If you go away on vacation for more than two weeks, try to have someone cut the lawn grass for you. It can prevent some serious problems.

When the grass gets quite tall, the lower portion of the stems turn white due to lack of chlorophyll. The grass blades are close together, shading one another, and there isn't enough light.

If all or almost all of the green part is cut off when you mow, it reduces food production, During tests at Michigan State, a single clipping caused root growth to stop for period ranging from six to 18 days.

Root growth usually stopped within 24 hours and didn't start again until top growth was well advanced. A second clipping soon afterward, also removing most of the green part, caused root growth to stop for periods ranging from 25 to 45 days.

When the grass gets quite tall, don't try to return it to the normal height with one mowing. If the normal mowing height is about two inches and the grass has grown to four inches, take off one inch with the first cutting, and four or five days later take off another inch. Then about a week later, resume mowing at the regular two-inch height.

One of the most important things for a good lawn is fro the grass to have an adequate root system. It helps the grass tolerate weather too hot or too cold, too much or too little moisture, and insufficient nutrients. It provides a considerable degree of disease resistance.

To stay green and attractive, a lawn usually needs more water during the summer than at other times of the year. Temperatures are higher and rainfall is often inadequate. Bentgrasses and Bermudagrasses usually need to be watered more often than other kinds. Bluegrasses, fescues and zoysia are more tolerant of a moisture deficeincy. They may turn brown with prolonged drought but quickly recover when the rains come.

The amount of water required by each grass will vary from lawn to lawn. Sandy soils hold about half an inch of water per foot of depth, loamy soils about one inch per foot and loams and clays will need four times as much -- but on the other hand can go four times as long without being watered.

The lawn should be watered when the soil begins to dry out. When you water, do it thououghly. Sprinkling for 10 or 15 minutes at frequent intervals encourages shallow rooting and can cause trouble.

Q. Our lawn is a mess, mostly weeds. We are thinking about putting in zoysia. Is it a good idea?

A: Meyer zoysia has dark green leaves that closely resemble Merion Kentucky, a dense turf that's resistant to wear and weeds and has some resistance to insects and diseases. Certified plugs or sprigs should be used and should be planted no later than August 1 to become established before cold weather starts. The first killing frost causes it to turn brown in the fall, and it's slow to become green in the spring. William H. Daniel, Purdue University turf specialist, says it has as much rejuvenation as any grass. "I think there are a hundred gold-course fairways of zoysia in Kansas City," he says, and a friend who has a zoysia lawn in Northern Michigan says it suits him fine.

Q: My tomato plants have good size tomatoes on them, but some have a rotten spot on the end. What is the cause and what should I do to stop it?

A: It's called blossom-end rot, and the primary cause if lack of calcium in the fruit -- which, in turn, is often due to lack of rainfall or inadequate watering. Tomatoes need at least an inch of rainfall or watering each week. Sprinkling them 10 or 15 minutes every few days does no good, since the water does not go deep enough.

Q: My compost pile smells awful. What causes it and what can I do about it?

A: With too much moisture and poor drainage, the compost pile stays soggy wet and air is excluded. Air should penetrate the entire compost heap to allow microbes to act and finish the compost in minumum time. With poor drainage, decay slows down and offensive odors occur. With good aeration the disagreeable smell will soom be gone. Turning the pile with a pitchfork will improve aeration.

Q: How can I get rid of little white bits on my African violets? What are they?

A: They are probably mealybugs (insects). They get to be about 3/16th of an inch long, and are ususally in the axils or crawling on stems and leaves. They can be picked off by hand or wiped off with a cloth that has been soaked in rubbing alcohol. The alcohol will kill them without hurting the plant. Repeated treatments may be necessary because of eggs hatching.

Q: Is there a way to get rid of weeks in my vegetable garden without spraying with poisonous chemicals?

A: Using discarded newspapers can help keep the weeds under control. Spread them over the gound as a mulch. Use several thicknesses that will withstand rainfall over much of the season, and anchor them with soil to keep the wind from blowing them away.

Q: Is it true that if you smoke cigarettes around tomato plants you may damage them?

A: You may give them a virus disease called tobacco mosiac. It causes yellow or light-green mottling and some curling of leaves, and a greatly reduced crop. Tobacco chewers also can spread the disease. If you have been smoking or shewing, better wash you hands with milk before handling the tomato plants.

Q: We had a chance to get some topsoil cheap, and we piled it up about five feet deep around two of our trees.Will it hurt them?

A: It can prevent air (oxygen) from reaching the roots and thereby cause serious damage. Sugar maple, dogwood, oak, tulip tree and most evergreens suffer most, birch, hickory and hemlock suffer less, and elm, sycamore, poplar, willow, pin oak and locust are least affected.

Q: Our two Bartlett pear trees get many blossoms but no pears. How come?

A: Pollination is the problem. Bartlett pears bear little or no fruit unless crosspollinated with another variety. Duchess d'Angouleme is considered good as a pollinator for Bartlett. Rainy weather when the tree is in bloom also may prevent pollination.

Q: My cucumber vines were loaded with blossoms and tiny cucumbers when one after another they wilted and died. The same thing happened last year. The squash vines growing nearby did the same thime. What caused it?

A: It was due to the squash vine borer, a small caterpillar that attacks squash, pumpkin, gourd, cucumber and muskmelon. Dusting the stems with methoxychlor powder may save the plants. Follow directions on the label for application.