Shade is seldom at a constant level throughout the day and across the seasons, so observation is essential. In a north-facing garden, the shade might be deep and constant close to the house, but less so farther away from it. Perhaps your yard is actually quite sunny, but a group of trees have created areas of shade.
As always, plants that are adapted to the conditions
will be the most successful, and are easily spotted. Reliably moist soil
in shade will open up opportunities for species that would naturally
grow at the edges of streams and ponds, while very dry shade will
require a different, more limited, range of plants.
Improving the Soil
The main problem in a shady garden tends to be the soil conditions. Trees growing in and around your garden require tremendous amounts of water and nutrients, and can leave the surrounding soil dry and barren. That said, if you are lucky enough to garden on the edge of old woodland, your soil will be enriched by leaf litter. Shade cast by a building, depending on the exposure, can result in soil that is either dry and thin or dank and structureless.
Soil pH can be affected by trees. A large pine tree, for example, can sometimes acidify the soil around it as its needles fall and rot down; this will affect the plants you can grow there. Nevertheless, all of these soil problems can be overcome with a little know-how and effort.
As most shade-tolerant plants originate from woodland environments, it makes sense to try to recreate similar conditions in your own garden by incorporating as much organic matter—composted bark, homemade leafmold and garden compost—into the soil as possible.
This can take time, especially under trees where roots prevent digging in compost to any depth. Here it is best to lay the compost on the surface as a mulch, and keep applying it every spring and fall so it breaks down slowly into the soil, or is drawn down by earthworms.
Letting in More Light
Reducing very dense shade vastly increases the number of plants you can grow. You can improve light levels in a number of simple ways.
Shade from buildings can be reduced by whitewashing the walls in order to reflect extra light into the garden.
Shade from dense tree canopies can be dealt with in the following ways:
- Thinning, which removes alternate branches.
- Pollarding, which involves regularly cutting back the main branches to the trunk or stem.
- Coppicing, which means the tree is cut down to ground level to promote multiple vigorous and decorative new shoots.
- Crown lifting, in which the lowest branches are removed to raise the height of the canopy.
Recognizing Shade-Loving Plants
As with sun-loving plants, shade-tolerant species have adapted over millennia to the conditions in which they grow. You can recognize shade-lovers by looking for the following traits:
- Flowering in spring or fall makes the most of the relatively high light and high rainfall when deciduous trees are leafless. Many bulbs use this strategy; they make the most of the short window of opportunity, flowering and replenishing their food stores, then spending the rest of the year dormant beneath ground.
- Dark pigmentation in leaves allows plants to photosynthesize more effectively when they are subjected to low light conditions. Many ericaceous (acid-loving) woodland plants, including camellias, have very dark green, glossy leaves.
- Large leaves help to maximize the surface area through which light is absorbed. The leaves of this evergreen bergenia are also thick and leathery, helping to reduce water loss.
- Densely packed leaves increase the light-collecting surface area. Some ferns, such as Polystichum setiferum, are also covered in hairs to trap moisture, so they can establish and survive in comparatively dry soil.