Poor drainage can be caused by several different conditions. Solutions to drainage problems depend on what is causing the problem, but some solutions solve several different problems.
Live With it
One solution is to decide to live with your drainage problem by making a water garden, pond, or bog in that location. Turn a persistent wet spot in the low part of your garden into a wetland, with bog plants and an intermittent pond. If necessary, excavate the soil and line the wet spot with plastic sheeting, then fill the soil in again. This will further impede drainage and make the intermittent wet spot a more permanent wet spot. A drip system can ensure it remains boggy even in dry spells.
A spring can be developed into a natural pool, birdbath, or small pond. Dig into the wet hillside to increase the flow of water, then lay a drain line to guide it to the surface. The line can spill into a basin to make a charming pool or birdbath.
If a wet spot is caused by a high water table, excavate to make it into a pond. If you dig away the mud, the excavation will fill with water, forming a natural pond.
Rise Above it
You can solve almost any drainage problem by raising the garden at that point. Raised beds and berms lift the soil above the water problem. Raised beds can be built on any surface, even the wettest. Make the walls of wood—such as railroad ties—or masonry as high as you wish or as necessary to lift the soil above the water. Waist-high beds are very easy to work in, and bring flowers close to eye level for better viewing.
Berms are mounds of soil. They look best when their slope gradually blends in with the soil level around them. Properly placed and constructed berms add interest to the garden and afford privacy and sound protection, too.
Dig Through it
Drainage problems created by layered soil can be solved by digging “wells” through the soil layers. Use a posthole digger to excavate through the layer next to trees or shrubs, or place holes every six feet or so apart in areas that will be lawns and vegetable gardens. Hardpan is harder to dig through than other types of layers. You might need to hire the job done by a contractor with a posthole digger mounted on a tractor.
Backfill the wells with the soil you removed from them. By stirring the layers together, you have improved the drainage in the holes and the soil around them.
Lighten it up
Heavy soil is most easily lightened by amending it with organic matter. Add lots—four to six inches—and dig it in as deep as possible. Each time you add amendments, the soil is further improved, so continue to add organic matter whenever possible.
Drain it off
If your problem stems from a high water table, or just too much water from some other source, the most satisfactory solution is to lay a system of drain lines to carry the water away. Simple drain lines can be installed by home gardeners with a lot of work. Complex ones, or those draining large properties, should be planned and installed by drainage experts.