Maintaining Your Rain Garden
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Maintaining Your Rain Garden
Illinois Master Gardener Program and RainReady
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The Illinois Master Gardener Program is a project of University of Illinois Extension. RainReady is a program of the Center for Neighborhood Technology.
About the Illinois Master Gardener Program
Master Gardeners are adults of all ages who love gardening and who have previous gardening experience.You can become a Master Gardener if:you have some knowledge or experience in gardening or landscape management (you need not be an expert),you are willing to learn about horticulture and share this knowledge with others,you are accepted into a local training program and can volunteer time conducting horticultural educational programming coordinated through your local Extension unit.
University of Illinois Extension uses trained Master Gardener volunteers to meet the constant demand for horticultural consumer information by citizens of our state.
https://web.extension.illinois.edu/mg/
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MG programs are a national educational program of land grant universities through agricultural extension. Over 3000 MGs in Illinois. Annual training programs and continuing education.
Bioswales and Rain Gardens
• Bioswale: landscape element designed to concentrate or remove silt and pollution from surface runoff water, generally from large paved areas such as roads or parking lots. They consist of a swaled drainage course with gently sloped sides (less than 6%) and filled with vegetation, compost and/or riprap.
• Raingarden: gardens that have a slight depression to help collect water and are vegetated with plants that can withstand moisture regimes ranging from flooded to dry.
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This is a cross-section of a bioswale. You can see the scale of the installation, the layers of gravel that have been installed, and the unmown, native vegetation. According to Clemson University’s Extension Division, swales can be categorized by design and planting, but in general their function is the same—to slow the flow of water following heavy rains. -Grassed swales are planted with turfgrass that is mowed. These provide a more manicured look, but have been demonstrated as less effective in slowing stormwater runoff than swales with taller plants. -Vegetated bioswales can be planted with ornamental grasses, shrubs, perennials, or a combination of these. Mulch or stone are used to protect soils in areas not covered by turfgrass. Larger stone can also be used to break up concentrated flows of water and reduce velocity. -Xeriscape, or low water use, swales are useful in areas with hot summers or dry conditions. Most bioswales are designed to be dry except just after rain events. -Wet swales function similarly to stormwater wetlands.
Cross Section of a Rain Garden
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As you can see here, the rain garden is on a smaller scale and involves less construction. It relies on plants that can tolerate high levels of variation in wet and dry conditions, a depth of 6” to 12”, appropriate soil (doesn’t have high clay content, if polluted runoff is an issue has the ability to absorb high levels of nutrients—for example, Al and Fe help soil remove phosphorus and C helps it remove N). It doesn’t have a liner because its function is to slowly release water into soil and down to the water table.
Healthy Functioning Rain Garden
General Overview of Maintenance
Check inflow and outflow regularly and clear away any debris
Check from time to time to make sure it is draining properly
Make sure a hard surface or crust hasn’t formed
Maintain 2 to 4 inches of mulch
Do not use inorganic fertilizers
Remove weeds, don’t use pesticides to control them
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Understanding how the raingarden is constructed and what its purpose is, the basics of maintenance become evident. Anything that speeds the flow of water (like erosion or an accumulation of stones or gravel on the side) or slows it down so the raingarden doesn’t empty after 24 hours interferes with the functioning of the rain garden. So do weeds like bindweed that spread under the soil surface and make it less permeable, or dandelions and clover that will crowd out your deeply rooted natives, whose root systems help convey the surface water downward.
Basic Maintenance
Water after planting and during dry spells whenever the top 4 inches is dry—especially during the first two years after establishing your rain garden
Maintain a 2 to 4 inch layer of organic mulch (ideally shredded hardwood)
Keep weeded, especially in the first two years
Remove dead plants and dead or unsightly growth; replace with healthy plants unless the dead plant had a fungus or other disease
Don’t remove plants when dormant (early Spring)
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Watering during the first two years while the plantings get established is important to ensure the raingarden will be successful. You want to either check the soil—by digging a small hole to see how moist the top 4-6 inches are—or water thoroughly twice a week, ensuring that the water goes deep. A rain gauge to measure how many inches of water the plants have received—not less than an inch—might be helpful.
