Rain Gardens: Practical and Beautiful

Rudbeckia hirta, commonly called black-eyed Susan

When the rain comes lately, it pours down hard, leaving trails in its wake and amazing us with how much it collects. How we manage rain can vary, but a rain garden is nature’s truest solution. With a little work on the install, you can be left with a treasure that will delight you, nurture the earth, and manage your rainfall without you having to think much about it.

There are a plethora of options and questions when you explore keeping water on site. How do you begin? What do you want the water-moving entity to look like? Do you want plants? Would you like to see rocks? Big ones or small ones? How much water should you prepare for? What happens if it doesn’t rain? What’s the upkeep? Rain gardens can be broken down pretty simply though, and can be installed easily enough to manage your watershed.

It’s extremely important to first look up before looking down. Consider your roof layout and downspout positioning. How much of the roof feeds your downspout? A quick measurement of the catchment area will help determine the depth, size, and positioning of the retention area. Minimally, stay four feet from any foundation and three feet from any sidewalk. Call Diggers Hotline (811) to pinpoint gas utilities and electrical lines. Determining where other utilities, underground electrical wires, internet cables, plumbing, phone, etc., are located is equally important. Other considerations should include nearby tree roots, plantings, yard features, and pathways.

When the rough position and amount of water the rain garden must move has been determined, shape is next. Recessed-ditch retention or rock-filled drainage? You can plant a shallow, round ditch with a smooth bottom and water-drinking plants, or fill a deeper, more compact-sized retention with varying sized rocks—small on the bottom and large on the top—creating a level surface. You can maintain plants or have rocked drainage that feeds existing lawn, trees, and gardens.

These decisions lump together because they take you different directions. One option is a lush, rich garden filled with native plants and trees, bumbling with beneficial insects of all kinds, while the other is lovely, simple, and serene, yet more geological looking, all while managing rainfall with a bit less upkeep.

Author’s favorite rain garden plants: Lobelia cardinalis, Red cardinal flower Schizachyrium Scoparium, Little blue stem Monarda Media, Bergamot Eupatorium fistulosum, Joe-Pye weed Asclepias incarnata, Swamp milkweed Vernonia noveboracensis, Ironweed Phlox Maculate, Meadow Phlox Iris versicolor, Blue Flag Iris Thalictrum Pubescens, Meadow Rue Geranium Maculatum, Wild geranium, Anything Carex variety, Sedge Sambucus canadensis, Elderberry Cornus varieties, Dogwood Lindera benzoin, Spicebush Betula negra, River Birch, Celtis occidentalis, Hackberry

Incorporating a sunken corrugated or PVC pipe is often a needed component for the nonplanted varieties to adequately move the water. Rain garden plants work double duty, as they not only look pretty and promote healthy insect life, but also drink tons of water. Without these thirsty friends, you’ll need to consider the method the water travels underground and away from your building, which is largely reliant on how much water you’re dealing with.

The best shapes for rain gardens resemble large, wide cereal bowls with large edges, a designed spill side, and deeper basin ends or tributaries to ease overflow. These bowl irregularities allow additional collection and feed auxiliary plants or areas while giving you more control over where any extra water would flow. This is where the PVC piping comes into play.

It’s extremely important to maintain an outwardly or downward path to the overall bottom of the retention area. Any tributaries should maintain this slope with the annex areas dug to feed out to them or be slightly deeper to allow for another pooling area. These shapes and outlets often operate best when not perfectly circular, but parabolic, almost octopus looking. Multiple pooling areas can be very beneficial if you have a lot of water or a larger planting zone and want to be sure you’re distributing the moisture more evenly downstream. Be sure the downward slope is in overall effect.

Personally, and for safety reasons, I prefer to keep all ground leveled or raised in appearance, though trenches may run deep. I choose to fill retentions first with a layer of sand, several inches of clear stone or pea gravel or both, and then cover with either pea gravel for foot traffic or large stone to create a feature that’s prominent in all four seasons. These rock-filled trenches, sometimes called French drains, often stay wet much longer than the ground, thaw earlier, and reduce insect larvae capability. I usually select a few key stones to help break the flow from the downspout wherever it seems appropriate. Checking things in a downpour so you can adjust as needed is wise.

If you do not rock your garden, be sure slopes descend gradually, are shallower than rock rain gardens, packed well at the base. If you fill it, the edges may be sharper and more jagged looking, and you can create a deep basin. The planting area surrounding or filling these retentions should be varieties specific to rain gardens. There are many resources, but pay attention to native varieties, sun preferences, and salt tolerances if the garden will be edging sidewalks or driveways. Many trees and shrubs can drink just as much water and bring in greatly differing habitats and finished looks.

General upkeep includes keeping waterways flowing and clear of debris. Adjust flow blockers if too much force is damaging or disrupting plants or soil. Plant maintenance is minimal for perennial beds. Once established—three to four years—your rain garden perennials should have deep enough roots that they can withstand several weeks of dry weather and be relatively unaffected. Long-term droughts, though, may cause some species to go dormant, sometimes rendering them dead.

Midwest rainfalls seem to be increasing, as does our need to compensate. A rain garden can be both a practical and beautiful solution for your home.

Karina Mae is the designer and team leader at Garden Search & Rescue.

Garden Search & Rescue
Madison, WI

Formula for measuring amount of flow and size of raingarden:
Width X Length of catchment area (roof) /
the number of downspouts multiplied by
the amount of rainfall = gallons of rain
550 gallons of water for every
1,000 square feet per inch of rain
1 year average: Square feet /
1,000 X 550 X annual rainfall
50 square feet (5 X 10, 7 X 7, etc.)
of planted garden can drink 200
gallons of water per inch of rainfall.