SPRING
aerate
rake thatch
test the soil pH
topdress
overseed
fertilize late, if at all

SUMMER
mow high & often
leave clippings on the lawn; don't fertilize
water properly, if at all
combat weeds intelligently
renovate lawn in late summer

FALL
mow your leaves
aerate
fertilize
overseed bare spots & "old" lawns

WINTER
wait!
winterize your mower
get out your snow shovel
see the nyc compost calendar for any winter workshops that might be of interest

AERATE

Research suggests that compaction is the prime cause of weed growth. Lawns fed with a steady diet of chemicals often suffer from compaction, since the aerating organisms, such as earthworms, have been eliminated. Old lawns or those exposed to heavy traffic are also likely to be compacted. When soil is compacted, water and nutrients can't reach the turf roots and the hardened soil prevents roots from penetrating the ground. Consequently, bare areas open up and opportunistic weeds move in.

It is best to wait until the ground is relatively dry before aerating—otherwise, you'll end up with a muddy mess. There are several different tools available for aerating. For a large area, you can rent a power aerator. Smaller tools include hand-and-foot powered aerators, or aerator footwear that you put on while walking over the yard. If you use a core aerator, leave the plugs on the surface. They will help break down thatch.

RAKE THATCH

Raking thatch, or dethatching, is the process of removing dead organic matter from your lawn. If there's a build-up of dead surface roots and woody fibrous material, then you need to dethatch. Dethatching is critical if your lawn is made up of a sod-forming species of grass, such as Kentucky bluegrass, or if you've over-watered or over-fertilized in the past. Up to a half inch layer of grass clippings, however, can be beneficial for your lawn, because it retains water and protects root systems.

Wait for the ground to be somewhat dry before dethatching, since dethatching is an aggressive process that can pull grass out by the roots if the soil is wet. Tools for dethatching include a dethatching attachment for the front of your mower or a metal dethatching rake. Be sure to save any organic material for your compost pile.

TEST SOIL pH

It is important to test the pH of your soil, since grass species grow at a pH between 6.5 and 7.0. Here in the Northeast, soil is usually slightly acidic and needs to be amended with an application of lime, but test first, because local conditions can vary. Do not apply lime without knowing the pH of your soil! Cornell Nutrient Analysis Lab can test the pH of your soil, or you can buy a do-it-yourself kit from Solvita or most home and garden stores.

TOPDRESS

Topdressing is the practice of covering the turf with an eighth-inch to a quarter-inch layer of weed-free topsoil or screened organic compost. Topdressing is especially helpful in resuscitating lawns previously sterilized by chemical use.

The perfect time to topdress is just after aerating, filling those tiny holes with loose, rich organic material. New York City residents can pick up 30 gallons of free, screened organic compost each spring and fall at compost givebacks sponsored by the Department of Sanitation.

FERTILIZE

Never fertilize too early in the season. A common misunderstanding is that spring is the time to fertilize, but grass will green-up and grow naturally in the spring. Fertilizing in the summer is not recommended, since it encourages weeds to overwhelm the grass when it is most vulnerable. By simply leaving the grass clippings on your lawn after mowing in the summer, you provide your lawn with 25% of the total nitrogen it needs.

The best time to fertilize is in the fall. Try to choose natural and organic fertilizers even if they sometimes cost more in the short term, since natural or organic fertilizers release more nutrients in the long run.

Testing your soil will help you determine what fertilizing is needed, if any:

• Nitrogen (N) promotes growth and good color. If your soil tests reveal that your soil has a low organic matter content, you can increase nitrogen in your soil with organic composted cow manure, or fish or seaweed foliar sprays.

• Phosphorous (P) promotes strong roots and help plants to flower. If your soil test indicates a phosphorous deficiency, you can spread rock phosphate or bonemeal.

• Potassium (K) promotes the flow of nutrients through plants and helps plants withstand stress such as drought, insect damage, or extreme temperatures. An organic source of potassium is Sul-po-mag (0-0-22), the commercial name for the mined mineral sulfate of potash-magnesia.

MOW HIGH

Mowing height is important, especially during the hottest months of the summer. As a general rule, mow high and mow often. Mowing grass too close to the ground increases the vulnerability of grass to the hot sun, exposes delectable parts to insects, and weakens the root system. The growth of new green grass is hindered because the plant directs its energy towards the struggling roots. Mowing higher also helps control weeds like crabgrass by "shading" them out. For every eighth-inch that a lawnmower blade is raised, there is a 30% increase in the leaf surface area. That means a relative increase in photosynthesis, which feeds a larger, healthier root system.

