"Timing is everything," says Mike Goatley, turf guru at Virginia Tech in Blacksburg, Va.

"Fall is the optimal time to aggressively fertilize cool-season turf grasses — bluegrasses, fescues and ryegrasses."

The next few weeks are also the best timeframe for sowing new grass seed because autumn weather is still warm enough to promote germination. Then, cooler temperatures and plentiful rains enable roots to store food and grow deep before summer heat arrives again.

For warm-season grasses like Bermuda, Zoysia and Centipede, fall is still important — time to prep your yard for its winter nap.

Here's a quick rundown of what to do.

PREP YOUR PLACE. There is great value and peace of mind in having a yard professionally graded to get the best gradual slope for good drainage away from your home's foundation. A poorly graded yard contributes to moisture under your home; a roly-poly yard also pockets water and trips you as you walk or play in the grass. Bulk topsoil is needed to do major work while bagged topsoil is suitable for filling in minor problem areas.

Before seeding, soil benefits from a top-layer application of rich, aged compost. Spread about one half to one inch of organic matter you get in bulk from mulch suppliers, garden centers or composting facilities .

Once compost is down, use a core aerator to remove plugs of soil so your yard breathes better; frequent foot traffic and even heavy rains compact soil, making it difficult for oxygen and moisture to penetrate. Aeration also increases the activity of microorganisms that decompose thatch and improves rooting overall.

SEED or SOD THE SITE. Regular fall seeding keeps an existing lawn healthy and vigorous. Sow fescue at a rate of four to six pounds per 1,000 square feet and use a research university-evaluated and recommended seed. Many garden centers also offer their own seed blends, which are usually created from university recommendations.

If you choose to tear up an old lawn or face bare soil at a new house, sod is a quick way to get instant yard. Fall is an ideal time for laying sod, including warm-season Bermuda. Prepping soil for sod is the same as getting it ready for seed. Sod is easy for a do-it-yourself to put down, but install it within 24 hours because it is perishable. Newly installed sod needs to be thoroughly soaked daily for several weeks, or until you can tug at sections and feel that roots are penetrating existing soil.

FINE TUNE FERTILIZER. Too much of a good thing is often bad and lawn fertilizer is no exception. On grass, excessive nitrogen pushes top growth while reducing root growth, so you have a rich green veneer with a poor underground support system.

Instead of dumping bags of fertilizer — and money — on your yard, know what the soil needs through a test you conduct with a kit from your extension office. Soil testing should be done every three or four years; in addition to giving you clues to major and minor nutrient needs, it includes valuable information about soil acidity, which can be corrected with lime applications best done over winter.

August-November is the prime time for fertilizing a cool-season lawn. Make three applications, allowing 30 days between each; wait two weeks after fertilizing before you over seed an existing lawn.

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LOVE YOUR LAWN

—Good soil equals good lawn.

—Test soil for nutrient needs.

—Soil pH, or acidity, should be 6.2 to 6.5.

—Use corn meal gluten for spring-germinating weeds and crabgrass.

—Apply organic matter each fall to feed grass roots.

Source: "Going organic can be done at any time — even if you have already started your lawn-care plan."— Jan Perry-Weber, North Carolina cooperative extension

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QUICK FACTS

What's in a fertilizer? Three numbers — such as 12-4-8 or 46-0-0 — are listed on fertilizer bags. These numbers indicate, respectively, the percent of weight of nitrogen (N) for vigorous growth and green leaves; phosphorus (P) for development of roots, flowers and seeds; and potassium (K) for development of flowers and fruits and making plants resistant to wind, cold, drought and other stresses. When all three numbers of represented, a fertilizer is considered "complete."

Does your lawn need fertilizer? Instead of guessing, do a soil test to determine what nutrients are needed. Nitrogen recommendations, however, are not given in a soil test because nitrogen content is transient, according to Virginia Cooperative Extension; a rule of thumb is never apply more than 1 pound of soluble nitrogen per 1,000 square feet (multiply width times length) at a time. In fact, too much nitrogen weakens grass.

Hint: For dark green turf, a good alternative to nitrogen is periodic applications of iron.

Established lawns need minimum or sometimes no additional phosphorus but lime is often needed to maintain the soil's recommended acidity at a 6.2 to 6.5 pH (7.0 is neutral on the 0-14 pH scale). Again, too much lime is as harmful as too much fertilizer, so do a soil test to determine need. Changing soil acidity can take six to 12 months, so winter is the recommended application timeframe because the material can react in the soil before fall fertilization is done. If you use a urea, or a nitrogen-only fertilizer like a 46-0-0, wait three weeks before putting lime down or your nitrogen will be compromised by the increased pH around fertilizer granules, according to cooperative extension services.

Fertilizer options? Nothing benefits your lawn like a top layer of compost applied annually in the fall, according to Mike Goatley, turf specialist at Virginia Tech in Blacksburg, Va. Aged compost is naturally rich stuff — it slowly feeds turf roots, improves moisture retention, attracts beneficial micro-organisms and improves soil overall.

Yards that use compost need less water and fertilizer, according to nonprofit the Chesapeake Club, which promotes a lifestyle that benefits the Chesapeake Bay and its tributaries.

Grass clippings left on the lawn after mowing also do a lot of good work. Nitrogen and moisture from clippings return to the soil, again meaning you need less fertilizer.