First of all, why should we care? Because most soils in areas of moderate to heavy rainfall are acidic. Many plants, including black walnut trees, are not at home in acidic soils. Black walnut treees, in fact, must have neutral soils if they are to grow at the optimum rate. A pH of 6.5 to 7.2 is ideal.*

To determine what your soil pH is you must have your soil analyzed. Numerous labs can do that for you. However, since you will also have to have your soil analyzed for nutrients, you should select a lab that knows what nutrients black walnuts need in order to grow well. (We recommend K Ag Labs, which you can reach at 800-356-6045.)

Second of all, exactly what is lime? The lime used for agricultural purposes is nothing more than agricultural limestone which has been ground. When mixed with soil of a low pH, lime will, over time, cause the resulting pH to rise. Obviously, it is important to apply the right amount of lime to the soil.

Lime generally comes in two varieties: ground limestone and pelletized. Of the two, the ground limestone is more commonly used. Ground limestone is less expensive and acts over a longer period of time...like years. When a farmer announces that it's time to lime the south forty, this is the lime he's refering to.

Pelletized lime is faster-acting than the ground limestone. The pellets are whitish, about the size of peas.

Third of all, how do I apply it? Broadcasting lime makes the most sense in any walnut plantation. Because you will want to raise the pH over the entire area where root systems are, or will be, broadcasting lime rather than applying lime at each tree makes more sense. Generally it will take one to three tons per acre, which should be good for three or four years, and lime can be applied any time of year.

When planting, mix some of the pelletized lime with the soil in the hole. How much depends on what the lab says you need, most likely between about a quarter and a half cup per tree. Then spread ground limestone around the tree in a circle roughly eight feet in diameter. A cup or two should be adequate in most areas, but once again, you should check the soil first.

*pH is the measure of a solution's acidity. 7.0 is neutral, 6.0 is mildly acidic, 5.0 is moderately acidic, 4.0 is very acidic, and so on. 8.0 is mildly basic (alkaline), 9.0 is moderately basic, 10.0 is very basic, and so on.