by Richard C. Snell

Barton County Extension Agent, Agriculture

Kansas

Fall planting time is close at hand for cool-season lawns (not bermuda, buffalo or zoysia), so it's time to talk about grass seed. For seeding success, pay attention to "Other Crop" on the seed label. Many people have the idea that all grass seed is basically the same. Big mistake! Choosing quality seed is one of the most important steps in successfully planting or over-seeding your lawn. If you don't know what to look for, you may be introducing unwanted intruders into that new stand. In particular, we are seeing more and more seed contaminated with orchard grass and/or rough bluegrass (also known by its Latin name, Poa trivialis, or Poa triv for short). These are both perennial grassy weeds that cannot be selectively controlled once they are in a lawn. Orchard grass is a problem because of its coarse texture and rapid growth rate. It grows up above the rest of the lawn and is unsightly. Rough bluegrass is fine- textured and forms circular patches in the lawn. It blends in fairly well until summertime heat when it rapidly turns brown. If the rough bluegrass would just die in the heat, it would only be a temporary problem. Unfortunately, it usually just goes dormant, turning green again with cooler temperatures and rain.

Buying quality seed starts with knowing how to decipher the seed label, and one of the most important things to look for is listed as "% other crop". "Other crop" refers to any species that is intentionally grown for some purpose. That would include turf grasses (those species other than the one you are buying) and forage grasses, which are both perennial grasses that usually cannot be selectively controlled in a lawn.

Orchard grass and rough bluegrass both fall into this category. Seed labels are required by law to show the percentage (by weight) of "other crop" in the bag, however, unless a species constitutes 5 percent or more, the label doesn't have to list each species by name.

How much "other crop" is too much? That is a difficult question to answer, but the tolerance is very low. It depends on what the "other crop" actually is, and what the quality expectations of the buyer are. In practice, "other crop" may refer to something relatively harmless, like a small amount of perennial ryegrass in a bag of tall fescue, or it may refer to something bad, like rough bluegrass or orchard grass.

The homeowner really has no easy way of knowing what the "other crop" is, although there are some tip-offs (tune in next week). If it is something bad, less than 1/2 of 1 percent can ruin a bag of seed. For example, if a bag of tall fescue seed contained 0.5 percent orchard grass, the buyer would end up "planting" 12 to 16 orchard grass seeds per square foot. Similarly, planting Kentucky bluegrass seed containing 0.5 percent rough bluegrass would result in about 25 to 35 rough bluegrass seeds per square foot of lawn Obviously, if your expectations are high for the area you are planting, you would want the "other crop" to be as close to zero as possible (it is nearly impossible for a homeowner to find seed with zero "other crop").