Between the green, growing blades of grass and the soil underneath your lawn is a spongy layer of surface roots and decaying plant matter called thatch. Thatch is healthy and normal – provided it doesn’t get too thick. Thicknesses of a half-inch or less are fine. Much more than that, and lawns can’t absorb rain and fertilizer as well, leading to faster brownouts in dry weather, less oxygen reaching grassroots, and in severe cases, grass death.
To check for thickness, dig up a square-foot section of turf, and look at it from the side to gauge the layer between the blades and the soil. If the thatch is a half-inch or less, no need to do anything.
What causes a too-thick layer?
Some grass types are naturally more prone to thatch problems than others. Ones that spread by runners – particularly cool-season grasses, Kentucky bluegrass is most likely to build thatch in the winter, as are the warm-season grasses such as buffalo grass and Bermuda grass.
Contrary to a popular belief, letting grass clips on the lawn is not the cause of thatch buildup. In a healthy lawn, clips break down quickly and actually benefit lawns by returning nutrients to the soil. The two main contributors to excess thatch are improper watering (specifically, watering often and shallow) and over-applying quick-release nitrogen.
Frequent, shallow watering encourages surface roots, which can build up and die faster than nature decomposes them. Excess nitrogen causes excessive lawn growth, which also can create more dying matter than nature’s microbes can handle.
How to head off too much thatch
Good lawn care goes a long way in preventing thatch buildups in the first place. If you’re going to water the lawn, do it deeply and less frequently – in most cases, one inch of water once a week or a half-inch of water twice a week. Switching to a fertilizer high in slow-release nitrogen, such as GreenView Fairway Formula Fertilizer, which includes 63% slow-release nitrogen, properly feeding your lawn for up to 12 weeks.
Aerating the lawn every year or two also aids in thatch decomposition, and minimizing lawn insecticides and fungicides encourages healthy growth of the soil microbes that break down thatch.
Beyond that, monitor for thatch regularly, and address it before it builds up to the point of causing lawn damage or becoming a major removal effort.
How to get rid of excess thatch
What to do if your thatch is already too thick? For small areas or marginal problems, thatching rakes (“convex” rakes) can be used to tear out thatch by hand. Even a stiff garden rake can handle small jobs.
For large areas and/or thick thatch, you’ll need power equipment. These range from dethatcher tines that can be attached to lawnmowers up to walk-behind dethatching machines, verticutters, and power rakes that can be rented. Tractor-pulled dethatchers with spikes also are available for the biggest jobs.
Spring and late summer to early fall are the two best times for dethatching. It works best when the lawn is softened (but not soggy wet) after a rain or irrigation and after the grass has been cut short. Locate and avoid any shallow lines and sprinkler heads before dethatching. Rake off and compost removed thatch, then watch to see if the lawn recovers. Give the recovery a boost or patch bare spots afterward by adding fresh grass seed.