Maintain the Rain Garden
Maintenance of a rain garden is much the same as the maintenance of any other garden or landscape feature.
Weed Control and Watering
The first 1–2 years in a garden there is a higher need for weed control and attention to supplemental watering. Scrutinize which plants are weeds and keep them removed on a regular basis. Weeds are opportunistic and take advantage of open space. Replace any dead plants as soon as possible so that voids are not left open in the garden. Once the desired plants have established and are full grown, their foliage will effectively out-compete most weed species. Established plants may need supplemental watering especially during periods of drought. Monitor the appearance of the plants to determine if and when plants may need additional water. Avoid overwatering to keep plants healthy and conserve water.
Clean Edges
Maintain a clean edge! This can be done by adding a path, mowing and mulching the edge, etc. Clean edges are extremely important when designing a loose, natural style for a rain garden. Adding elements such as low fencing, stones, or a bench will also give the intended, maintained look to the garden.
Spring Clean-up
Pruning in a rain garden is the same as with any garden and is dependent upon the type of plants selected. Pruning of shrubs to enhance flowering and shape should be done according to the recommendations for each particular species. Deadheading of spent flowers to promote additional flowering may be done. However, keep in mind that birds depend on much of the seed produced throughout the year for food. Consider either deadheading half of the plants or not at all.
At the end of the growing season, as winter approaches, do not cut the plants to the ground. Instead, leave stems and seed heads to provide winter habitat in the form of cover and food. Remove the previous season’s dead foliage in early spring as new growth beings to emerge.
Mulch
If an organic mulch, such as bark mulch, is used, it should be applied in late fall-early winter. Note that once the plants have filled in, it may not be necessary or even feasible to try to apply mulch within the planted bed. A perimeter of mulch around the outside of the rain garden gives the garden a finished look and a clean edge. Mulch any bare areas as needed. If gravel and/or stone is used (in areas of high energy water flow), check periodically and clean out leaves, silt and other debris that has flowed into and covered it.
Fertilizing
Fertilize your rain garden sparingly, if at all. Native plants do well with few or no additional nutrient applications. If the plants have healthy green growth and bloom well, they do not need any additional fertilizer. Excess fertilizers dissolved in rainwater runoff causes water pollution. Use of organic fertilizers and compost rather than inorganic fertilizers is recommended if additional nutrients are needed. Spread a thin layer (1–2″) of compost on the soil surface in early spring and again in late fall. This can be topped with a thin layer of organic mulch if desired.
Download a Rain Garden/Bioswale Maintenance Overview [pdf]