Design a Rain Garden

Rain gardens are a sustainable way to reduce flooding and erosion, improve water quality, support wildlife and pollinators.

Rain gardens are designed to capture and absorb rainwater runoff from hard surfaces, instead of letting it flow into storm drains where it can carry pollutants to rivers and lakes.

Rain gardens include native plants with deep roots and soil to naturally filter and soak up water. A rain garden captures 30% more water than the same size area of lawn.

Photo source: Down to Earth Services

Residential Rain Garden programs

Several local governments in the Kansas City region offer programs that help cover the cost of installing a residential rain garden, and other water-wise habits. If you live in one of these cities or counties, visit the provided links to learn more about each cost‑sharing opportunity.

How to design a rain garden

Planning

Start simple by replacing turf grass and non-native beds with deep-rooted native plants near downspouts and around driveways and sidewalks to soak in water.
Evaluate the location’s sun exposure, soil type, and slope to guide planting choices.

Design

Rain gardens can be bowl-shaped to enhance their ability to catch and soak in water, or may allow water to flow down a low to moderate slope.
Rain gardens come in many shapes and sizes — these general steps can help you design a garden that will effectively process the rainwater that falls on your roof.

Tools needed

Supplies

Locate and mark your site

Start by looking at your downspouts and choose an area that is at least 10 square feet to capture some of the roof’s runoff.
Make sure the downspout water flows away from the house foundation. In narrow side yards, direct the water toward the front or back yard, where it can soak into the ground at least 10 feet away from the building.
Once you’ve chosen the spot, mark the outer edge of the rain garden using string and secure it to the ground with garden staples.

Mark outflow area

A rain garden won’t catch all the water that runs off your roof or yard, especially during big storms.

To handle extra water, choose a spot on the lowest edge of your rain garden basin where water can safely flow out. Mark this as your overflow area, and make sure it guides water downhill and away from your home or other buildings.

Test soil drainage

Dig a hole about 12 inches wide and 12 inches deep in the center of the area where you plan to build your rain garden.
Fill the hole with water and let it drain completely. Repeat this step until the soil is fully soaked. (Heavy clay soils may take several hours or even overnight.)
Refill the hole with water. Use a ruler or measuring stick to note the water level.
After 15 minutes, measure how much the water level has dropped.
Multiply that number by 4 to calculate how much water drains per hour.
Use this rate to determine whether your soil needs amendments to improve drainage, using the table below.

Drainage time	Amendments needed	Plant type
> 1/2 inch per hour	No, soil drains well	Drought tolerant
1/2 – 1/4 inches per hour	No, soil holds rainfall, but drains within 24-48 hours	Water-loving
< 1/4 inch per hour	Yes, soil drains poorly	Water-loving

Improve soil as needed

If the water in your test basin drops less than ¼ inch in an hour and the area still hasn’t fully soaked in after 24 hours, follow these steps to improve drainage:

Remove the top layer of soil

Lay a tarp or sturdy cloth next to the rain‑garden area.
Dig out the top 2 feet of soil from the basin area.
Place the removed soil on the tarp so it doesn’t mix with grass or debris.

Add a drainage layer

Fill the bottom of the hole with 1 foot of sand or small gravel. This helps water absorb faster.

Replace the loosened soil

Break up and crumble the soil you dug out so it’s loose and fluffy.
Put the loosened soil back on top of the sand/gravel until the area reaches the bottom of the basin level.

Use extra soil for shaping

Any leftover soil can be used to strengthen the edges of the basin
or build small berms (mounds) to help direct overflow water where you want it to go.

Install native plants

Select native plants that can handle both wet and dry spells and suit the sunlight conditions of your site.

Learn which native plants to choose for your rain garden.

Add mulch

Mulch with about 3 inches of compost or untreated wood mulch to help prevent erosion while plants become established.

Watering needs

For the first 3–4 weeks

Redirect the downspout away from the rain garden so new plants aren’t flooded.
Water the plants slowly by hand every other day to help them get established.

After the first month

Let rainfall do most of the work.
Check plants in the morning, especially in hot weather. If they look wilted, water them deeply once every 1–2 weeks until the plants are established.

Over time

Plants are considered established once they show new growth during the growing season—even a little counts. As the plants mature, your rain garden will absorb more rain, reduce erosion, and attract pollinators.