Grass feeling spongy? Dethatch in late spring, but do it with care

Q: I have been told I need to dethatch my lawn. Should I do it this month or wait until later? From Rod


Answer: With all the cold weather we've had this winter, it would be best to wait until after the turf greens up and is actively growing, but before the hot, potentially dry weather of July and August. May through early June is ideal.

If this spring is dry, be sure to keep the root zone moist during spring green-up. Apply at least 1/4-inch per week until 50 percent green-up, then go up to 1/2 to 1 inch per week, depending on your soil type.

Watering during this time can literally save your grass. But we may get enough rain so you don't have to water. Having adequate water during green-up can get your grass off to a good start for the rest of the season.

I mention watering because all management practices play a role in having a healthy lawn.

Dethatching can be important for any lawn. Thatch is a buildup of dead grass stems and other plant matter between the grass and the soil. If thatch gets more than 1/2-inch thick, you need to do something about it. When it gets too thick, the root system of the grass starts growing in the thatch, not in the soil.

This can lead to problems for the lawn. Thatch freezes faster than soil, which can make winterkill worse when hard freezes come. Thatch dries out faster than soil too, so the lawn will be stressed more by summer drought. Thatch is also a good environment for insects and disease organisms that can injure the grass.

You didn't say what kind of grass you have, but you may have a thatch problem, particularly if you have centipede. Is your lawn really spongy and soft when you walk on it? Dig your fingers into the sod, grip the grass, and try to move it around. If the grass moves, you have too much thatch. It shouldn't move at all.

How do you get rid of thatch? Most people use a vertical mower (from an equipment rental place) or some attachment to a lawn mower.

On centipede or St. Augustine, the vertical mower blades need to be two to three inches apart. Blades closer than that would remove too much turf and increase recovery time for the grass, and you should go across the lawn only one time.

With Bermuda and zoysia grass, the blades can be closer together and you can go across the lawn more than once.

Don't try to get rid of all the thatch at once. Do it gradually to prevent too much damage.

You can certainly manually get thatch out of your lawn by raking it. But this can be backbreaking work, especially if you have a large lawn. For a small lawn and someone in good shape -- no problem.

Probably a better way to dethatch, especially if you have centipede or St. Augustine (since vertical mowing tears it up so bad) is to topdress the lawn. Topdress with 1/4-inch of weed-free soil, similar in texture to the existing soil. Topsoil contains millions of microorganisms that will aid in the decay of thatch. Don't use pure sand as it does not contain the microorganisms of soil.

Don't fall for some of these "miracle liquids" that you may run across, particularly on the Internet, that say they will break down thatch in a lawn. One tablespoon of soil will typically contain more microorganisms than the whole 2.5 gallon product.

If you see people burning their lawns during the winter, that is what they are doing -- getting rid of the thatch. I usually don't recommend this for several reasons.

In some counties, such as Richmond and Columbia, and in most subdivisions, there are outdoor burning ordinances. Another reason is it can be dangerous if the fire gets away from you. Some grasses can take burning better than others. Bermuda and zoysia can be burned more successfully than centipede and St. Augustine because the first two go fully dormant. I've seen people burn centipede successfully, but if you have some green plant material and the fire gets too hot, you risk killing some of it. So, for most people, burning is not a good idea.

The best way to handle a thatch problem is to prevent it. You can do that by mowing your grass at the proper height. Mow often enough so that you remove only a third of the total height. You also get a bonus if you mow the grass on a good schedule. Besides keeping thatch from building up, you don't have to remove the grass clippings, and that allows you to recycle your costly fertilizer all summer.