You can maximize the health of most grass species by letting grass grow to four inches and mowing it to three inches. Never mow off more than one-third of the grass blade length. Keep mower blades sharp. Consider buying an extra set to use while the other set is being sharpened. Grass cut with dull blades is jagged and irregular, which promotes moisture loss and increases recovery time. Sharpened blades make a clean cut that allows for faster recovery.

WATER PROPERLY, IF AT ALL

Watering improperly during the summer can do your lawn more harm than good. Many people let their lawns become dormant during hot months rather than water them incorrectly. This conserves water when it is most needed for other, more important uses. A healthy lawn will bounce back when weather conditions change in the fall.

If you decide to water, water deeply, so that roots have to push deep into the soil to reach the water. Briefly sprinkling your lawn on a hot summer day only moistens the surface, permitting roots to soak up nutrients from the top few inches of soil. This results in a weak, shallow-rooted lawn.

Lawns need a total of one inch of water per week, including rainfall. If your soil holds water well, watering for at least an hour every week to ten days is sufficient. Water twice as often in sandy areas, or when temperatures stay in the 90°sF for more than three days. To prevent waste through evaporation, water in the early morning, before 9 am.

COMBAT WEEDS

The first step in combating weeds to realize that they are merely misplaced wild plants—nature's way of promoting diversity and balance. In some cases, weeds are beneficial. Dandelions, for example, have very deep roots that bring leached nutrients up to the surface. Clover is a legume, a plant that captures free nitrogen from the atmosphere and shares it with grass. Because of these unique traits, both dandelions and clover can survive a harsh drought and stay green long after grass has turned brown.

Weeds can also be indicators of lawn problems, however. Crabgrass thrives in sandy soil that drains too quickly. And dandelions favor compacted soil that is slightly acidic. If you are plagued with a particular species of weed, save a sample for identification by a landscape professional, one of the City's Botanical Gardens, or the Cornell Cooperative Extension. By remedying the factors that encourage weed growth, you can prevent or eliminate weed problems and improve the overall health of the soil ecosystem. To remove existing weeds, get to the root of the problem—that is, be sure to pull up the main root, sometimes called the tap root, to ensure that the plant doesn't grow back.

RENOVATE YOUR LAWN

Thought late summer was too late to start working on your lawn? Not so. Here in the Northeast, mid-August through the end of September is the best time to build the health of your lawn. Warm temperatures help seeds to grow. In addition, grass planted in the late summer will be well established for almost a year before it has to combat stress caused by the next summer's sun.

If there are large sections of your lawn thoroughly plagued by brown spots and weeds, you may want to consider starting from scratch—removing all of the existing grass in that area and beginning anew. You can remove the existing turf by digging it up or tilling it under, then raking up and removing the clumps. A less labor-intensive method is to cover the area with black plastic until all of the grass is dead, which conserves topsoil while creating organic matter. Till 2 to 3 inches of compost into the top 5 to 6 inches of lawn to alleviate drainage problems and maximize the amount of nutrients available to turf.

Choose seed to complement the soil and climate. For help deciding how to integrate different species and cultivars, contact your local Cornell Cooperative Extension or a landscaping expert. Here in the Northeast, four main turfgrass species are recommended: Perennial Ryegrass, Tall Fescue, Fine Fescue, and Kentucky Bluegrass.

MOW YOUR LEAVES

Unlike grass clippings left on the lawn during summer, dry leaves from deciduous trees are not a source of nitrogen or moisture. Thick layers of fallen leaves, especially when they are wet and compact, block light and air and suffocate grass underneath. But fallen leaves do contain carbon and other nutrients and add considerable organic matter to the soil. By mowing the leaves on your lawn, you shred them into smaller pieces that microorganisms can break down more quickly. This prevents excessive amounts of leaves from settling and becoming an impenetrable matted layer.

You can also rake leaves up, bag them, and keep them on hand as a source of "browns" to balance out "greens" in your compost bin over the winter. If you have more leaves than you can mow or store, place them out at the curb (in clear bags) during the Department of Sanitation's special fall leaf collection program. See the DOS website for all special collection dates and procedures at www.nyc.gov/sanitation.