Soil Testing Starts with pH

Soil testing for pH is almost as simple as measuring a yard with a ruler. Testing devices are sold by most gardening centers.

The simplest is merely a strip of paper which one pushes down into the damp soil. If it doesn’t change color, the soil is 7, or neutral. If it turns pink the soil is acid; if blue, it is alkaline.



The inexpensive testing kits are more accurate because they give the degree of acidity or alkalinity of the soil.

Dig up a specimen of soil, using a tool that has not come in contact with fertilizer or compost. I like a clean spoon.

Digging about four inches down and being careful not to touch the sample with your hands (they have an acid reaction, you know), put a tiny amount into a test tube, then an equal amount of solution. Cover the tube and shake vigorously.

Let the soil settle, then examine for color the liquid above it. You are given a color chart with which to compare it if it is hunter’s green your soil is slightly alkaline; light green, about 6.5 on the acidity scale, only a half degree less than neutral; daffodil-yellow, 6; pink, 5.25 pH; tomato red, 4.5 pH.

Of greatest value to any gardener is the chart that comes with the kit, telling exactly at what acidity each plant in the garden will do its best. No guesswork here, you learn exactly what you have in pH and what you need to get best results.

As gardeners we spend so much of our lives guessing and approximating; it’s a downright comfort to have something we can be really sure of.

Now that you know the score, what to do about it?

A too acid soil will benefit by a dose of limestone. I like the dolomite best because it contains magnesium which is necessary for plants and often lacking. Or you may use wood ashes, crushed limestone or ground oyster shells.

A little at a time here, please. Like salt in the soup it’s easier to put it in than to get it out again if you’ve used too much.

Horticulturists advise one to go up or down one step at a time; if your soil is 4.5 raise it to 5.5 this year, then go after it again next. If your soil is sandy, 30 pounds of lime per thousand square feet is enough; if it’s heavy clay you can safely use 80 pounds per thousand.

Wait a little after you apply it, then test again. It takes several months, sometimes a full year, for the whole effect of liming to become apparent.

What if your soil tests too high, is alkaline?

Sulfur does an excellent job. Comparatively little is necessary to lower the pH one point; one tablespoonful for every five square feet will do it. Instead of using sulfur many gardeners prefer a mulch of peat, sawdust or pine needles or compost made largely of leaves.

If you are satisfied in general with the pH of your soil but would like to grow a few acid lovers like azaleas, rhododendrons or gardenias you can easily accommodate them with little islands of acidity by digging out part of the soil around them and replacing it with compost, peat or leaf mold, or a mixture of them.

I have many of these little islands of special soil here and there in my garden. Test each separately whenever you feel dubious about it, and give it more peat or leaf mold as it shows a deficiency.