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. A certain amount of impurities (tiny pebbles, bits of stalk, etc.) inevitably find their way into each batch of seeds.

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

Purity: = 85%, Germination: = 75%

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

%Purity x %Germination = %PLS

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 one-pound bag of Bermuda grass actually contains only 64 percent (or less than two-thirds of a pound in our case), of pure, live seed. (It also means that 36 percent or more than one-third of a pound of that one-pound bag is just useless material!)

So, in order to get one 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 one 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...

...this means that you would need 1.56 pounds of bulk seed in order to get one pound of pure live seed (with the percentage purity and germination stated on the bag in this example).

The experts have recommended that you seed Bermuda grass at 1.2 PLS per acre and you have one acre to seed. How much of the bulk seed product do we need? Here’s the formula:

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