Folly River Park rain garden installed during the 2023 Master Rain Gardener certification course.
Samantha Porzelt, ©2023, Clemson Extension
Rain gardens are shallow depression gardens designed and located to receive water runoff from a roof, driveway, or lawn. They work with nature to collect, filter and infiltrate runoff, while showcasing a variety of colorful and adaptable plants. See HGIC 1864, Rain Garden Plants: Introduction for additional information on rain gardens.
While rain gardens and native plant landscaping are often considered low maintenance once plants are established, just like a regular garden, they are not completely maintenance-free. To keep a rain garden functioning year after year, it is important to have a maintenance plan. Consider including the following actions when developing your rain garden maintenance plan.
Hand water rain garden plants for the first couple of weeks after planting and during prolonged periods without rain.
Photo credit: Mary Martinich, 2022. Seamon Whiteside
Inspection
It is a good idea to visually inspect your rain garden several times a year, particularly at the end of the growing season, and after large storms or prolonged periods of drought. Look for weeds or undesirable volunteer plants that may have popped up since the rain garden was originally planted. Check inlets and outlets to ensure there are no blockages or significant erosion. Look for signs of erosion in the surrounding landscape and make necessary repairs to prevent sediment from entering the rain garden. Inspect your rain garden for standing water that has not percolated into the ground. If standing water is present longer than 36 hours after a typical rain event, the soil may be compacted. If the rain garden soil becomes compacted, a pitchfork or rake can be used to loosen the soil or break up the surface layer to allow water to better infiltrate and increase aeration. It is also a good idea to check your gutters for clogs if the rain garden is receiving water from a downspout. Ensure adequate mulch depth of approximately three inches throughout the garden, and if a berm exists, ensure that it is still intact.
Irrigation
Established rain gardens will need very little irrigation, but when the plants are first installed, they will need some assistance to thrive. Initially, water the plants every other day for the first two weeks. If planting occurs in the summer, daily watering for longer than two weeks may be necessary. Once the plants have settled into their new home, reduce watering to an as-needed basis. Rain garden plants are selected for their tolerance to both wet and dry conditions, so established plants may only need supplemental irrigation during long periods without rain. Check on rain garden plants weekly to assess signs of drought stress. Installing a rain gauge in or near a rain garden is an easy way to monitor rainfall. Ideally, rain gardens need around one inch of rain per week.
Plant Management
The purpose of a rain garden is to divert stormwater runoff from entering natural waterways, reduce the load on the local stormwater infrastructure, and manage flooding issues. Stormwater runoff often transports nutrients, such as nitrogen and phosphorus, from the adjacent landscape into the rain garden. These nutrients can serve as fertilizer for rain garden plants; thus, rain gardens should not receive additional fertilizer.
Prune, thin, or remove plants in your rain garden to avoid overcrowding and competition for resources.
Regular pruning of your rain garden plants promotes healthy growth, encourages more blooms, and maintains plants at a desired size. When plants go dormant in the winter, consider leaving bare stems for pollinators and other wildlife. As temperatures warm back up in early spring, prune last year’s bare stems to 6-12” above the ground.
Prune, thin, or remove plants in your rain garden to avoid overcrowding and competition for resources.
Samantha Porzelt, ©2022, Clemson Extension
Replenish mulch once or twice a year to maintain a 3-inch layer.
Mallory Maher, ©2023, Clemson Extension
If and when plants die, reassess the conditions to determine if other species are better suited to the rain garden. Plants that thrive may eventually need to be thinned or selectively removed to avoid overcrowding and competition for resources.
Hand-pull weeds as needed to give your target plants the necessary space, light, and water needed to thrive. Cedar mulch should be added to the rain garden once or twice a year, as needed, to maintain a depth of three inches. Adding a stake with a three-inch mark indicated is an easy way to keep track of the mulch depth. Mulch will assist with preventing weed growth, regulating soil temperature, and maintaining adequate soil moisture.
Debris
Regularly remove debris, such as litter or leaves, that may block the inlet or overflow. This will allow water to flow as designed throughout the rain garden. If debris or sediment accumulates and the rain garden is no longer a depression, identify the source of sediment, remove the debris with a rake or shovel to return to the desired shape and depth, and repair the erosion source.
Assess for damage around the berm and reshape if necessary. Inspect inlets and outlets for debris accumulation and dispose of it away from the rain garden. Inlets and outlets may need reshaping over time. To prevent future erosion, river rock can be placed on top of nonwoven geotextile fabric that is pinned into the ground.
For more information on rain gardens, visit the Clemson Extension Carolina Rain Garden Initiative website.
Originally published 02/24
