Plants in the rain garden will be more susceptible to stress when they are young, and need to be watered regularly until they are established. This usually takes one or two growing seasons. After the plants are established, you should not have to water them except during prolonged dry periods.
Even when your rain garden is fully established, it may need to be watered during dry periods. Simulate a rain event by filling the garden with about an inch of water every couple of weeks during long dry periods. This will help the water soak deeply into the ground. If you water with a sprinkler, set some containers around the garden. When the containers fill with about an inch of water, your garden has received enough water.
Weeding and Pruning
Pulling weeds is important to reduce competition for space, light, and water. Most weeds are pioneer species, which means they grow very quickly and fill open spaces, crowding out desirable plants. Remove only those plants you are certain are weeds. Weeds will become less prevalent in the garden over time as the native wildflowers, grasses, and sedges you've planted begin to mature and out-compete the weeds. Rain garden plants may be pruned or thinned to maintain a more manicured look.
Dead vegetation and debris should be removed from the garden from time to time. Vegetation should be cut back in the early spring. Keeping seedheads on during the winter will provide food for songbirds and shelter for wildlife. In the spring, cut back all dead stalks before new growth begins. If the plants are very dense, you may want to mow the garden back to a height of about 6 inches.
Mulching will help protect your garden's plants and reduce weed growth. Each spring the rain garden should be mulched with 3 inches of double-shredded hardwood mulch. Chipped bark is less desirable, as it tends to float when the garden fills with water. Some plants are dormant until late spring, so when mulching be careful not to bury the plant crown. The need to mulch each year will diminish over time as the plants mature and fill exposed soil surfaces.
If your rain garden has been in place for awhile, you may need to divide some of the plants. Dividing plants can help thin out the garden. If the plants have spread out so that there is no new growth in the center, dividing will help the plants look less "leggy" and more dense. When you divide your plants, you can give sections of the plant away to friends or neighbors, or you can plant pieces in other areas of your yard -- or in a new rain garden! Click here for step-by-step instructions for dividing plants.