Improving Mineral Content By Using Limestone

By gardener | Oct 25, 2008

One of the best ways to solve many mineral problems you might have in your soil is to add finished compost or other partially decayed organic material. The effect on the mineral conditions of the soil is not immediate, but over time, adding organic matter helps to balance mineral content and even to modify soil pH.

There are other soil amendments you can add to correct specific pH and mineral imbalances. In most cases, you should only add these amendments according to recommendations from soil tests or plant analyses. You must be precise about adding natural mineral supplements, or you can create an excess of a particular nutrient. The excess may damage plants or may interfere with uptake of some other nutrients.

Correcting an Acid Soil: When soil pH is below 6.0, certain soil nutrients become less soluble, and therefore less available to most plants in the landscape. The exceptions to this are acid-loving plants such as hollies, blueberries, and rhododendrons, which are adapted to absorb their required amounts of needed nutrients from acid soils. Phosphorus and other major nutrients become locked into complex compounds that don’t readily break down or become available to most plants when the pH is less than 6.0.

Applying Lime: Limestones are minerals; they are the remains of primordial oceanic life, now mined out of quarries. Adding lime to the lawn and garden serves both to reduce the acidity (raise the pH) and to improve the soil structure and fertility. Limestone comes in several forms; the best one for home gardens is ground limestone.

There are two types of ground limestone: calcitic and dolomitic. Calcitic limestone releases calcium slowly in the soil. Dolomitic limestone slowly releases both calcium and magnesium. Choose the dolomitic type only if you know the soil has a magnesium deficiency. Otherwise, always use the calcitic limestone. Because ground limestone breaks down very slowly in the soil, you should apply it to the garden and lawn in the fall. That way you can assure its impact on the spring plants.

Lime not only increases pH, but also increases the bacterial activity in the soil, thereby speeding up the decomposition of organic matter. Consequently, if you add lime but not organic material to your soil, you will get good results in the first season. In subsequent years, productivity will not reach its full potential unless you also add more organic material.

A rule of thumb for most soils that have tested as acidic (pH less than 6.0) is to apply 5
pounds per 100 square feet to raise the pH by one point. Generally, sandy soils will need less limestone to change pH; clay soils will need more. The best time to test soil pH is in mid to late summer. That way, you can apply lime in the fall, and it will have time to act to correct pH before the next growing season. Retest the following summer to see if you need to repeat the
liming process.

In most situations, it’s easiest to apply lime with a small garden spreader. If you’re just applying it to a small area, you can broadcast it by hand and rake it into the soil surface.

Once your soil reaches the proper pH level, you only need to retest every three or four years. In high rainfall areas, pH will gradually decline over time, as calcium leaches downward through the soil.

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