Seasonal Maintenance 1
In Winter (January-February), remove trash and debris; don’t pile snow onto rain garden but don’t remove snow that has fallen there; don’t use chemical ice melts near the inflow of the rain gardenIn Spring (March-April-May), Remove dead plant parts; replace mulch if needed; thin or trim overcrowded plants
Check for erosion and excessive flooding during storms
Weed, water if dry, and replant if needed
Clear any gutters connected to the rain garden
Seasonal Maintenance 2
In Summer (June-July-August), Check for erosion and excessive flooding during storms
Weed weekly, water during periods of drought or if soil is dry below 4 inches
In Early Fall (September-October),Check for erosion and excessive flooding during storms
Weed, and water during periods of drought or if soil is dry below 4 inches
Replant if necessary
Check pH and adjust if necessary (keep pH between 8 and 5)
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You can get ph meters at garden supply stores or online, or you can do it yourself: You can test your garden soil pH with vinegar and baking soda. Collect 1 cup of soil from different parts of your garden and put 2 spoonfuls into separate containers. Add 1/2 cup of vinegar to thesoil. If it fizzes, you have alkaline soil, with a pHbetween 7 and 8. If it doesn’t fizz after doing the vinegar test, then add distilled water to the other container until 2 teaspoons of soil are muddy. Add 1/2 cup baking soda. If it fizzes you have acidic soil, most likely with a pH between 5 and 6.
Seasonal Maintenance 3
In early Winter (November-December),Replace mulch as needed
If excess fine sediment has accumulated, remove gently with a shovel without disturbing plants
Correcting Problems
• If water stands for more than 24 hours, the rain garden is not draining properly. This can be corrected by a contractor.
• If you see gullying or other signs of erosion during and after rain, adding more stones to the inflow area, or more mulch, can slow down the inflow of water.
Identify and Correct Erosion
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Note the channeling at the upper left side of this rain garden; water flow can be slowed by adding decorative rocks at the inflow. Images from the State of New Hampshire’s Soak Up the Rain NH Program, http://soaknh.org/projects/photo-gallery/
Water Should Completely Drain in 24 Hours
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Image from University of Connecticut Rain Gardens “How-To” Guide
Remove Weeds
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This is a raingarden in a schoolyard in Chicago in early June 2015, and you can see that while it is a lovely element of the school playground, it needs some serious attention. You can pick out dandelions, clover, and grass, all of which don’t belong in a raingarden.
What’s a Weed?
In Illinois, removeWhite clover
Purslane
Canadian thistle
Dandelion
Pigweed
Lambsquarters
Chickweed
Bindweed/Morning Glory
Wild carrot/Queen Anne’s Lace
Wild violet
Annual bluegrass
Crabgrass
Nutsedge
Ground ivy/Creeping Charlie
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Many of these plants are considered beneficial in other settings—white clover fixes nitrogen in soil; dandelion, lambsquarters and chickweed are edible and even used as herbal remedies; bluegrass is a sought-after lawn grass; and wild violets and Queen Anne’s Lace are ornamental. But they can interfere with the functioning of your rain garden, often because of their stubborn root systems.
White Clover
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Image from Chicago Botanic Garden, chicagobotanic.org
Purslane
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Image from Chicago Botanic Garden, chicagobotanic.org
Canadian Thistle
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Images from University of California IPM Program, http://ipm.ucanr.edu/PMG/C/W-CO-CARV-FL.001.html
Dandelion
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Image from Chicago Botanic Garden, chicagobotanic.org
Pigweed
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Image from University of California IPM Program, http://ipm.ucanr.edu/PMG/A/W-AM-ABLI-LS.002.html
Lambsquarters
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Image from Chicago Botanic Garden, chicagobotanic.org
Chickweed
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Image from rhs.org.uk
Bindweed/Wild Morning Glory
Wild Carrot/Queen Anne’s Lace
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Image from illinoiswildflowers.info
Wild Violet
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Image from Chicago Botanic Garden, chicagobotanic.org
Annual Bluegrass
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Image from University of California IPM Program, http://ipm.ucanr.edu/PMG/P/W-GM-PANN-MP.001.html Popular lawn grasses do not make soil absorbent; the rule of thumb is that the height of the top of the plant equals the depth of the roots, and lawn grasses function about like astroturf when it comes to water retention underneath—one reason lawns need such frequent watering. So obviously you don’t want them in your raingarden.
Crabgrass
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Image from Chicago Botanic Garden, chicagobotanic.org Not only a grass, but spreads below the soil surface, leading to matting and choking off the perking function of the soil.
Nutsedge
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Image from msuweeds.com
Ground Ivy/Creeping Charlie
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Image from Kansas State University
In Conclusion
• Spring is the time to renew and refresh:• Restore structure, if necessary.
• Remove weeds, preferably while soil is moist so the root systems are easier to get out.
• Pull GENTLY, trying not to leave pieces behind.
• Replant in bare patches, but be careful not to remove plants that are merely dormant.
• Restore 2-4 inches of mulch.
Resources
• https://www.dnr.illinois.gov/education/Pages/PlantListRainGarden.aspx
• https://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs142p2_011366.pdf
• http://www.irwp.org/conservation-and-restoration/green-infrastructure-and-lid/rain-gardens-3/rain-garden-how-to-2/
• http://web.extension.illinois.edu/hkmw/downloads/68238.pdf
• www.12000raingardens.org
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