· Michael Blair
Compaction is the normal condition of a Middle Tennessee clay lawn after a few years of use, and it limits root depth, water infiltration and air exchange.
Core aeration
Pulling plugs of soil out and leaving them on the surface. That relieves compaction, opens channels for water and air, and gives autumn overseeding an ideal seedbed.
Spike aeration, which pushes holes rather than removing soil, compacts the walls of the hole and achieves considerably less.
Timing
Autumn for fescue, immediately before overseeding so seed falls into the holes. Late spring to early summer for bermuda and zoysia, during active growth.
Never immediately after a pre-emergent, since it breaks the chemical barrier.
- Core aeration, not spikes
- Autumn for fescue, immediately before overseeding
- Leave the plugs to break down
- Not after a spring pre-emergent application
- Thatch over half an inch needs addressing
What thatch actually is
A layer of undecomposed stems and roots between the soil and the green growth. It is not grass clippings, which break down quickly and do not contribute.
A thin layer is beneficial. Over about half an inch it holds water at the surface, harbours disease and stops water reaching the roots.
Where thatch comes from
Over-fertilising, shallow frequent watering and compacted soil that suppresses the microbial activity that would break it down. Bermuda and zoysia produce more than fescue.
Core aeration helps by bringing soil into the thatch layer and reintroducing the organisms that decompose it.