SOILS FOR ERICACEOUS PLANTS
Plants which prefer acid soils rarely need special soil treatment in areas where they grow naturally. When, however, the gardener in alkaline soil areas of the Middle West or California (to cite just two places) decides he must have azaleas, rhododendrons, blueberries or heather, a very real problem arises.
True, a soil pH as high as 6.9 can be pulled down with sulfur to 5.0 to enable such plants to survive. But maintaining such an acid soil in an alkaline area is often another matter. Surrounding soil will continue to be alkaline in reaction, and unless the site selected is on higher ground than the rest of the area, water runoff draining into the treated soil will bring in alkalinity to undo the gardener's efforts. Domestic tap water will usually be alkaline with a pH as high as the native soil or higher. This is particularly true in limestone country where ground water filters through limestone strata.
Among the worst offenders are earthworms (see Chapter Ten). They prefer an alkaline soil or at least one less acid than will support ericaceous plants. Even though the native alkaline soil is removed to a depth of two or three feet and replaced with earth high in acidifying materials, earthworms will continue to burrow through
this to reach the surface. Their burrows will be lined with limey slime brought from lower in the subsoil. Since most soils for ericaceous plants are high in organic matter, this helps feed the worms, which will pull half-decayed leaves, grass and other vegetation down into their burrows and mix it with limey soil to help digest it. I have seen a specially prepared area of rich acid soil ruined in two years by these pests.
The answer to earthworms is to dig out the pit to a depth of three feet and sprinkle chlordane over the bottom before refilling with acidified soil.
To counteract alkaline run-off into acidified soil, a ring or band of dusting sulfur perhaps a foot wide can be laid down around the treated area; drainage water must run through this sulfur strip.
Domestic water does not usually contain very much suspended matter, so if it is alkaline the amount of acidifying material needed to neutralize it is relatively small. Two ounces of sulfuric acid to 100 gallons of water is usually enough. If the planting is too large to be watered out of a barrel of treated water, there are devices which attach to the end of a hose; they withdraw a certain amount of sulfur solution out of a special container and mix it with tap water passing through the hose. Working out proportions to deliver two ounces of acid in each 100 gallons of water is a problem in simple arithmetic, once you know the proportioning ratio of the hose device.