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. A lawn aerator, available from tool rental companies, removes plugs of soil from your lawn to improve aeration and drainage. For a home lawn, one aeration each fall is usually enough. Aerate when the ground is soft enough to penetrate, but a little on the dry side to prevent compaction. Ideally, the machine should remove plugs about 2–3 inches (5–7.5cm) long, 0.5–0.75 in (1.25–1.9cm) in diameter. Pass over the lawn once or twice, or until there are eight or nine plugs per square foot (88-99 per m2). Leave the plugs on the lawn to decompose. If they're taking too long, break them up by dragging metal objects over the grass, or collect them to compost. Thatch is the spongy mat of roots and stems that build up on the lawn surface. Once it reaches 0.5 in (1.25 cm) thick, it will grow rapidly and prevent drainage and aeration. There are several ways to remove existing thatch:  The best way to remove thatch is additional core aeration, described above. Rent a dethatching machine to remove thatch less than 0.5 in (1.25 cm) thick. Do this only in early fall or late spring, when weather is cool and there are several weeks of growth left. Run a power rake over the lawn, frequently and shallowly. Deep power raking can cause damage. If thatch grows rapidly, try these fixes right after removing the existing thatch:   Topdress the lawn with a ⅛ in (3mm) sprinkle of soil, using the same soil as the lawn.  Conduct a soil test and adjust pH until it is between 6.0 and 7.0, or as recommended for your grass species. Add calcium carbonate lime to raise lawn pH, or sulfur to lower it.  Reduce use of pesticides, which may be killing earthworms that break down thatch. If water floods your lawn or runs off into surrounding areas, give the lawn half as much water as you currently use per session. Let the water drain for one hour, then give the lawn the rest of the water. This is usually a problem for dense clay soil and slopes.  Commercial wetting agents added to the water will reduce runoff, but won't fix a serious problem. If your lawn is seriously compacted or has a thick layer of thatch, aerate the yard as described above. Dew will not harm your grass, but "guttation" will. This is the formation of sugary water droplets along the blade edge, which attract disease and pests. To get rid of these, drag a hose or whipping pole over the surface, or hose them off with a brief spray. If your grass does poorly in shade make these adjustments to shaded areas:  Water less frequently but very deeply. Fertilize ⅓ or ½ as much as the sunny areas. Mow to 3 inches (7.5 cm) or higher. Reduce foot traffic. Minimize lawn use during frosts, when the lawn is vulnerable. If you need to break up ice, use as little salt as possible. Calcium chloride products are safer than sodium chloride or salt-laden snow.  Never use fertilizers to break up ice, as they will run off along with snowmelt and pollute water sources. Stick to light use in early spring until the grass dries out and revives. If there are bare spots, seed them early before weeds take hold.

Summary:
Aerate your yard once or twice a year Remove excessive thatch. Prevent future thatch buildup. Prevent surface runoff. Shake water droplets from grass surface. Improve poor grass in shady areas. Care for lawns in winter.