Why aerate in the fall and why overseed?
Aeration can be done almost anytime with the spring and the fall being the best time periods. The main reason fall takes an edge over spring is due to a few important facts. First, the soil is already warm from the summer so seed will germinate much faster compared to the spring. Second, annual weeds like crabgrass or spurge have completed their life cycles and are on the way out (dying) instead of growing larger. The reduced competition is most helpful to young turf plants which don’t have to compete for air, light, moisture, and nutrients in the fall. Most lawns will benefit from additional seeding, whether in existing established turf or thinner lawn areas. Overseeding is not designed to create a lawn in bare areas but add to existing lawn regardless of the condition (great to thin). The primary reason to overseed your lawn after aeration would be to introduce a superior grade grass into the lawn. A perfect overseeding example would be where the kids play or an area that dries out frequently. Adding a drought tolerant turf such as tall fescue is a wonderful tactic to add new grass and upgrade the lawn area while not undertaking a costly renovation. In most situations, working with the existing lawn is a faster and more economical position than starting from scratch. Since turf usually takes a hit in summer heat, being proactive for the next year is critical since the window of opportunity only comes twice a year!
What is thatch?
Thatch is defined as living and non-living “stuff” lying between the upper turf blades and the soil. A thatch layer between 0-1/2” is considered healthy but one approaching 1” or greater resists water absorption like a dry sponge. Excessive thatch also encourages many types of insects and disease issues. Aeration is also useful for reducing compaction in clay or heavily used lawn areas. Aeration may seem simple enough, but it is a very labor intensive process- especially when using our heavy, commercial grade machines. While you may be able to rent a small aerator, a large benefit derived from a larger unit provides deeper hole, especially in compacted soil. If you do decide to rent an aerator- be sure the tine tips are not worn down. Aeration is especially beneficial when followed by over seeding to thicken and add improved grass varieties.
Commercial grade aerators physically remove plugs from your lawn which improves water, moisture, and nutrient absorption into the soil while enhancing root growth and thatch decomposition. Dethatching machines slice the lawn creating large volumes of plant debris and can often cause extensive damage if not used properly. Aeration is recommended on all lawns on a yearly basis while dethatching is only left to the most mature, thick lawns with a thatch near 1” as a renovating process.