Forest plants occur in horizontal layers from the sky to the ground, canopy trees exist overhead, understory trees and shrubs in between, and wildflowers, ferns and mosses on the ground. The forest floor often has a 4 – 8″ deep layer of loose, humus rich soil consisting of rotted leaves and twigs above a more solid soil. The humus and the soil underneath are acidic, varying from a pH of 4.0 – 6.9. This rich, acidic soil is the key to growing a successful woodland wildflower garden, but if you don’t have it, you can create it.
Plan your woodland garden in a place that already has a canopy of leaves, loose crumbly soil is often prefered. This may be in a natural woodland, in a small grove or group of trees, or even under one large, deep-rooted, wide-spreading tree.
Evaluate the soil by feeling it; if you can scrape the humus off the surface of the ground with your hands, it is an excellent site for a woodland garden. If the soil is hard, compacted, and root-filled, you will have to improve it. Poor soil results when tree leaves have been raked off and carted away year after year instead of being allowed to rot away naturally., or when the surface roots of the tree overhead have compacted the soil.
You can refurbish poor soil by spreading chopped leaves and twigs over the soil in a deep layer. Keep the leaves moist to aid in decomposition. Rotting leaves encourage earthworms, which will burrow through the existing soil loosening up the existing layers. You may have to do this for several years until you build up a deep enough layer to effectively plant in.
Once you’ve selected your site, clear out undesirable underbrush, invasive vines, and small saplings, but leave behind healthy, good-looking growth in strategic places underneath the tree. Trim off low-hanging branches and open up the canopy by thinning the trees so that dappled light has a chance to fall on the soil.
Lay out a path to meander among the trees, wood chips make a great natural looking path. The path gives structure to the garden and invites people to explore, without it people would walk all over your delicate plants. You can edge the path with a natural material, but an unedged path looks most natural.
Do not dig deeply or turn over the soil in a woodland site. Cultivating destroys the layers and disrupts the trees’ root system. Dig small, individual holes for flowers and ferns. You can dig planting holes for shrubs and small understory trees like dogwoods and azaleas, but do not excavate large areas or cut through large tree roots; plant somewhere else.
Woodland wildflowers are spring blooming, ephemeral plants. Most bloom before the overhead canopy of leaves has blocked out significant light, then they die to the ground by mid summer. If you add some ferns or hosta to your garden, their foliage sustains interest through late summer and fall, after the ephemerals die off for the year.
Arrange herbaceous perennials in groups under the trees and along the path edges, but do not set them out in rows. Take your cues from nature and don’t worry about leaving open space between the groups. Plant spreading types so they can roam freely and fill in to become swathes. Plant tap-rooted plants here and there so the ground-covering plants weave beneath taller plants.
Woodland plants always have a protective covering of humus over their roots, and so should yours. After planting, apply a loose covering of shredded leaves or humus around the wildflowers; don’t leave the soil exposed to drying sun and wind.
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