The bottom of a bog should be watertight. However, the top foot of a bog requires a bit of drainage. Simply poke or drill small holes through the liner at regular intervals along all sides of the top 12 inches (30.5 centimeters) of the trench. This will keep a bog's topsoil relatively dry and ensure that the crowns of plants don't freeze or rot [source: Burrell].
Because a bog needs to stay evenly moist at all times, it's important to integrate a method of watering into the bog design. Here are three simple ways to keep a bog garden moist:
- Install perforated PVC piping at each corner of your trench, leaving a couple of inches sticking up above the surface. Place your hose, rain barrel siphon or other water source into the above-ground end. Plug the buried end of the pipe, and water will seep out slowly and evenly from the perforations.
- If you need an even more subtle watering method, place a smaller perforated pipe inside a larger one and fill the space between with gravel. This reduces flow to a bare trickle. Remember to plug the buried end.
- Run rigid perforated piping horizontally along the bottom of the trench and connect it with an elbow to one of the two types of vertical perforated piping as described above. Cover the horizontal pipe with gravel to keep the drainage holes from becoming clogged with soil, and make sure to plug the buried end [source: Burrell].
Many true bog plants are adapted to thrive in poor, nutrient-deprived soil; standard compost is generally too rich for them. If you want to cultivate bog-adapted plants, most sources suggest filling the bog with a mixture of peat moss and sand [source: Fisher]. However, a wide array of non-specialized bulbs, perennials and shrubs can also thrive in constantly moist conditions. If these are the plants you want to grow, fill your bog garden with a mixture of 50 percent excavated soil and 50 percent compost [source: Burrell].
The type of soil you choose will depend on the kinds of plants your bog will support. In the next section, we'll explore different kinds of plants that work well in bog gardens.