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Does your lawn look pale? Does it have dead patches? Are the grass blades yellowing at the edges? If so, and if there's little thatch (dead grass under the green layer) and you can't see any signs of fungus, insects, or grubs, you might need to add some lime.

Lawns grow best in a soil with a neutral pH (i.e. neither acid nor alkaline). Soil pH - the quantity of hydrogen ions present - determines the amounts of nutrients available to the plants, and tends to become acid over time. This is due to the leaching out of calcium and magnesium, both of which make soil alkaline; repeated use of nitrogenous fertilisers; the use of organic matter such as compost; or the presence of sulphur in rainwater. Some soils are also acid by nature. If nothing else has worked to improve your lawn, and you can't account for its failure to thrive, you can purchase a pH testing kit from your local nursery or garden supply store. Several samples taken from different parts of the lawn will show whether pH is the problem.

If the soil test tells you your soil is acid, it's time for lime, a compound of calcium or calcium and magnesium. Not only does it counteract soil aciditiy, it also provides nutrients, reduces the solubility of potentially toxic elements such as aluminium and manganese, promotes the availability of plant nutrients including phosphorus, and improves soil structure. Calcic lime (calcium carbonate, CaCO3) is the usual choice, but dolomitic lime (equal parts calcium and magnesium carbonate) can be used if the lawn is lacking magnesium. Another lime is burnt or quick lime, which is faster acting and effective in half the quantity, but caustic. If using burnt lime, always wear gloves.

The best time to apply is before the lawn goes down, as it is absorbed very slowly. For an existing lawn that's ailing, try to add lime in late autumn, winter, or early spring. If you live in an area with cold winters, apply before the frosts; the freezing and thawing assist the lime's penetration into the soil. Avoid adding lime when the ground is very wet, as this makes an even distribution difficult.

Lime is can be bought in powder or pellet form; both leave dust, so a dust mask is advisable when applying either. Scatter by hand or use a spreader; be sure to apply it evenly across the lawn as lime does not move through the soil horizontally. The testing kit will tell you haw much lime to apply; this will depend on the acidity and the type of soil. Too much lime can be as bad as not enough; it should only be applied once every 3 to 5 years. If more than 150 pounds per 1,000 square feet are required, begin by applying half and recheck the pH 2 or 3 years later before adding any more. Water afterward to dissolve the lime and allow it to be absorbed by the soil.

Learn more about this author, Elizabeth Hedger.
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