What to check first
Trace the water during rain
Watch where roof and paved-area runoff travels, where it pools and where an overflow would go. Sketch the contributing surfaces and possible garden locations. A basin must have a safe overflow route that does not direct water toward foundations or neighboring property. [2]
Check setbacks and buried services
Mark buildings, property boundaries, wells, septic areas and major tree roots. Extension examples commonly start at ten feet from foundations, but slope and local requirements can call for more. Use your state's utility-location service before digging any test hole or garden. [1]
Distinguish an infiltration site from a wetland
Persistent saturation or water that remains for days suggests a different problem from temporary runoff. UMass identifies wetland soil indicators and poor drainage as reasons to reconsider the location or design. Do not assume an existing wet area is available to excavate or fill. [3]
Choose the next step for your plant
Compare candidate locations before choosing plants
Favor a feasible runoff-interception spot with room for the required separation and maintenance access. Avoid steep-slope edges, existing or reserve septic areas, utilities and high-groundwater locations. If the constraints leave no suitable space, ask the local stormwater or conservation office about alternatives. [2]
Use the locally recommended infiltration test
Follow the local test procedure and record the hole dimensions, weather and drainage result. Minnesota and Massachusetts describe different screening tests, so their thresholds should not be mixed. A slow result warrants another location or professional design advice, not an improvised gravel-filled pit. [1] [3]
What to avoid
- Do not excavate an existing wetland or redirect runoff into it without guidance from the responsible local authority.
- Do not treat a setback quoted for another state as approval for your property.
What to watch next
Take your sketch and drainage observations to the local stormwater program if the site is near a well, wetland, septic system, slope or foundation. Confirm the location and overflow design before purchasing plants. A planting list cannot resolve an unsuitable drainage site.
Common questions
Should the rain garden hold water all the time?
An ordinary infiltration rain garden collects water temporarily and drains between storms. A permanently wet garden has different soil, plant and design needs. Existing persistent ponding should be assessed rather than assumed to be the ideal location. [3]
Is passing a simple drainage test enough?
No. Infiltration is only one check. The location must also meet applicable setbacks, avoid buried services and provide safe overflow. Runoff quantity, groundwater and slope can change whether a basic home-garden approach is appropriate. [2] [1]
Sources and review
This guide was prepared with AI assistance and checked against the sources below. It has not been reviewed by a botanist. Conditions and plant responses vary; use the checks above to decide what applies. Read our editorial standards.
- University of Minnesota Extension: Building a rain garden
Runoff interception, utility marking, site testing and regional setback considerations.
- University of Maryland Extension hosted: Watershed Stewards Academy rain gardens manual
Exclude unsuitable groundwater, utility, slope, well and septic locations; plan safe overflow.
- UMass Extension: Rain gardens, a way to improve water quality
Drainage assessment, avoiding existing poorly drained spots and distinguishing wetland conditions.