P&PDL Picture of the Week for
January 7, 2008

New Lawns with Clumpy Perennial Ryegrass

Glenn Hardebeck, Turfgrass Research Agronomist, Department of Agronomy, Purdue University

New Lawns are often seeded with a mix of perennial ryegrass, Kentucky bluegrass and fine fescues.  Perennial ryegrass is included for its quick cover, Kentucky bluegrass for its recuperative ability and fine fescues for shade tolerance.  Unfortunately, in many cases the perennial ryegrass does its part too well.  It germinates very quickly and as a strong seedling, it dominates the turfgrass stand.  Since perennial ryegrass is very disease susceptible and is a bunch-type grass with little ability to spread into voids, thin, clumpy lawns can often result.

If you noticed severely thinned turf areas in your lawn before the recent snowfall, dormant overseeding with a blend of Kentucky bluegrass cultivars would be an easy choice to improve the situation.  Dormant overseeding can be accomplished anytime from December through early March.  Mother Nature will “plant” the seed for you through natural freeze-thaw cycles and it will germinate when the soil warms next spring.  A limitation is that dormant seeded turf cannot be treated with a crabgrass pre-emergent herbicide next spring.  Instead, a post-emergent product such as Drive should be used to treat crabgrass after it germinates.

A final note would be to avoid the situation, if possible, by limiting the perennial ryegrass component of a seed mix to 10-15%.  More information can be found at

Click image to enlarge

clumpy ryegrass

A severely thinned stand of perennial ryegrass will not spread and fill in without overseeding.

Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service