It’s the time of year to start thinking about making your lawn thicker and healthier. Fall is the best time of year to refurbish or plant cool season turf. It is the preferred ground cover that thrives in full sun and moist, well-drained soil rich in organic material.

Lawn grasses are specialized. They must withstand regular cutting at heights of one to four inches, be perennial, stay green most of the year and grow into a tight carpet that will hold up under foot traffic.

Turf grasses that fit these criteria have been divided into two types: warm and cool season. Fall is the time to establish or renew cool season grasses. Warm season grasses are brown in winter and don’t begin growing until average temperatures are higher than 60 degrees. We live on the northern cusp of hardiness for warm season grasses. They aren’t shade tolerant, but when growing well, they form dense mats that have a carpet-like texture. Warm season grasses should be planted in spring.

Cool season grasses stay green when temperatures are cool and turn brown during periods of drought and heat. Some will stay green through the winter. They are more suitable for this region, hold their chlorophyll longer and withstand our winters better. Even now, coming out of this summer’s dryness and heat, it took only one soaking rain and the onset of cooler temperatures for them to begin growing.

Pick a cool season grass seed by choosing between two types: dwarf, turf-type tall fescue or a fine-leafed variety, such as bluegrass, creeping red fescue and perennial rye grass hybrids.

Depending on your needs, you should consider a blend of several tall fescues or a mix of fine-textured grasses for seeding your lawn. Tall fescues — wear-tolerant and disease-resistant — are mowed to three or four inches in height. Fine-textured bluegrass, fine fescue, and perennial rye are softer to the touch. They can be mowed to a height of 21 / 2 inches and maintain a lush appearance.

Cool season turf responds well to feeding and seeding in the fall. Most cool season grasses grow best in soil that has a pH of 6.5 (pH is a measure of acidity and alkalinity; the lower the number, the more acidic the soil, the higher the number, the more alkaline). Check your soil’s pH with a test through your county cooperative extension service, which can tell you how to adjust the pH if needed, or get a pH meter at your local garden center. Also important for a healthy lawn are aeration, compost, seed and moisture.

Aerate with a plug aerator, a machine you can rent from an equipment and tool rental company such as Sunbelt Rentals, United Rentals or Ace Hardware. The spikes must be hollow and should take plugs of soil with each penetration. Most companies rent plug aerators for a minimum of a half day, which gives you enough time to go over the lawn three or four times, or more if needed. Never aerate lawns when they are soggy.

Condition the soil with compost whose texture is fine enough to fill the aeration holes. Sprinkle it about half an inch thick over the holes, making sure that you don’t cover healthy growing turf. Leafgro is a locally composted, fine-textured material. You might use as many as five bags of Leafgro per 1,000 square feet of turf if your lawn has a lot of bare areas. If you already have a thick lawn, you might need only one or two bags per 1,000 square feet. If you have poor soil, it is best to aerate and improve it with compost annually.

Fertilize a lawn during its strongest growing season. In September and October, for example, cool season grasses can use high nitrogen fertilizer because their leaves and roots grow vigorously until winter. Use a drop or broadcast spreader or spread by hand. Use a fertilizer that is at least 40 to 50 percent organic or has a percentage of slow-release or water-insoluble nitrogen. Always follow instructions on the packaging.

There is a fine-textured cool season seed mix that is blended for thickness, slow growth and low nutrient requirements called Pearl’s Premium Ultra Low Maintenance Grass Seed, Sun or Shade. The mix contains five species of slow growing native fescues, plus frontier perennial rye and deep blue Kentucky bluegrass — all of which have germinated and grown well in sun and light shade conditions in the Washington region. Because this seed mix is slow-growing, your lawn will need mowing only monthly during the growing season. Spread seed at a rate of five pounds per 1,000 square feet if you have mostly healthy lawn. If your lawn is thin, spread seed at eight to 10 pounds per 1,000 square feet.

Another disease- and wear-tolerant cool season grass is dwarf turf-type tall fescue. Over-seed existing lawns with three to four pounds per 1,000 square feet, using a blend of compact-growing tall fescues, such as Marathon blend seed or another blend of three or more seed varieties.

After you aerate, spread compost, fertilizer and seed. Ensure proper distribution of these amendments and break up soil plugs from the holes in your lawn by dragging an upside-down wire rake over the surface. And remember, lawns need five hours of direct sunlight or more to flourish.

Along with sun, all lawn care practices must be combined with water. Without it, nothing grows. With colder temperatures, moisture will begin to become available to plants in the form of dew. To be sure your newly aerated and amended lawn is moist enough, sprinkle the seed lightly with water every day (enough to moisten). As the seed begins to sprout, water more deeply but only once a week without rain. Tiny grass blades will begin to appear in one to two weeks, depending on the variety of grass seed you use and how well established the lawn is that you are nurturing.

Joel M. Lerner is president of Environmental Design in Capitol View Park, Md.