"My wife contacted you a few times last year regarding our Z3 lawn problem.

"We reside in Mililani Mauka and had Z3 zoysia grass implanted by a landscaping company about 2 1/2 years ago.

"Recently we're experiencing severe grass problems, which are obviously becoming worse. The problems consist of large dry brown areas where the grass appears to be completely dead, or at least there seems to be very little new growth within the dried brown areas.

"I have heard these brown spots may be due to a thatching problem. Our lawn is a little spongy, and it's clear the thatch does appear to be fairly thick. I recently bought a thatching rake and used it on some of the dead areas. This did not help at all.

"Prior to this problem, we'd received many compliments on our lawn, but it's strange that once we used a new fertilizer, this problem slowly developed. I fertilize about once every two to three months with UAP 25 3 7. Prior to this fertilizer, we used 28-03-01 MU 2FE.

"I use a McLane seven-blade reel mower every two weeks. Cut is about 1 to 1 1/2 inches. Watering is done three times a week."

Ken Ishimine

After viewing the pictures you sent, I can be reasonably sure that your lawn damage is due to excessive thatch buildup, which means that when you mow, you remove all of the green blades and expose the brown stemmy growth (thatch) that lies under the green leafy part of the grass. This is called scalping.

Thatch is a normal part of all turf grass growth and, if kept under half an inch deep, is beneficial. It acts as a natural mulch, keeping the soil moist and cushioning the grass against foot traffic. Problems arise when the thatch thickness builds up to an inch or more. At this point, it can interfere with water and fertilizer penetration into the soil, is more likely to harbor harmful insects and some lawn diseases, and cause scalping.

Actually, the scalping is usually one of the first signs that the thatch is getting too thick. One's first reaction to this is usually simply raising the cutting height on the mower, which will work for a while but eventually leads to an even thicker layer of thatch and greater mowing damage.

So what is the remedy? Thatch buildup is faster in some species of turf than others, but is increased by three maintenance practices: over-fertilization, over-watering and mowing at too high of cut. Too much nitrogen fertilization and too much water both result in a more rapid growth rate and hence thicker thatch. Some turf species require more nitrogen than others.

In your case, Z3 zoysia is a fairly slow-growing species and does not need much fertilization once it is established. You have been applying a high-nitrogen fertilizer once every several months, which is too often for Z3. Twice a year, using a slow-release nitrogen fertilizer, is probably enough. Watering should depend on the season and be more infrequent but for longer duration with each watering. This will allow deeper water penetration into the soil and allow roots to grow deeper.

And finally, the mowing height should remain within the range of heights recommended for your particular species of grass. Tom Staton, who developed Z3 at his sod farm in Waimanalo, recommends that Z3 be mowed at 1/2 to 3/4 inch. Any height below one inch requires the use of a power reel mower, and the blades should be kept sharp and the mower in alignment. Mowing frequency should be determined by how rapidly the grass is growing and following the rule of removing no more than one-third of the grass blades at each mowing.

Once the thatch reaches one inch or more and is a constant problem during mowing, it is time to remove it. The process is called de-thatching and is done with a special type of mower called a verticutter. This will remove much of the brown stemmy material, as well as most, if not all, of the green leafy blades in the lawn, so be ready for a period of time where the lawn looks scalped and brown. However, if done correctly and at the right time of year, the lawn will produce a new lush growth of nice green leaves.

I will cover the entire process of verticutting in my next issue, which will run on April 3, just in time to start your preparation.