For most US lawns, the most beneficial additive that can be applied isn’t fertilizer, it’s lime. Most homeowners know that it’s needed, but few know the importance of when, why, and how much.
As you can see from the chart, just about all of the regions in the US where grass is commonly grown are natively acidic. The blue areas are mostly arid desert and we can’t use the term “easy lawns” there.
Lime is applied to the soil to increase the soil pH. pH, a measure of the soil’s acidity or alkalinity, and can directly influence the vigor and quality of the home lawn. When the pH is below 7.0, the soil is said to be acidic; when above 7.0, it is alkaline.
When the pH drops below 6.0, the chemical reactions that supply some of the lawn’s nutrients can’t happen. It’s a form of malnutrition, the food might be there, but your lawn just can’t use it. Low pH limits your lawn’s ability to use nitrogen, phosphorus, potassium, sulfur, calcium, magnesium and molybdenum is restricted. The result is that your good looking fine grass’ growth is stunted and less desirable varieties or weeds or moss are able to take over.
Overly high pH can be just as bad. Alkali soil over pH 8.0 limits your lawns ability to use nitrogen, phosphorus, iron, manganese, boron, copper and zinc. Either way, too high or too low, and your lawn will start to show a loss of color, vigor, and tolerance for drought, heat, and stress.
Most soils tend to be acidic. Heavy rainfall and long time cultivation, combined with the type of soils left behind by the ice age, tend to leach the neutralizing minerals out of the ground. Of course, acid rain doesn’t help, and decomposing leaves add to the acid levels.
Fortunately, acidic soil is easy and moderately inexpensive to fix. Limestone is very common and it acts just like a giant Tums tablet when it’s applied to your law. It neutralizes acid and provides calcium and trace minerals at the same time.
Before you start, a soil test can tell you how much you will need. Don’t be surprised, it’s going to seem like a lot, but lime is inexpensive and, aside from carrying it home, it goes on easily. Your test will indicate how many pounds of pure calcium carbonate you will need per 1000 square feet. Since different types of limestone have slightly different contents, you’ll have to do a simple calculation. Use the table at the bottom of the page to determine how much you will need.
Lime can go on any time of the year when the ground isn’t frozen or the grass isn’t parched or wilted. It’s a good idea to water after application to wash it off the grass blades and before it blows away.
Lime Materials And Their Characteristics
|Material||Calcium carbonate equivalent||Rate of pH change||Max. recommended rate of application||Other comments|
|Burned Lime||180||Fast||10||Hazardous, difficult to apply|
|Dolomitic Limestone||70-95||Slow||50||Also a source of magnesium|
|Hydrated Lime||140||Fast||20||Hazardous, difficult to apply|
|Pelletized Limestone||70-95||Fast||50||Easy to apply, more expensive than other sources|
All values are approximate and vary by product.