According to Iowa State University, you should stop mowing your lawn in the fall only when it stops growing and goes into dormancy. In areas where cool-season grasses are planted (where summers are short and warm, and winters are cold) your lawn stops growing when daytime temperatures are regularly below 50 F, usually sometime in late October or November. In warmer areas of the country, dormancy may not occur until January.
The height of your cut matters a great deal, especially when going into winter. You should only mow when it’s reached 4-4.5″ high so it can be mown to 3″. This is standard protocol during the growing season and should continue through the fall to the last cut. Three inches of height allows the blades of grass to maximize photosynthesis and establish strong, deep, healthy roots to choke out weeds and manage water. Cutting the lawn shorter causes the grass to use up nutrients faster as it funnels its energy into top growth to regain that height as quickly as possible. While everything appears normal to the homeowner, the grass is actually using all of that energy for top growth and uses less for root growth which is necessary for strong, drought-resistant plants. A three-inch height also helps the grass to remain upright and is the perfect height to shade the soil from the hot summer sun and suppress weed growth. Naturally, as days become shorter, your grass will grow slower, so your weekly routine might move to every 10 days or even 14 in the fall. Maybe even to 3 weeks by the time you do your final cut as winter looms.
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Early fall is also the perfect season for other lawn care:
- Aerate your lawn. Aeration is removing plugs of soil from the turf, creating pores that carry water and nutrients to the grass roots and through the soil.
- Remove thatch if the layer is deeper than 1/2″. Thatch is the buildup of old grass roots and rhizomes below the green vegetation but above the soil line.
- Reseed bare spots in the lawn. The warmer soil temps from mid-September to early October help the seed germinate faster than in spring. There is also less competition from weeds.).
- And rake up leaves to prevent them from matting on the lawn and blocking light and water which impedes growth.
Send your lawn into the winter as healthy as possible to avoid winter damage from snow, ice, frost, diseases, and rodents!