The Purdue Plant and Pest Diagnostic Laboratory

P&PDL Picture of the Week for
March 21, 2005

Late Winter or Very Early Spring Overseeding to Reduce Summer Weed Problems

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

Promoting a thick, healthy stand of turfgrass is the best form of weed control.  While proper fall fertility provides the first step toward reconditioning a lawn after a tough summer, fall overseeding may also be necessary when baseball to softball size holes are present.  Fall has passed, but there may still be time to overseed with some benefit.

Grass seed can be particular when it comes to planting for good germination.  If it’s buried too deeply or if it’s laying loosely on the soil surface germination will be spotty and thin.  Grass seed must be in solid contact with the soil to reduce the chance of the drying out too easily.  To accomplish good seed to soil contact a power rake or slicer can be utilized to create shallow grooves in the soil (<1/4”).  Seeds that fall into these grooves have a much better opportunity to germinate.  Another method to achieve good seed to soil contact is to spread seed before or during freeze/thaw cycles.  During a freeze period, the soil surface tends to “honeycomb” opening the surface slightly.  As the soil thaws, the open spaces tend to close.  This action works the seed into the soil surface enough to accomplish good seed to soil contact.

As we approach spring, it is best to overseed as early as possible in order to give the seedlings as much time as possible to mature before they must endure the heat of summer.  If you choose to overseed during the winter or early spring, avoid applying preemergent crabgrass control, since it will prevent germination of your grass seed as well as the crabgrass seed.  For more information check AY-13: Lawn Improvement Programs.

Click on image to enlarge

Soil surface during a 40 degree F day.

Soil surface the next morning after a night in the 20’s.

Power rake/slicer for rent.

Blades (not springs) for cutting grooves.

Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service