Almost all grass seed sold in retail outlets in this country is packaged as a “mixture” or “blend” of seeds of several kinds of grasses. Quality sod is also grown from several kinds of grasses. This is because a diversity of grasses insures a broad representation of genetic strengths to keep lawns healthy and vigorous. Each grass seed package lists the kinds and percentages of the several grass types it contains. They are combined in different proportions depending on whether the seed is to be used in sunny areas or in areas that have some shade during the day. The package will say “shade mixture”, “shade blend” or “sun mixture”.
A “mixture” contains more than one type of grass--perhaps bluegrass and perennial rye. The package label indicates the percentage by weight of each type of grass represented in the mixture. A Kentucky bluegrass mixture is one where bluegrass seed predominates and there are small percentages of perennial rye or fescues of some kind.
A “blend” contains only one type of grass, such as bluegrass. However, the blend contains a number of varieties of bluegrass such as, ‘Baron’, ‘Nassau’, and ‘Abbey’. Each different variety has certain desirable traits and, collectively, they improve the quality of the lawn. However, if you use a blend, all of the grass in the lawn is of the same plant species.
Choosing Mixture Over Blend
On the theory that the more genetic diversity in a lawn, the more vigorous and self-reliant it is, using the highest quality mixture available is usually the best bet. Mixtures provide a more balanced combination of plants, each having unique strengths that offset the vulnerabilities of the others.
While a premium grass seed blend has more uniform texture, since all the plants are the same type, they lack the broad genetic diversity that is a hedge against disease. It is perfectly fine for situations where the "look" of the turf is critically important. In either case, the ultimate success of the seed is dependent on the quality of the soil it is growing in, so add organic matter and aerate the soil to maximize the excellent qualities of the top grade seed.