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Rain gardens
A rain garden is a planted depression that takes roof or driveway runoff and lets it soak away. It is one of the few landscaping projects that solves a drainage problem, feeds pollinators and looks intentional.
Updated November 2026
Quick answer
A residential rain garden costs $1,500–$5,000 installed, or $10–$25 per square foot. Size it at roughly 10–20% of the roof area draining to it, keep it 10 feet from the foundation, and make sure it drains within 24–48 hours.
How it works
Runoff is directed into a shallow bowl — typically 6–12 inches deep — filled with amended soil and plants. Water ponds briefly, then infiltrates. The plants and soil filter sediment and nutrients, and the garden reduces the volume hitting storm drains. In combined-sewer cities, that also reduces overflow risk.
The critical test is infiltration. Dig a test hole, fill it with water, and see how fast it drains. If a hole holds water for more than a day, the site needs amendment, a underdrain or a different location. A rain garden that stays wet is a mosquito nursery, not a feature.
Sizing and siting
Size
Start with the roof area draining to the downspout, then take 10–20%. Sandy soil can take a smaller garden; clay needs a larger one or an underdrain. Depth is usually 6–12 inches, with a flat bottom and level edges.
Placement
Downslope and at least 10 feet from the foundation. Avoid utilities, septic fields, steep slopes and the drip line of a thirsty tree. Call 811 before digging.
Inlet
A buried downspout, a gravel channel or a shallow swale. Add a rock apron at the inlet to slow the flow and prevent scouring.
Overflow
Every rain garden needs a safe overflow path for extreme storms — a graded lip or a pipe to a lower area, not into the basement.
What to plant
Use regionally native perennials, sedges and grasses that tolerate both wet and dry periods. Three zones: a wet center (blue flag iris, sedges, swamp milkweed), a moist slope (cone flowers, joe-pye weed, asters) and a dry edge (little bluestem, butterfly weed, creeping phlox). Plant densely — bare soil is an invitation to weeds.
Do not use a rain garden as a dumping ground for lawn clippings or mulch. Both clog the surface and stop infiltration. A thin layer of shredded mulch is fine; a thick blanket is not.
Rain garden FAQ
What is a rain garden?
A shallow, planted depression that collects runoff from a roof, driveway or lawn and lets it soak into the soil instead of running to a storm drain. It is a landscape feature, not a pond: it should drain within 24–48 hours after a storm.
How much does a rain garden cost?
A contracted residential rain garden typically costs $1,500–$5,000, or about $10–$25 per square foot installed. A DIY build using a volunteer crew and smaller plants can be done for a few hundred dollars in materials.
How big should a rain garden be?
A common rule is 10–20% of the roof area draining to it, adjusted for soil and slope. For a 1,000 square foot roof, that is roughly 100–200 square feet of garden. A perc test or a simple infiltration check tells you whether the soil can take it.
Where should a rain garden go?
Downslope from the downspout, at least 10 feet from the foundation, away from utilities and septic fields, and not over a seasonally high water table. Call 811 before you dig.
Do rain gardens breed mosquitoes?
A functioning rain garden drains within a day or two, which is too short for a mosquito lifecycle. Standing water that persists for a week means the soil is compacted or the garden is undersized.