Buying turfgrass seed is not as simple as going to the store and buying the highest- or lowest-priced-per-pound grass seed on the shelf. It takes some knowledge and research to select turfgrass species and varieties that are adapted to your site and that will perform well under their intended use and time of planting. 

A mixture of seed is 2 or more species -- like ryegrass and bluegrass. A blend is 2 or more of same species -- like 3 ryegrasses.

Not all cultivars of lawngrass can be planted from seed. Those that cannot must be vegetatively established with sod, plugs or sprigs.

After identifying varieties that will work for you, find a source of high-quality seed. The seed should be free of other seeds that can cause weed problems later.

Such seed should have a low amount of other crop seed (less than 0.5 percent) and weed seed (less than 0.3 percent). In addition, it should include a low amount (less than 4 percent) of inert ingredients, such as straw, chaff and sand, and it should have a high germination rate (around 85 percent for most species). This would make it a high-quality seed of that cultivar.

That being said, if the seed is coated with fungicides and fertilizer, etc., it will have a high amount of inert ingredients listed due to the weight of this coating. That would be okay, since you may benefit from this premium treatment, but now you must allow for the weight of the coating in seeding rates. The product should state if it is coated.

What you actually wish to pay for and plant is the living, true-type seed in the bag and not all the extra contaminants and dead seed. This living seed of the cultivar is what we call 'pure live seed' or PLS. Unfortunately, you won't be able to find the pure live seed listed on any seed label, so you have to calculate it.

The seed label does include all the information you need to determine pure live seed. Look for "purity" and "germination" on the label. Both are given as percentages. To calculate pure live seed percentage, use the following formula: multiply the purity percentage number by the germination percentage number and divide that result by 100 to get the percentage of pure live seed.

Your next step is to calculate the best buy. When purchasing seed, you need to base price comparisons on the cost of pure live seed and not just the cost per pound of seed.

To determine the cost, first calculate the pure live seed for each seed lot, and then calculate the cost per pound of pure live seed by dividing the price by the PLS expressed as a decimal. The lowest-priced seed is not always the best buy. You should consider both quality and price in cost comparisons.

For example, a seed tag showing values of 85% germination and 95% of the cultivar has a PLS of 85 x 95 ÷ 100 = 80.75 or 81% PLS. Thus about 81% of the weight of this bag will give you live seed of that cultivar.

When planting grass seed, rates to use should be given as pounds PLS per 1,000 sq. ft. or per acre to allow for various types of seed quality.