With the onset of summer our warm-season grasses are again growing at full speed. Mowing, irrigation, fertilization and other lawn-care chores should start to become part of the weekend routine. Some potential lawn problems can be avoided by taking a close look at the condition of your lawn now.

Check for excessive thatch buildup. Thatch is the brown stemmy layer between the soil surface and the green leafy part of the grass. When thatch is more than 1 inch thick, it can cause scalping during mowing, interfere with water and fertilizer penetration into the soil, and provide a hiding place for harmful lawn insects. May and June are the best months to remove thatch. This is done with a type of mower called a verticutter.

Is your soil hard and compacted? Core aeration can improve that situation. For best results, verticut the lawn, water deeply then core aerate and topdress the lawn with a thin layer of compost the next day. Apply 3 or 4 pounds of a lawn fertilizer for every 1,000 square feet of treated area and keep moist until the grass grows back in. (See the July 29 and Aug. 5, 2006, Hawai'i's Gardens columns for more details). Verticutters and core aerators are available at most equipment rental shops.

A few other summer lawn care hints:

Regular mowing at the proper mowing height and with the right equipment is a must for maintaining a healthy lawn. Proper mowing promotes better rooting, higher surface density and uniform grass growth. A thin, weak turf can be converted into a thicker, more wear-resistant surface if mowed at the correct height and frequency. Mowing frequency is based on the general rule of removing no more than one third of the leaf blade at each mowing. It is important to stay within the recommended lowest and highest mowing height for the type of grass you have. Mowing lower than the recommended height leads to a weak turf. Mowing too high or not often enough results in scalping, thin puffy growth and slower recovery from wear.

Use a rotary type mower for mowing heights above 1 inch and a reel type mower for cuts below 1 inch. Reel mowers produce the finest cut but are much less maneuverable and more expensive to purchase and operate. With regular mowing, clippings should be left on the lawn to recycle nutrients.

Proper fertilizer rates and timing are also important for good turf color, appearance, health and wear resistance.

A good routine maintenance turf fertilizer should have an NPK ratio (the three numbers on the front of the bag) of 3 to 4 parts nitrogen: 1 part phosphorus and 2 parts potassium. An average actual analysis will be something like 30:7:15. Many of the garden shops carry fertilizers with a higher ration of N - more like 33:3:3. The most important number to look at is the amount (if any) of slow-release nitrogen as a part of the total nitrogen. You can find this on the back of the bag in the section marked total analysis. Look for at least 8 percent to 15 percent of the nitrogen to be in a slow-release form. Slow-release nitrogen lasts longer and promotes more uniform greening and growth.

Fertilizer application rates for grass are based on delivering 1 pound of nitrogen per 1,000 square feet of turf with each application. A 33:3:3 formulation contains 33 percent nitrogen and will therefore require 3 pounds of that fertilizer for every 1,000 square feet of lawn to get the required 1 pound of nitrogen. How often this amount needs to be spread depends on the species of grass and the level of maintenance desired. Bermuda grass has a high nitrogen demand, once every eight to 10 weeks would be an adequate schedule for most home lawns.

Periodic applications of iron can improve turf color without giving additional leaf growth. Always use a rotary spreader for uniform fertilizer applications, never spread it by hand.

And finally, careful and responsible irrigation is necessary to keep your lawn in top shape. The worst irrigation schedule is five minutes each day. This leads to shallow root systems and weak turf. Soil type (clay or sand) plays an important factor in determining the best irrigation frequency. Clay soils have a large water holding capacity but may not drain well. With this soil, irrigate at least one to three times a week during dry summer periods. Each watering session should deliver one inch of water (650 gallons per 1,000 square feet), which is enough to wet clay soils to a depth of 12 to 15 inches. If water begins to run off before the required amount is finished, break up the session into two shorter time intervals for that day.

Sandy soils drain rapidly, have a smaller water holding capacity and will dry out more quickly than clay. For sandy soils, irrigate more often, maybe every two days, but for shorter periods of time. The best time to water any lawn is in the early morning hours when winds are likely to be low and water pressure is higher than during peak demand periods.