Acid plants are peculiarly children of the forest glade, where the spongy leaf mold under the trees provides conditions to their liking. Or they may grow in pockets of woodsy soil on the side of a mountain. One condition they won’t tolerate is dryness, whether of root or leaf.
This need for moisture doesn’t end with the coming of freezing weather. The leaves are active the year around, giving off moisture even when the ground is frozen. Because of the high water needs, plus the need for air for the fungus on the roots, acid soil plants are seldom deep rooted. They produce their root mass so close to the surface that cultivation is taboo. Instead, we provide a mat of spongy organic matter which is kept moist, but never soggy.
While peat moss can be part of this mat, it cannot be the sole source of organic matter. Peat moss has reached a near-stable condition, with its active foods spent by decay. Fungi need starehes and sugars which can only come from decaying organic matter. The fungi extract this food and pass part of it on to the host plant.
In regions of bright sunshine, we find these plants growing largely under trees in light filtered shade. In the Midwest,” this is the only place for them. In general, acid soil plants do best at a pH of 4.5 to 5.0, quite a bit lower than that found commonly. This low pH requirement seems to be tied in with the need of the plant for large amounts of iron, available only at readings below 5.9. This assumes, of course, that the iron is actually in the soil. Merely lowering pH will not make available iron that isn’t there.
The chelated irons, which remain active longer than other iron compounds, have not supplied this element as well as was first supposed they would. The best form of iron seems to be ferrous ammonium sulfate; a mixture of two ounces of ammonium sulfate, two ounces ferrous sulfate dissolved in ten quarts of water makes a good solution of this to use on azaleas and other broad-leaved evergreens. Use this solution in place of water about once a month. The pH of the soil should be lowered, both to make iron remain in solution longer, and to favor the mycorrhizal fungi. This is easier to say than it is to do. We don’t seem to realize how stubbornly soil tries to return to its original reaction. The buffering capacity of soil is tremendous.