Rain Garden Design
Garden at a glance:
Sun-loving plants (see list below)
Plants that can survive being in standing water for 1-2 days and then be in completely dry conditions for weeks on end (NOT ponds or long-term standing water)
Also has dry plants for the dry slopes of rain gardens
Attracts huge amounts of monarchs and butterflies
This garden will plant an area from 10ft x 10ft up to 10ft x 15ft
How to design and plant:
Rain gardens are depressions in the landscape designed to be dry most of the time, allow about 3” to 12” of water to pond after a rainfall, and then soak that water completely into the ground within 24-48 hours so that the rain garden is dry again with room to take the next rainfall. They reduce stormwater runoff and reduce water pollution. Ponds are much different from rain gardens—ponds hold water forever and don’t dry up between rainfalls. These plants cannot survive in ponds or “wet spots in my yard”!
Plant the wet/dry plants in the bottom basin of the rain garden—Marsh Milkweed, Blue Wild Indigo, Blue Flag Iris, Meadow Blazing Star, Great Blue Lobelia, Prairie Loosestrife, Culver’s Root, and Fox Sedge.
Plant the remainder of the plants on the dry upper slopes away from the bottom basin
Plant the shortest flowers near the borders—Nodding Onion, Prairie Smoke, and Bradbury’s Monarda.
Most plants can be planted 12-15 inches apart, but the Orange Coneflower and Aromatic Aster spread underground so plant them 18-24 inches away from other plants, and the Blue Wild Indigo also becomes a large clump after a few years.
Materials and Supplies:
Plants - you can buy this as a pre-made garden kit or purchase the plants as pots separately. The garden kit is cheaper but the pots are larger, more mature plants.
3” of wood mulch (1 cubic yard, or 14 bags of 2 cubic foot mulch). Wood mulch reduces weeds, reduces watering to just 3-5 times the first year, and nearly doubles plant growth—well worth the extra work (a few hours) and cost (about $40 for a 10ft x 10ft area).
Paper weed-block rolls or cardboard or newspaper to put underneath the mulch. Do not use plastic!
Edging - 5” deep plastic edging or blocks.
Sticks or popsicle sticks to mark the plants. Plastic labels will break over time.
Plants needed:
Flowers:
6 Nodding Onion (Allium cernuum)
2 Marsh Milkweed (Asclepias incarnata)
1 Aromatic Aster (Aster oblongifolius)
2 Blue Wild Indigo (Baptisia australis)
3 Prairie Smoke (Geum triflorum)
3 Blue Flag Iris (Iris versicolor)
11 Meadow Blazing Star (Liatris ligulistylis)
6 Great Blue Lobelia (Lobelia siphilitica)
3 Prairie Loosestrife (Lysimachia quadriflora)
3 Bradbury's Monarda (Monarda bradburiana)
3 Prairie Phlox (Phlox pilosa)
3 Orange Coneflower (Rudbeckia fulgida)
3 Culver's Root (Veronicastrum virginicum)
Grasses and Sedges:
8 Star Sedge (Carex radiata)
9 Fox Sedge (Carex vulpinoidea)
6 Prairie Dropseed (Sporobolus heterolepis)
What to expect (A Garden Journal):
This is a great rain garden for sunny areas. It has the dual-purpose of reducing stormwater pollution and also benefiting pollinators!
In April, the Prairie Smoke will start blooming with its nodding red flowers. If you’re lucky, you’ll see a bumblebee attach itself upside-down and buzz its wings to shake the pollen out. After blooming the flowers point upwards and the seed heads look like puffs of smoke. Bradbury’s Monarda will form a short mound of beautiful purple and dark green leaves which smell like mint. It spreads slowly by underground rhizomes, or roots, after a few years. Bumblebees enjoy the pink spotted flowers in late May.
The sedges will start to re-sprout right when the snow melts. Sedges are like grasses but have triangle stems. Most are cool-season and like to grow when the weather is colder, just like lawn grasses, which is a welcome sight when so many other native plants are still dormant. Star Sedge and Parasol Sedge stay in short clumps and form seed heads in early summer.
