Loren, of Honolulu, writes about a common local lawn situation:

Last February, his family moved into a house with a very large backyard. Most of it is composed of several different lawn grasses. He has identified three types of zoysia — El Toro, emerald and temple grass — along with Bermuda grass and some other grassy weeds, including Hilo grass and nutgrass. There is also the usual collection of broadleaf weeds. Most of the lawn gets sun all day except under two medium trees, where the emerald zoysia and Hilo grass do well.

Loren does not want to replace the entire yard but would like to work with what is there to eventually have a nice looking, weed-free lawn.

In cases like Loren's, where total lawn replacement is not practical, the best option is to put your efforts into eliminating the weeds and let the desirable lawn grasses coexist. In this case, the three zoysias and the Bermuda grass mix will blend reasonably well. This will also be an advantage in the shadier areas, where the zoysia will perform better than Bermuda grass.

It is very important to maintain a regular and timely mowing schedule, and to select the most desirable height of cut. With this particular mix of grasses, a mowing height of about one inch or a little higher will probably work best. That will be the lowest or next-to-lowest height setting on most rotary mowers. The growth rate will be slower during the winter months, but regular mowing to remove not more than one-third of the blades is always recommended.

A careful spraying program of selective herbicides and fertilization can gradually control the weed problem and allow the grasses to cover. Begin with an application of turf fertilizer, preferably one with slow-release nitrogen, at a rate of 1 pound of nitrogen per 1,000 square feet of lawn. This will help to get the grass healthy and more able to withstand the following herbicide treatments. At the same time, the rapidly growing weeds will be more susceptible. Begin the herbicide program when the lawn responds to the fertilizer. Several different herbicides will be necessary to control all of the weeds and at the same time not injure the lawn grasses. There are three basic types of selective herbicides: those that kill only broadleaf plants, those that kill only sedges (nutgrass, McCoy grass and kylinga are the most common) and those that kill only grass.

There are many broadleaf herbicides available in garden shops. Weed B Gone makes a variety of products. Another readily available product is Trimec for Southern lawns, which controls many broadleaf weeds. Read the label to choose the right product for your type of lawn and weeds you want to kill.

Nutgrass and other sedge-type weeds are best controlled with a product called Image or another called Sedge Hammer. Both are safe to apply to most turf grasses.

A selective crabgrass-type herbicide can be used to keep Hilo grass and other wide-bladed grasses under control. These products contain an active ingredient called MSMA and are safe to apply to zoysia and Bermuda grass lawns. The most commonly available product is Monterey Weed Hoe. A Trimec product called Trimec Plus also contains MSMA and is effective in controlling both broadleaf and grassy weeds.

For very hard-to-control weeds, a direct application of Roundup is sometimes the only effective method. In lawn areas, where spot spraying will kill too much grass around the treated area, a narrow watercolor paintbrush can be used to paint a small amount of concentrated Roundup (1 to 10 dilution) directly onto a portion of the weed. Mix in a green turf dye to better visualize and ensure good coverage. This can be tedious work but eventually will eliminate the more troublesome spreading type woody weeds such as sleeping grass.

Lawn renovations such as this should be long-term projects. Constant evaluation leading to possible changes in direction may be necessary as grasses blend together and the weeds are brought under control.

Jay Deputy is an education specialist in landscape horticulture and turf at the University of Hawai'i-Manoa Department of Tropical Plant and Soil Sciences, and state administrator for the Certified Landscape Technician program. Got a lawn care or turf question? Write to deputy@hawaii.edu.