Rain gardens in Pennsylvania: where they work, how big, and who helps pay

Updated November 10, 2026 · KeystoneProGuide editorial team

What is a rain garden?

A shallow, planted basin that catches runoff and lets it soak in. Penn State Extension describes rain gardens as landscape features designed to capture stormwater from downspouts, driveways and other surfaces so it absorbs back into the ground. The EPA adds that, planted with grasses and flowering perennials, a rain garden can be a cost effective way to reduce runoff, can help filter pollutants and gives food and shelter to butterflies and birds. More complex versions, with drainage systems and amended soils, are often called bioretention.

The reason local agencies promote them is runoff. The Montgomery County Conservation District calls stormwater runoff pollution the greatest challenge to water resources, and says a rain garden provides a ponding area so runoff infiltrates slowly instead of reaching the storm sewer all at once.

Where should a rain garden go?

Penn State's siting rules are specific, and they are the part most worth getting right.

• Watch the yard in the rain. See where water flows from the roof, driveway or a compacted lawn.
• Find a low, flat spot that collects water but is not permanently waterlogged.
• Stay at least 10 feet from the foundation, so the garden does not create basement water problems.
• Avoid septic tanks, leach fields, drinking water wells, tree roots, waterlogged ground and utilities.
• Keep to gentle ground. Penn State says slopes steeper than 10% are not ideal.
• Check local rules first. Penn State advises asking your municipality about stormwater rules and plant height ordinances that may affect the design.

How do you know the soil will drain?

Test it. Soil type decides how fast water soaks in: Penn State gives about 2.5 inches an hour for sandy soil, half an inch for silty soil and a third of an inch for clay. Its percolation test is simple: dig several holes a foot deep and a foot wide where you want the garden, fill them with water and time the drainage. If it takes more than 24 hours to drain, Penn State says to consider another site.

If a landscaper proposes a rain garden, ask whether it has run this test on your site, and what the result was, before any digging starts.

How big should it be?

Penn State says a rain garden is usually 10 to 20% of the size of the hard surface draining into it, varying with the soil and the depth of the garden. It works through an example: a roof section 50 feet by 12.5 feet, or 625 square feet, sheds about 52 cubic feet of water in a one-inch storm, so a garden with a six-inch ponding depth needs to be about 104 square feet. If that does not fit, the depth, shape or location can change.

What are its parts?

Penn State describes three: an inlet, often lined with rock to slow the water coming in; a low berm with gentle slopes around a shallow basin; and an erosion-resistant outlet, also often rock-lined, for overflow. Before anyone digs, Pennsylvania 811 must be called; Penn State notes that the service is free to homeowners, and a hired contractor must make its own call.

What should you plant?

Native plants suited to the spot. Penn State says to watch the new garden after a rain and put moisture-loving plants where water stands longest, choosing natives that match the soil and sun. The Department of Conservation and Natural Resources says native plants are adapted to local conditions, persist through frost and drought, support pollinators and birds and, once established, need little else. The Montgomery County Conservation District links a native plant list for rain gardens from its homeowner page.

Will Philadelphia help pay for one?

Yes. The city's Rain Check program offers residents a free rain barrel, or a downspout planter, rain garden or porous paving installed at a reduced price. The Water Department says the program is open across the whole city and that everyone who takes part must first attend a workshop. In 2016 the department recruited contractors for the program and said they might be landscapers, hardscapers or general home contractors.

Be clear about one limit. The Water Department says stormwater credits are not available for homes, and that a rain garden or rain barrel will not reduce a residential customer's monthly stormwater charge.

Do other counties encourage them?

Through their stormwater rules and advice. The Chester County Planning Commission says new stormwater design guidance recommends green practices, rain gardens among them, wherever possible, and the county's municipalities enforce a countywide stormwater ordinance. The Montgomery County Conservation District publishes design templates for a row home and a single home rain garden.

Who builds one?

You can, following Penn State's method, or a landscaper can. If the job includes a drainage system, the Attorney General says landscapers placing drainage systems at a private home must register as home improvement contractors. For bigger drainage problems, see the drainage and grading guide, and for choosing what goes in it, native and invasive plants. Local businesses are on the landscapers directory page.

Sources

1. How to Make a Rain Garden, Penn State Extension
2. Soak Up the Rain: Rain Gardens, U.S. Environmental Protection Agency
3. Rain Gardens and Barrels, Montgomery County Conservation District
4. eTools: Stormwater Best Management Practices, Chester County Planning Commission
5. Rain Check, City of Philadelphia
6. RainCheck Goes Citywide, Philadelphia Water Department
7. Residential Stormwater Charge, Philadelphia Water Department
8. Calling landscapers and home contractors! Join our Rain Check Team, Philadelphia Water Department
9. FAQs Homeowners, Pennsylvania One Call System
10. Landscaping with Native Plants, Pennsylvania Department of Conservation and Natural Resources
11. Frequently Asked Questions: Home Improvement Contractor Registration, Pennsylvania Office of Attorney General