By all indications, this has been one of the worst summers I have experienced since arriving in Lawrence four years ago. The excessive heat, combined with drought conditions, has turned beautiful lawns and landscapes into sun-baked patches of dried plant material.
With fall coming up, weather patterns should change, and cooler temperatures will bring some much-needed rain. Soon it will be time to overseed our cool-season lawns.
Here is why fall is such a good time to perform this annual practice:
The cool season grasses (fescue, bluegrass and ryegrass) have two primary growth periods. They correspond with the cooler times of the year -- spring and fall. After enduring a long hot summer, these grasses will soon be emerging from summer dormancy and will resume healthy strong growth. However, some plants may not wake up. The stresses of summer were more than they could handle. So as we enter the fall growth cycle, it is time start planting again.
Why not just leave the bare spots? Two reasons. First, cool-season grasses do not "fill in" as quickly as warm-season grasses. They reproduce by stolens and rhizomes but not to the degree of zoysia grass or Bermuda grass. In order to fill in the empty spots, a seed must be planted.
Secondly, achieving a complete cover is the first step in your weed control program. Weeds are adventitious. They take advantage of light, water and space. Look around your own home lawns. The majority of weeds start growing in a bare spot where there is no competition. If you overseed on a regular basis and fill in those bare spots, weeds will naturally disappear.
Is fall really better than spring? Yes. There are several reasons fall is the ideal time to overseed. First, the cool nights and warm soil help the seeds get a quick start. The roots grow fast and the plant matures much more quickly than in the spring. Secondly, the hot, dry summer that follows the spring can kill many new plants that have not had a chance to harden off. Conversely, the fall-planted seeds mature more quickly and are better able to handle the winter season. Finally, the primary weeds that cause the most problems such as crabgrass, foxtail and nutgrass germinate in the spring -- the same time a spring planted lawn is trying to start. Often times, these weeds will out-compete for the light, water and space resulting in a weedy thin stand of turf. Counter that with a fall seeding when these weeds are not growing, and the result is a lush, healthy stand of grass much more quickly.
Finally, fall overseeding can combine several good practices into one major event. Planting seeds, core aeration and fertilizing can all be done at the same time. I am a big proponent of all three. First, overseeding helps rejuvenate an otherwise sickly lawn. Core aeration helps alleviate heavy compacted soil, reduce thatch, and allow water, oxygen, and nutrients to enter more deeply into the soil. And fertilizing gives the grass that fall jump-start.