Table of contents for Shaded Gardens
Continuously moist soil opens a whole world of possibilities for shade gardeners who are naturally drawn to mossy glens. In nature, you'll find wet, shaded sites along the banks of a tree-lined pool or stream, or in a low spot where rainwater collects after running down slopes. You may find soggy soil near a seasonal stream at the base of a steep slope, or where two gentle slopes converge. The soil is usually fertile in such spots because there is a natural accumulation of organic matter and all the water a plant could need. When shade is part of the bargain, there are many ways to turn a wet spot into a rich tapestry of color and texture, by adding bold, beautiful shade plants. Your challenge is to discover care-free plants, such as turtlehead, yellow flag iris, ferns, and woodland phlox, and to combine them with simple structures that will make the area equally hospitable to humans.
Before you begin making a garden in a wet spot, plan a pathway that is designed to assure safe footing. A series of steppingstones may be sufficient to get you from one place to another, or you might set steppingstones into a wider, more stable path lined with gravel. Another option is to build a elevated boardwalk that, surrounded by the foliage of your garden plants, appears to float mysteriously across the wetland. Choose a building material that works harmoniously with other materials present in your landscape. For example, you might build a brick walkway to echo the walls of a brick home. Or choose stone if there is a stone patio or wall nearby, or if natural stone outcroppings are part of the scene. Then, after the hard-scaping is in place, experiment cautiously when choosing plants, using promising ones on a small scale at first.
When you find a plant species that thrives in your wet, shady spot, add several of them. Many plants adapted to moist shade are very willing, on their own, to spread into lush colonies. Give them free reign to grow into drifts. Small drifts of slow-to-spread epimedium, lungwort, or turtlehead mimic the way they grow in nature. Remember that it's easier to care for a mass planting of one or two species than to tend to the whims of an assortment.
Between clumps of plants, allow open space to facilitate air circulation. Pathways that thread through a moist shade garden act as channels for health-giving light and air, and they even become drainage ditches during heavy rains.This decreases the likelihood of fungal diseases, which thrive in damp, stagnant air and standing water. You also may need to thin stems from time to time to open the center of shrubby plants to light and fresh air.
Keeping Soil Soft
Not only does wet soil drain slowly initially, but it is easily compacted by footsteps or even the pressure of pounding rain. To address both of these problems, consider building raised beds or natural-looking berms in a wet-shade garden. Plants appreciate the extra root space and improved drainage created when a bed is a few inches above surrounding moisture-laden soil. You can construct raised beds from various materials, including boards, landscaping timbers, brick, stone, or concrete blocks. In a wet site, it's a good idea to excavate a few inches of soil first, and then line the base of the bed with a 3 in (7.6 cm) deep layer of gravel. The gravel helps drain away excess water and forms an oxygen-rich zone for roots. After installing the frame, fill the bed with native soil mixed with compost and sand to further improve its texture and drainage. For a more natural appearance, build shallow berms using the same techniques described above.
Working Wet Soil
Whether you are simply making minor contour changes in your wet site, such as making a path, or taking on a larger project, such as constructing raised beds, it's important to work when the soil is relatively dry. Digging in very wet soil is unpleasant, and the soil tends to compact into hard clumps. A care-free reality is that naturally fertile soil that stays constantly moist may not require deep digging or the addition of soil amendments to make it hospitable to plants. If this is the case, simply place plants into planting holes rather than cultivating a large bed.
Whenever you are working in a damp or wet area, keep a pair of short boards handy to use as standing platforms while you plant, weed, or trim your garden plants. The boards will keep mud off your shoes and distribute your weight, reducing soil compaction. Having two boards, so that you can stand on one while moving the other to your next position, makes it easy to move between closely spaced plants without stepping on soil.