SOIL
The next is the most laborious but most vitally important part of the procedure—supplying suitable soil. Woods plants grow naturally in soil so rich in humus that it will hold many times its weight in water. Season after season the trees drop leaves, needles, twigs, and branches that decay and maintain the high level of humus, which contains micro-organisms that help sustain the plants. In our area and in most other woodsy sections, forest soil is very acid. But the loam in a cleared area adjoining the forest may contain little or no humus, and may not be nearly acid enough for the native plants growing a hundred feet away.
When a miniature woodland garden is planted in a wild, woodsy spot, the soil is probably suitable, and the trees will probably keep it that way. Then, you simply use plants that thrive naturally where the amount of available light, and the composition of the soil, are the same or similar. Otherwise, you need to prepare the soil thoroughly and deeply—a minimum of eight inches, and up to eighteen inches for small native shrubs.
You’ll need incredible quantities of leaf mold, very old manure, or composted leaves and grass. Over humus-poor soil, spread a layer of at least six inches, and mix it in by digging the soil and turning it over several times. At the same time, remove matted roots, stones, and other unwanted obstructions to planting. For a very small garden, you may find it simpler to remove all the soil to a depth of twelve to eighteen inches, and replace it completely with humus and leaf mold brought in from the woods or purchased for the purpose. Leaf mold, by the way, is the layer of partially decayed leaves immediately under the top layer of whole leaves; humus, in the next layer down, is more completely decayed. Don’t buy humus from door-to-door salesmen offering “big bargains.” This is a racket the police and Better Business Bureau are trying to extinguish. Buy only from a nurseryman you can trust.
While you’re conditioning soil, make sure there is good drainage. Only bog plants will grow with their roots in muck or standing water. You may need an initial layer of fine gravel or course sand. Raising the surface of the garden will also help.
If you think that the importance of suitable humus-rich soil is either exaggerated or overrated, think also of this: With the type of light and humus (usually acid) in which they grow naturally, woodland plants will settle down contentedly in your garden and establish families and colonies that increase every year. If you don’t provide it, they’ll get homesick and pine away. Not only that, but once they’ve made themselves at home, they’ll require practically no care. They don’t want to be cultivated, fertilized, weeded, watered, mulched, or given special protection in winter, as long as there are trees that drop leaves. The most you might have to do will be making sure the leaves aren’t blown away, or, if there are no trees, lugging in leaves from somewhere else.