The US Environmental Protection Agency estimates 70% of the pollution in our streams, rivers, watersheds, and lakes is carried there by storm water (image courtesy: frontiergroup.org).
By: John Green- Certified Texas Expert Gardener, Orange, TX
Frankly, the name ‘Rain Garden’ is a misnomer for what it is since a ‘Rain Garden’ is nothing more than an area in the landscape where water pools after rain events and specific plant types are planted. For many of us in SETX, storm water runoff is a problem after heavy thunderstorms or from our daily rain showers which have occurred throughout the summer.
Rain fall runs off roofs, driveways, parking lots, streets, yards, and pastures (which are all primary sources of contamination) that eventually drain into municipal storm drains or in my case, pastures which drain into Cow bayou, then flowing into the Sabine river. Excessive rainfall becomes storm water runoff which captures “undesirable” contaminants as it flows from source to destination (water sheds or storm drains) such as hydrocarbons (oil & gas), chemicals, and fertilizers as it travels. The US Environmental Protection Agency estimates 70% of the pollution in our streams, rivers, water sheds, and lakes is carried there by storm water. As gardeners we can create areas within our landscapes to mitigate storm water contamination as well as be mindful of the “undesirable” contaminates we use as we cultivate our landscapes!
Creating a rain garden in clay soil presents unique challenges due to poor drainage, and the soil’s dense, compact nature but with careful planning a functional rain garden can be achieved which provides benefit to our environment. So, let’s “dig in” (pun intended)- this is a guide for how to build a rain garden in clay soil. Every garden project begins with a plan!
Rain Garden Plan
Soil test- it’s always best to understand the soil type and structure before beginning a landscape project. Contact the local County agricultural extension office for details on gathering soil samples for analysis. The cost is minimal, and the information provided is invaluable!
Soil assessment (clay soil drains slowly)- a soil drainage test is required, which involves digging a hole 12 to 18-inches deep and wide, then filling with water. If the hole drains within 24 hours, the area is suitable site.
Select site- this is an important step and the site chosen must be a low-lying area but should be away from building foundations.
Site dimension- make the rain garden about 60% of the drainage area. If amending the area reduce the size to between 20 to 30%.
Garden depth- a suggested depth of 4 to 6-inches is typical for clay soils.
Water flow- direct water into the garden and prevent overflow by building a berm for
containment.
Clay Soil Improvement
Avoid working with wet clay soil to prevent compaction, always dig when the soil is dry.
Dig a shallow basin with sloping edges, and save the soil removed to build a berm if necessary.
Enhance water filtration by allowing the bottom and side areas to remain rough surfaced.
Adding organic material improves drainage. Use a mix of sand, topsoil, and compost aiming for approximately 10% clay.
Plant Selection
Select plants that tolerate fluctuating moisture. Native plants and wildflowers are often suitable and adaptable. Many native plants are less susceptible to disease and insect problems. These are a few of the plants which can be grown successfully grown in SETX– ferns, iris, swamp milkweed, asters, black-eyed Susan, Bluestar (Amsonia), Joe Pye weed, Coneflowers, Summersweet, Daylilies, Coral Bells, Blue Wild Indigo, Viburnum, Rose of Sharon, Cardinal Flower, ornamental grasses, Hardy Hibiscus, and
Texas Star Hibiscus are but a few plants which thrive when planted in rain gardens.
Divide the garden into zones based on water levels (height)- lowest for standing water, middle for moist conditions, and upper for drier conditions.
Ensure that when plants are transplanted the root ball is untangled (break up root ball) to encourage root expansion.
Apply hardwood shredded mulch to retain moisture, suppress weeds, and aid with filtering contaminants.
Garden Maintenance
Even though it’s a ‘Rain garden’ it must be watered regularly in the first year, typically once a week until plants are established.
Check for standing water and if it persists for more than 48 hours, aeration and additional drainage will be necessary.
Weed control is important and requires that weeds be removed by hand to avoid disturbing the soil.
Replenish mulch at least twice annually, since adding a fresh layer of mulch improves soil health and suppresses weeds.
Fall or early spring pruning of perennials will help to maintain optimal plant health.
Rain gardens don’t have to be large, and gardeners can make them any size they want. Any size rain garden will help filter storm water. Many gardeners may not realize that marshes and watersheds are Nature’s rain gardens! Marsh plants filter and clean the water along with the plants stabilizing the ground below the water.
For more information on how to create a rain garden, visit: https://watersmart.tamu.edu/rain-garden/ or http://rainwaterharvesting.tamu.edu/files/2011/05/Rain-Garden-Plant-List-11-02-09.pdf.
So long for now fellow gardeners! Let’s go out and grow ourselves a greener, more sustainable
world, one ‘Rain Garden’ at a time! Gardening questions answered: jongreene57@gmail.com.
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