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RAIN GARDEN What Is a Rain Garden?

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RAIN GARDEN What Is a Rain Garden? KANSAS CITY’S OVERFLOW CONTROL PROGRAM A RESIDENT’S REFERENCE GUIDE TO PROGRESS REPORT July 2013 CREATING A RAIN GARDEN What is a Rain Garden? Rain gardens are shallow depressions filled with native plants designed to catch and absorb stormwater runoff from roofs, streets, parking lots and other areas. Stormwater runoff can negatively impact our waterways by increasing erosion and contributing harmful pollutants picked up from yards, streets, and parking lots. Rain gardens help reduce these negative impacts and recharge the ground water by utilizing stormwater runoff as a resource rather than channeling it to storm drains which lead directly to area creeks, rivers and lakes. Rain gardens can also help keep extra stormwater out of our sewer system, which can often become too full, causing sewer overflows. Water that is caught in a rain garden either infiltrates into the ground, is taken up by plant roots, or evaporates into the air. Native plants are a good choice for rain gardens because they are adapted to our local growing conditions. They have massive root systems that keep soil from eroding, help water soak into the ground, and keep the plants alive during droughts. Native plants are also a vital component in our local ecosystem as they provide food and shelter to birds and insects including pollinators. Page | 2 at least 10 feet from the foundation depression gentle slope 6 inch berm Designing a Rain Garden Percolation Test Test your soil to make sure it has 1. Determine the size of your rain garden by estimating your roof area or driveway adequate infiltration for a rain square footage. The garden should be about one-third the size of the area garden. providing runoff. Sketch out your garden design on page 6. 1 Dig a hole twelve inches deep. 2. Choose a spot at least 10 feet away from your foundation, and downhill from 2 Fill it with water and let it drain all your home and your downspout, sump pump outlets, or other runoff source. the way. Perform a percolation test as shown in the box on the right. 3. Dig a shallow, flat-bottomed hole with gradually sloping sides. The average depth 3 Fill it with water a second time. If of a rain garden is 6” - 12”. Have a spot located in your landscape for excavated the water drains at least half an materials or build a berm on the downhill side of your rain garden. Fix your soil inch in an hour the second time with the mixture listed on the bottom left if your percolation test showed your you fill it, your soil has adequate drainage for a rain garden and soil was not draining properly. You may want to test your soil’s pH, as wildflowers amendments are not needed. grow best in soil with a pH level between 5.5 – 7.5. Before you dig, make sure to call 1-800-DIG-RITE so they can identify underground utilities that you should avoid. 4. Test the overflow pattern. Fill the excavated area with water and observe the overflow to ensure it flows away from buildings. Fix Your Soil 5. Direct your runoff into your rain garden if necessary by digging a shallow If the composition of the soil does channel or using drainpipe. not allow for proper drainage (see 6. Plant! Mix your amendments in the bottom of the garden (if you are percolation test) you may need to using them). Place the plants at the appropriate spacing, then check your fix it. Excavate to twice the desired arrangement before digging holes and planting. Evaluate the texture and color depth, then fill the bottom half with of adjacent plants and make any design adjustments. MULCH: add a 3-inch the amendment materials. You can mix layer of mulch. If you add mulch before planting, simply move it aside when materials right in your garden. digging holes, or after planting, place mulch loosely around plants. Untreated 50% sand + shredded hardwood mulch is best as it is less likely to float out of your garden, but any mulch is acceptable. 25% topsoil + Calculate Your Rain Garden Size 25% finished compost. How to figure the amount of space and number of plants you’ll need. How much water? Define your runoff area (e.g. 200 sq. ft. of roof or driveway). What size garden? Divide the runoff area by 3 to obtain the rain garden size (200 ÷ 3=66.6 or 67 sq. ft) or fit the garden to your space. How many plants? Your garden size divided by 2.25 for plants spaced 18” apart. (67 ÷ 2.25 = 29.7. Round to 30). So 30 plants are needed for the 67 sq. ft. garden in our example. Use same calculation to add a rain garden to any drainage area. Page | 3 Maintain your rain garden • Water your newly-planted rain garden during its first growing season. What About Mosquitoes? • Remove weeds regularly. • Remove any dead stems or seed heads that do not appeal to you. Stormwater runoff entering • Evaluate your rain garden each year. Fill any holes with the your rain garden should addition of other appropriate native plant species. disappear within 24-48* hours • To keep your garden looking neat, maintain its boundary by of a rain event. Mosquitoes clipping and mowing. Consider edging the rain garden with natural need at least a week of stone on the downhill side. Avoid using a raised edge treatment on standing water to complete the side where water flows into the rain garden. their life cycle. A poorly • In early spring, cut back last year’s growth from grasses and maintained bird bath or rain perennials. Leave the plants standing throughout the winter for gutter is a more likely breeding visual interest. Many native grasses look attractive during this time ground. of year. • Do not apply lawn fertilizers too close to your rain garden. When *If your rain garden native plants are fertilized, especially with nitrogen, they tend to is not draining in 48 grow too tall to hold themselves upright. Additionally, fertilizing hours, you may need to fix your soil. See can stimulate weed growth and create competition for the native page 3 for more plants. information. Page | 4 Rain Garden Plant Characteristics Palm Sedge (12-24”) Gray’s Sedge (24-36”) Soft Rush (24-36”) Little Bluestem (24-48”) Beakgrain (12-24”) Switchgrass (36-60”) __ __ __ __ __ __ 60 60 60 60 60 60 __ __ __ __ __ __ 48 48 48 48 48 48 __ __ __ __ __ __ 36 36 36 36 36 36 __ __ __ __ __ __ INCHES 24 24 24 24 24 24 __ __ __ __ __ __ 12 12 12 12 12 12 ER JA ECEMB NUARY D Spi land Phlo hio derw od x - O o o 3 rt W - ER 2 FE B ing Blu B hin est M n Ground S ar R de se - U E ol l T 4 A r V G a s O - a d i R s t e 1 a s en N Ph ic can hi Y r t o lo a ia x div ountain r M M i e n sh B d t ar la A z n M in e g m S l - e S 3 S so s n t i e s 1 a nia ustr - ill c u r io t o va bo 2 m 1 den Ale l u o xa i O G n M l - d o e Conefl f 5 C e o r pl w i s A ur er P u T n P yc te R O - n a L m 1 n u i C t hem a B 1 tr i ta H s spica 16 E arden P G h R - lo 15 4 x 1 E a re c h Zizia au in ea a ur atic Ast cea purp om er Ar - e Flag I Blu ris 6 1 - s 6 y terfl Mil u a t k i w t u l a B e ck-Ey l e o la ed P u - d f B h c i S lo i S 0 - u x pan 16 1 g 5 s n a E 1 n 15 S lo P y ob mp T 14 hyotrichum 1 E A L a I s I c M 13 ri i c s n v gi l ir 2 e R pi a ove Bea a s l r B 12 s tubero R xg dt P e Po u a Fo on l p d E 11 rp py d gi - g A u M be ul u R P ckia f e - al 7 9 lo w f Coreo lea psi e s c n 1 a L 2 - s 14 C i 8 P l 13 a e ita 3 l n g l s i i t e d This page shows r mon 4 The bloom 12 h a t o a A e t a a 5 what the native 11 involucr l times indicated U o 10 e 6 c G n Y rain garden plants 9 C a 7 are typical for o s l A U r eopsi 8 suggested in this S M plants in the Kansas T handout will look like over City region. Actual bloom 12 5 11 6 10 7 time. Some plants will need a 9 8 9 8 times will depend on the 10 year or two before they flower.
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