Fall planting of cool season grasses such as bluegrass and tall fescue is close at hand, so it’s time to talk about seed.
Overseeding requires many steps to achieve success, but one of the most important is choosing high-quality seed.
Many people think all grass seed is the same. Big mistake! If you don’t know what to look for, you may be introducing unwanted intruders into your lawn. You should be concerned with seed contaminated with orchardgrass and/or rough bluegrass (Latin name, Poa trivialis, or Poa triv for short). Both are perennial grassy weeds that cannot be selectively controlled once they are in a lawn.
Orchardgrass grows faster and is lighter green than our turfgrasses. It is a bunch grass so it doesn’t spread, but infested areas are still unsightly. Rough bluegrass is fine-textured and forms circular patches. It blends in fairly well until summertime heat causes it to rapidly turn brown. If the rough bluegrass would just die in the heat, it would be a temporary problem. Unfortunately, it just goes dormant, turning green again with cooler temperatures and rain.
Buying good-quality seed starts with deciphering the label. 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 turfgrasses other than the one you are buying and pasture grasses. Orchardgrass and rough bluegrass both are listed as “other crop” seed.
Seed labels are required by law to show the percentage (by weight) of “other crop” in the bag. But unless a species constitutes 5 percent or more, the label doesn’t have to list the species.
How much “other crop” is too much? It depends on what the “other crop” actually is and the expectations of the buyer. “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 orchardgrass.
A homeowner has no easy way of knowing what the “other crop” is. If it is something bad, less than one-half of 1 percent can ruin a bag of seed. For example, if a bag of tall fescue seed contained 0.5 percent orchardgrass, the buyer would end up “planting” 12 to 16 orchardgrass 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.
If your quality expectations are high, you want the “other crop” to be as close to zero as possible. Good-quality seed often has 0.01 percent “other crop” or less.
Also, check the label for inexpensive mixes laced with other turf species. Many times bluegrass or tall fescue will have perennial rye in the bag. Rye germinates quickly but dies out under harsh summers.
When it comes to grass seed you get what you pay for. Read the label and always purchase from a reputable garden center. Avoid most bagged seed mixes sold for a regional or national market. They don’t withstand our Kansas City climate.
Dennis Patton is a horticulture agent with Kansas State University Research and Extension. Got a question for him or other university extension experts? Email them to firstname.lastname@example.org or visit KCGardens