Orchardgrass and/or rough bluegrass (Poa trivalis) are the names to watch for when preparing to overseed. These perennial grassy weeds cannot be selectively controlled once introduced to a lawn.
Orchardgrass grows more rapidly and is lighter green than our turfgrasses. It doesn’t spread but creates unsightly tufts of light green bunch grass in the lawn. Rough bluegrass creates fine-textured, circles in the lawn. Initially it can blend in with the other grasses, but turns brown quickly with the summer heat. When temperatures cool it greens up again.
Understanding the contents printed on the label of the grass seed bag will save you from introducing unwanted species. Look for the percent “Other Crop Seed” or “Other Crop” printed on the label. “Other Crop” includes any species grown intentionally such as turfgrasses and pasture grasses. Unfortunately, orchardgrass and rough bluegrass fall into this category. By law, seed labels must identify the percentage, by weight, of “Other Crop Seed” in the bag. However, the species does not have to be named unless it constitutes 5% or more of the contents.
Knowing what percentage of “Other Crop” is too much depends on what the “Other Crop” is comprised of as well as the buyer’s preference. “Other Crop” could include small amounts of a species that will not significantly impact your lawn such as perennial ryegrass in a bag of tall fescue. On the other hand, it could include orchardgrass or rough bluegrass. Since the homeowner has no easy way of knowing what is included in the “Other Crop,” look for a bag of seed where the percentage of “Other Crop” is as close to zero as possible. Quality seed may have 0.01% “Other Crop” or less. “Weed Seed” listed on the label should also be 0.01% or less. (Cynthia Domenghini)