grass seeding rates are specified in terms of "pounds, pure live seed." The total weight of the seed bag is not the pounds of pure live seed. This is not a reflection of poor business practices by the seed industry, but more a "nature of the beast" which can’t be changed.

Assume that you went to the store and bought a 1-pound bag of Bermuda grass seed. After getting home, you carefully read the seed tag and discover the following information:

Purity: = 85%, Germination: = 75%

To figure the amount of Pure Live Seed (PLS) you have, you use the following formula: 

%Purity x %Germination = %PLS

OK, using that formula with our bag of Bermuda grass, let’s see what we’ve got: 

0.85 x 0.75 = 0.64 PLS

That means that your 1-pound bag of Bermuda grass actually contains only 64% (or 0.64 pounds in our case), of pure, live seed. (It also means that 36% or 0.36 pounds of that 1-pound bag is just useless material!)

So, in order to get 1 pound of pure live seed, you need to set up your basic proportion equation which says ".64 pounds pure live seed is to one pound, as 1 pound is to x pounds pure-live- seed." Or in standard math notation…

0.64:1 = 1:x

Solving for "x," you get…

0.64x = 1

…then finally…

x = 1/.64 = 1.56(LbsBulk)

…which means that you would need 1.56 pounds of bulk seed in order to get 1.0 pound of pure live seed (with this percentage purity and germination).

Now, you say that the experts have recommended that you need to seed Bermuda grass at 1.2 PLS per acre and you have, magically, one acre to seed. How much of this stuff do we need?

1.56(LbsBulk) x 1.2(LbsPLS/AC) = 1.88  …bulk pounds needed.