Gardening glossary
Drainage
Drainage describes how readily water moves through soil and away from roots. Good drainage means excess water clears the root zone within a few hours, leaving behind moisture in the pore spaces but plenty of air. Poor drainage means water lingers, oxygen is displaced, and roots suffocate or rot.
The most common drainage failures I see: - Pots without drainage holes, or with holes blocked by a saucer of standing water. - Decorative cachepots used as primary pots, where excess water collects unseen at the bottom. - Heavy garden clay in low spots, where every irrigation pools. - "Drainage layers" of gravel at the bottom of pots — these actually raise the perched water table inside the pot and make drainage worse. Skip them.
How to test drainage in a bed: dig a hole 12 inches deep and wide, fill it with water, let it drain, then fill it again. If the second fill drains within 4 hours, drainage is good. 4-8 hours is workable for most plants. Over 8 hours means you need to amend, raise the bed, or pick plants that tolerate wet feet (cardinal flower, swamp milkweed, sweet flag).
How to improve drainage: - In containers: increase the perlite or pumice fraction to 20-40% and use a quality bagged mix rather than scoop-from-the-garden soil. - In raised beds: build up 8-12 inches above grade with a loam-like blend. - In heavy clay beds: dig in 2-4 inches of compost each season and avoid working the soil when it's wet (you'll compact it further). - Use terracotta pots for thirsty-when-it-suits-them plants like succulents — the clay wall lets moisture evaporate.
Watch for the warning signs of poor drainage: yellowing lower leaves, soft mushy stems at the base, fungus gnats swarming the surface, and a sour smell from the soil.