Slow-draining soils and low spots on a property can create unsightly and potentially foundation-damaging waterlogged soils that often need to be professionally dealt with. However, there are number of ways to improve garden and yard drainage yourself. Create a drainage plan for your garden based around two basic methods of controlling water. French drains are long, gravel-filled trenches that transport water away from poor-draining areas to dry-wells, which are deep, gravel-filled holes that give the water a place to drain and percolate into the ground.
Mark the planned layout for French drains and dry wells on the ground. Test the drainage of the soil in the areas you wish to dig a dry well by digging a 6 to 8-inch-wide vertical hole with a post hole digger to a depth of at least 4 feet. Fill the hole with 5 gallons of water and observe the speed at which the water drains. The water should drop 1 inch every three to five minutes for a dry well to work. If water drains more slowly, you can make dry wells larger. If the water does not drain from the hole after 24 hours, the French drains will need to drain to a hillside or street.
Dig the main French drain trench at least 12 inches deep and wide, starting from the low-ground where you wish the water to run. Place a plastic tarp next to the trench to place the removed soil on (you will have to remove most of this soil and dispose of it, as the trench will be filled almost completely with washed gravel).
Dig trenches so they have a grade that falls at least 1/4-inch per foot, to allow water to drain downhill. Dig auxiliary French drain trenches at 45 degree or 90 degree angles to the main trench.
Dig dry wells at 4 to 6 foot intervals along the bottom of the main French drain trench. Dig dry wells 6 to 8 inches wide and at least 4-feet deep using a posthole digger.
Tie one end of a 6-foot section of a 4-inch leach pipe fabric sleeve closed, making a sock shape. Place a shovel-full of washed gravel into the open end of the pipe sleeve, and lower the sleeve into the dry well hole.
Fill the fabric sleeve with washed gravel, until the fabric sock and dry well are 80-percent full. Tie the top of the fabric sleeve, tuck into the hole, and cover with additional gravel. Repeat the process until all dry wells are filled with leach-pipe fabric socks filled with washed gravel.
Line the bottom of the trench with at least 2 inches of washed rock or gravel. Place sheets of 48-inch landscape fabric over the crushed rock so the sides of the fabric extend upward in the trench in the shape of a U (landscape fabric acts as a filter, keeping dirt from clogging the drain). Place an additional inch of gravel on top of the fabric, then move the gravel around to retain the proper slope of the trench before laying any drain pipe.
Lay lengths of 4-inch corrugated leach pipe on top of the rock and fabric with the drainage holes on the pipe facing downward and use quick-connect 90-degree and 45-degree connectors to connect auxiliary French drains to the main French drain. Cover the exposed ends of the leach pipe with additional landscape fabric and secure it with tape.
Cover the entire length of leach pipe with 2 to 4 inches of washed, crushed rock. Wrap the protruding edges of the landscape fabric over top the pipe and gravel, wrapping them like a burrito. Fill the remainder of the trench with washed gravel to within 4 inches of grade.
Backfill the drainage trench with dirt from the tarp, placing at least 4 inches of top soil over the washed gravel, landscape fabric and drain pipe fill. Gently water the soil to settle it, then tamp the soil with the back of a shovel to compact it further. Use any leftover dirt from the tarp to add soil to low areas of your yard to bring the grade up and improve drainage.
Use the layout of the garden to your drainage plan's advantage, using natural slopes and gravity to move excess water. The larger the French drain trench you dig, the more efficient the drain will be. Larger French drains also require less maintenance in the long run; they take longer to become clogged with silt and soil. Use only washed rock, not merely crushed rock. Unwashed, crushed limestone hardens into a cement like stone over time. Line trenches with black plastic, or use pipe without drainage holes, to transport water past a problem area.
Always check with your local utility companies before you dig. Utility companies will come survey and mark your yard so you do not dig into water, gas or electrical lines.