Q. How important is it to apply a winterizer type of fertilizer to your lawn?

A. Winterizer fertilizers typically contain less nitrogen and more potash than those applied during the growing season. Such a fertilizer may have an analysis on the order of 15-5-15. The analysis represents the percentage, by weight, of nitrogen, phosphate and potash. These are the macronutrients found in fertilizer, those that plants use in the greatest amount and that must be replenished most often.

Nitrogen is a component of chlorophyll. It is important for vegetative growth and strong root development. Phosphate is important for root growth and development in seedlings and for flowering and fruit set in more mature plants. Potash is important for overall vigor, disease resistance and cold hardiness. The idea of using a winterizer fertilizer is to increase the lawn's winter hardiness.

Research at Ohio State University suggests that a winterizer fertilizer may not be that important if you are growing Kentucky bluegrass, perennial ryegrass and/or fine fescues because they are perfectly winter hardy, even in the coldest parts of the state. However, if you grow zoysia or turf-type tall fescue -- grasses that are less winter hardy -- they may benefit from applying a fertilizer in the fall, usually from early to mid-October.

The hardier types of grass -- Kentucky bluegrass, perennial ryegrass and fine or creeping fescues -- benefit from a late-season application of quick-release nitrogen such as urea (46-0-0). This should be applied while the grass is still green but is no longer actively growing and before the ground freezes. Right around Thanksgiving is an ideal time to make this application in Western Pennsylvania. (And pushing a lawn spreader can help work off that Thanksgiving Day feast!)

This application helps extend the lawn's good green color into late fall and early winter. It also helps the lawn green up earlier in spring without applying fertilizer too early (which makes the spring growth spurt worse and opens the lawn to serious disease problems later in summer). Finally, because the grass is not actively growing, the nitrogen is used to enhance root and stem growth, which improves its drought tolerance and overall vigor.

Q. I have two beautiful hibiscus plants that have huge gorgeous flowers every year. Last year and this year, I noticed something eating the leaves, leaving them looking like lace. I cannot see anything on the leaves; maybe they are attacked at night? The plants look horrible in spite of those beautiful flowers. Can you tell me what is causing this damage and what I can do about it?

A. A small caterpillar-like insect is responsible for the damage. It can cause similar damage on hollyhocks and possibly other members of the cotton family. Although it can be called the hibiscus sawfly or the hollyhock sawfly, this particular insect has no generally accepted common name among entomologists. Its Latin name is Atomacera decepta.

The larva is the damaging stage of this pest. It is spiny and green, about 3/8 inch long with a black head. Because it is about the same shade of green as the leaves, it's easy to overlook. It resembles a caterpillar, but that term is reserved for the larvae of moths and butterflies.

Hibiscus sawfly is one of the most important pests to affect hibiscus plants, but it has not been studied extensively. There are several generations of this pest every year. Adults lay their eggs on the undersides of the leaves, generally toward the tip. The adults are small (less than ¹*₄ inch), fly-like insects that are black with an orange thorax. The larvae hatch and begin feeding, turning hibiscus and hollyhock leaves into lace. They pupate in debris around the base of the plant, then hatch out as adults.

Insecticide sprays are very effective in controlling this pest, but you have to scout your plants frequently for the damage and the larvae that cause it. There is nothing you can do right now to prevent the problem next year. Rotenone and pyrethrins, Sevin (carbaryl) and Bayer Advanced Garden Multi-Insect Killer (cyfluthrin) should provide adequate control. Begin making applications when you first notice damage. You will need to make repeated applications to control subsequent generations.

While looking up information for this article, I found the biological control agent Bt (Bacillius thuringiensis) being recommended to control hibiscus sawfly larvae. Bt does not work on the larvae of sawflies; it is only effective on true caterpillars.