Good drainage is essential in a garden not only for practical reasons — no one wants puddles outside the back door — but also for the benefit of plants, as they may suffer in poorly drained areas.

Poor drainage may be caused by soil compaction, a common problem around new homes, impermeable clay subsoil, or hardpan. Learn what type of soil you have, and also make a note of low spots and wet areas.


Grading is the movement of soil. When dealing with garden design, grading provides drainage for surface water, areas for play, and paths for movement within the garden. Always consider the effects on drainage when grading for any purpose. After drainage, terracing to increase the amount of flat land is the most common reason to undertake grading activities.

While it is important for the homeowner to plan and visualize the results of potential grading changes, it is best to consult with professionals for significant grading projects. Contact your local planning department to learn about the possible need for permits.

Level or Sloped

Few properties are perfectly level. The slope (steepness) may be only a few inches from end to end or so severe that it’s difficult to walk up and down the property. To make the most of your property, ask yourself the following questions:

  • Does your property have a slope? The existing slope will determine what actions should be taken. Ground covers may be the answer for long, gentle slopes. Most ground covers (not grass) will probably stabilize a 1:2 (1 foot of rise per 2 feet of run) to 1:3 slope. Lawn or bark mulch should not be placed on a slope with a ratio greater than 1 foot of rise per 2 feet of run.

Natural stone blends the upper and lower gardens beautifully.


If you've followed the steps listed on the Soil page to improve your soil and you still have poor drainage, you may need to install a subsurface drain system to carry away excess water.

Stone steps

Known as a French drain, this system consists of lengths of perforated drainpipe which is installed at a slight slope to facilitate drainage in a gravel-filled trench. Wrap the pipe with filter fabric prior to installing it in the gravel. If the perforated holes are on one side of the pipe, be sure to place pipe with the holes pointing down into the gravel.

A French drain was installed beneath this garden. The site was originally a parking lot of compacted soil. Mulch added to the site’s soil produced a flurry of flowers.
Design: Ali Davidson, Landscape Architect, Petaluma, CA.
French drain