The sprouts of Blue Wild Indigo look like asparagus shoots when they first come out of the ground. It is a legume, a nitrogen-fixer, and helps put nitrogen fertilizer back into the soil. It has deep blue flowers on tall stems but it is a very slow bloomer and might take 2-3 years to bloom and become a mature clump. In the winter, the leaves turn almost black and it looks nice in the snow.
In late May and early June, Prairie Phlox flowers are popular with small skipper butterflies. The tiny seed pods pop when they ripen, and if you stand next to them on a warm sunny day you can hear them crackling! Blue Flag Iris blooms around the same time. It has tall sword-like leaves. Native Blue Flag Iris has flowers that bloom below the tops of the leaves in the middle of the plant; non-native blue Iris flowers bloom well above the leaves.
During summer Marsh Milkweed is a very popular host plant for monarch butterflies. If you notice a monarch in your garden, watch if they land upside-down on a milkweed leaf to lay a single tiny white egg. The caterpillars often stay underneath the leaves while they are small and get more bold as they grow larger. Prairie Loosestrife is a unique wet meadow flower that has nodding pale yellow flowers. After it blooms it forms shiny maroon seed pods in the shape of little spheres.
Great Blue Lobelia blooms at the end of summer with spikes of flowers that are pollinated by bumblebees. The deep blue flowers go well next to the dark yellow flowers of Orange Coneflower. Orange Coneflower is also known as black eyed susan and is a popular garden plant. It spreads by underground rhizomes each year and forms a nice patch.
Near the end of summer, the blooms of Culver’s Root and Nodding Onion are popular with many types of bees which are important pollinators for native plants. Nodding Onion has short pink flowers, while Culver’s Root has tall white flower spikes and whorled leaves. Nodding Onion does have edible onion bulbs but they aren’t very flavorful and too much can cause stomach aches! It spreads easily by seed and the new seedlings look like little grass sprouts.
The grand finale is Meadow Blazing Star. For some reason, monarch are extremely attracted to the nectar (we call it the Monarch Magnet!). It’s truly an amazing sight. It isn’t unusual to see monarchs flying around all day, every day from mid-August to early September.
The last flower to bloom is Aromatic Aster in October. It forms a dense mound that spreads by underground rhizomes about 8 inches a year, so keep it spread out from other plants in the beginning. The light bluish-purple flowers are very important fall nectar and pollen sources for many bees and butterflies when nothing else is blooming. It can survive frosts and we’ve even seen it bloom in Minnesota in November!
Maintenance:
Weeding. The first two years are really important, so try to weed every few weeks and pull out even the tiniest weeds each time. If weeds get too big, their big roots pulls up clumps of large clumps of dirt and it wrecks the mulch layer. Watch for weedy grasses that seem to be spreading underground inches or feet at a time—these are particularly difficult weeds to keep under control (all of the grasses or sedges stay in clumps and don’t spread underground).
Watering. If you used 3 inches of wood mulch, you’ll probably only need to water twice a week for a 4-6 weeks after planting and then never again! But always be sure to watch for wilting leaves. Never water every day, and always check the soil moisture under the mulch with your finger before deciding if they need water or not. We have never needed to water a native plant garden after the first year of establishment!
Trimming. At the end of the year you can leave all of the stems over winter. Birds will continue to eat the seeds of Dotted Blazing Star and Narrow Leaf Coneflower into early winter. Bees and insect larvae overwinter in stems. The foliage provides winter interest as it sticks out of the snow. You can also choose to cut things back or mow everything down in fall or spring. Cutting things down allows more sun to reach the ground and plant crowns, warming things up faster in the spring and making things re-sprout earlier.
Mulching. If you use 3 inches of wood mulch to start and make sure you pull weeds when they are very small so their roots don’t wreck the mulch layer when pulled, you shouldn’t have to mulch again—the wood mulch will stay intact as the native plants mature and spread over the years. As the native plants get bigger, especially the grasses and sedges, their leaves will create a natural mulch layer at the end of each season.