Rain Gardens Basics

What is a rain garden?

A rain garden is a shallow, planted depression designed to catch runoff from roofs, driveways, lanes or lawns and let it soak into the ground. It is not a pond and is not meant to hold water for long.

The planting and the soil work together to slow water, filter some pollutants and reduce the amount that rushes into ditches and streams. Extension programs in many states publish how-to manuals for homeowners.

Many people build one to solve a specific problem, such as a soggy spot below a downspout or erosion at the end of a lane. Defining the problem first helps you size and place the garden sensibly.

• Shallow planted dip for runoff
• Water soaks in within a short time
• Reduces erosion and flooding

Where should you put one?

Choose a spot that can receive runoff from a downspout or paved surface, in an area where water can soak in. Keep it well away from building foundations, septic systems, wells and steep unstable slopes, at distances recommended by local guidance.

Call your utility locating service before you dig, and avoid placing the garden over buried lines. Ask your local building or zoning office whether any rules apply to altering drainage.

• Place away from foundations, septic and wells
• Locate utilities before digging
• Check drainage rules

How do you check the soil and drainage?

The garden depends on soil that drains. Extension manuals describe simple infiltration tests, which show how quickly water soaks in. Very slow draining clay may need design changes or a different approach, and very high water tables can be a problem.

Do not guess. Follow the testing method in a trusted extension guide, or ask your conservation district to help. If the site drains poorly, ask for advice instead of forcing a design that will stay wet.

• Do a simple soak test
• Watch for standing water after storms
• Ask for help on clay or high water table sites

How big and how deep should it be?

Size depends on how much runoff arrives and how fast your soil drains. Extension manuals give methods for sizing based on the area draining to the garden, and typical depth is shallow so water drains soon after storms.

A flat bottom helps spread the water, and the edges need a gentle slope and a stable berm or lip where needed. Plan an overflow path so extra water in a large storm leaves the garden safely and away from buildings.

Plan early where excavated soil will go. Using it for a modest berm on the downhill side can save hauling, but spread any extra thinly so you do not create new drainage trouble.

• Size by drainage area and soil
• Keep it shallow with a flat bottom
• Plan a safe overflow route

What should you plant?

Plants should tolerate both wet and dry conditions, since the garden is flooded briefly and then dries. Native perennials, grasses and shrubs are often recommended, and deep roots help water move into the soil.

Use region-specific plant lists from your extension office or native plant society. Different zones in the garden, such as the wetter bottom and drier edges, suit different plants. Avoid invasive species.

Visit a local native plant nursery or your extension office for plant lists. A mix of heights and bloom times gives a better-looking garden and food for pollinators through the season.

• Choose plants tolerant of wet and dry
• Use native species where possible
• Match plants to bottom and edge zones

How do you build it step by step?

Mark the outline, call utilities, remove sod and dig to the planned depth, saving soil for the berm if needed. Loosen the bottom soil without compacting it, and keep heavy equipment out of the finished basin.

Plant, mulch with a type that will not float away, and water new plants until established. Seeds and small plants will need protection from weeds, so keep up with early weeding.

• Mark, locate utilities and dig
• Avoid compacting the bottom
• Mulch and water new plants

What maintenance and cautions apply?

Weed regularly in the first years, remove sediment and debris from inflow areas and check that the overflow works. If the garden holds water for days, check the soil and design again.

Standing water can breed mosquitoes if it persists. A properly functioning rain garden drains soon after storms, so persistent ponding is a sign to fix drainage. Keep children and pets away from deep or slow-draining basins, and ask your local health or mosquito control office about concerns.

• Weed and clear inflow areas
• Fix persistent standing water
• Check overflow after heavy storms

Last reviewed: November 12, 2026. Written by the Homestead & Small Farm Editorial Team. See our editorial policy.