Before You Start

garden sloping away from house

Factors Before You Get Started

These up-front considerations will ensure a successful rain garden, rather than an eyesore!

Location and Slope

Is your desired location:
  • Near a house
  • Near a water source
  • Below the downslope of a lawn
  • Along a sidewalk or road
  • On top of underground utilities (Hint: No way!)
  • Though native plants can still be planted on a hill, don’t expect to collect water when the slope is greater than 12%.
  • But that doesn’t mean native plants can’t be used to prevent erosion. Click here to learn more.

Make sure the rain garden is downslope from the house so water doesn’t run into the basement (see picture).


  • A larger area draining to the garden means the garden should be larger to absorb all the water (see the UWEX website for detailed size calculations).
  • The garden should be 1/3 of the size of the area draining to it, but the garden can be up to 30% smaller and still catch 90% of the water draining to it.
  • Ultimately, use the space you have available and make the garden deeper to create a garden with larger volume.
  • If your site requires a large rain garden and the rain water for the gardens is collected in rain barrels, remember this: there might not be enough water pressure to use hoses to get water to the farthest reaches of the garden (see picture at left).
  • A property boundary (red line) and an underground utility (blue line) limited the size of this Duluth, MN rain garden in a residential yard, yet it is thriving.



  • All rain gardens are saucer-shaped, though the rim of the bowl can have a square, round, or kidney bean outline.
  • To fit a rain garden into your landscaping, consider creating a rain garden as a border off to one side rather than as a big bowl plopped in the middle of your yard.
  • A distinct clean line between lawn and rain garden will give the garden a finished look, and will prevent the rain garden from looking unkempt and weedy. Use garden edging or a path to create a border.
  • Before digging, lay landscape fabric on the rain garden site for 3 months to a year. Not only does it kill the grass without herbicide, it helps to determine the size, shape, and location of the rain garden.
  • The garden pictured is lined with rocks to provide a clean edge.


Soil Type

  • Clay soil may need to be amended to aid drainage, whereas sandy soil will drain well.
  • If a sandy rain garden drains too quickly, the garden can be completely lined with a layer of clay to keep the garden moist for plants.
  • Get to know your soil! Test your soil or do a perc test. Do not make the mistake we did: we assumed we had clay soil when really we have fast-draining fill. That makes our gardens dry up quickly.
  • It always helps to till the soil after digging to aid infiltration. And take care not to drive heavy equipment into the garden!
  • Digging out a clay-filled garden is hard work! Bring your friends!

Soil Type

Preparing the Rain Garden Bed

A sandy rain garden can be deep and small, while a clayey rain garden should be shallow and large.
A rain garden is typically between 3 and 8 inches deep.
The garden can be dug by hand or with heavy equipment (but don’t compact the soil by letting heavy equipment drive across the garden bed!).
A sod cutter is also helpful for tenacious sod grass.
When digging, make sure the bottom of the rain garden is flat so the water spreads evenly in the bottom of the rain garden.
Call Diggers Hotline before you dig!

Preparing the Rain Garden Bed.png


The price of a garden is determined by how much work you do yourself, as well as whether you decide to use seeds, seedlings, or to transplant mature plants. If you do the work but purchase plants, cost is about $3 to $5 per square foot. Cost of landscape consultants in Wisconsin is about $10 to $15 per square foot. Includes design, construction, plants, and planting. A 300 sq ft rain garden costs between $1,000 and $4,500.

Seeds were collected from existing native plants in the fall, grown indoors in flats, and planted in the pictured garden the following spring. The only costs incurred for this garden were for mulch, compost, and shovels.

Yellow flower

Time of year

In the northern Midwest, planting should occur between May and September. Planting in June may yield flowering plants in August of the first year!


  • There shouldn’t be any if the garden is properly sited and designed. Rain gardens should drain in no more than five days, though a garden that drains in 48 hours is ideal.
  • Mosquitoes have a 7 to 12 day life cycle from egg to adult.
  • Mosquitoes that carry most diseases don’t live in ponds. They prefer small amounts of standing water such as holes in trees, old tires, or birdbaths.