Planting the rain garden is the fun part! Select plants that have a well-established root system. Usually one or two-year-old plants will have root systems that are beginning to circle or get matted. (Note: use only nursery-propagated plants; do not collect plants from the wild).
Make sure to have at least a rough plan for which plants will be planted where. Lay out the plants as planned one foot apart in a grid pattern, keeping them in containers if possible until they are actually planted to prevent drying out before they get in the ground.
Dig each hole twice as wide as the plant plug and deep enough to keep the crown of the young plant level with the existing grade (just as it was growing in the cell pack or container). Make sure the crown is level and then ﬁll the hole and ﬁrmly tamp around the roots to avoid air pockets.
Apply double-shredded mulch evenly over the bed approximately two inches thick, but avoid burying the crowns of the new transplants. Mulching is usually not necessary after the second growing season unless the “mulched look” is desired.
Stick plant labels next to each individual grouping. This will help identify the young native plants from non-desirable species (weeds) as you weed the garden.
As a general rule plants need one inch of water per week. Water immediately after planting and continue to water twice a week (unless rain does the job) until the plugs are established. You should not have to water your rain garden once the plants are established. Plugs can be planted anytime during the growing season as long as they get adequate water.
Weeding will be needed the ﬁrst couple of years. Remove by hand only those plants you are certain are weeds. Try to get out all the roots of the weedy plants. Weeds may not be a problem in the second season, depending on the variety and tenacity of weeds present. In the third year and beyond, the native grasses, sedges, rushes, and wildﬂowers will begin to mature and will out-compete the weeds. Weeding isolated patches might still be needed on occasion.
After each growing season, the stems and seed heads can be left for winter interest, wildlife cover and bird food. Once spring arrives and new growth is 4-6-inches tall, cut all tattered plants back. If the growth is really thick, hand-cut the largest plants and then use a string trimmer to mow the planting back to a height of six to eight inches. Dead plant material can also be removed with a string trimmer or weed whacker (scythe) and composted or disposed of as appropriate
One important maintenance problem to look out for is water standing in the garden too long. Usually you do not want standing water for more than a day. This is especially important when the depth of the water leaves young plants mostly submerged. The standing water problem should diminish as plants improve the infiltration rates as they mature. The simplest solution is to dig a small opening in the berm to let some of the water out. Replacing the soil with gravel can help stabilize the opening. This defeats some of the purpose of a rain garden but allows the plants to survive. After the first or second year, plug the opening and see if the drainage problem is resolved.