COLUMBUS, Ohio – Despite opening in late January, the CENTS show’s first day felt more like March. Intermittent rain showers and temperatures in the mid-50s greeted attendees at the Ohio Nursery and Landscape Association’s annual tradeshow and Ohio State University’s Short Course.
This year marked the first time attendees had access to a full-fledged business education track, with courses on accounting, taxes and other topics that moved away from the show’s traditional foundation of horticulture.
The show also highlighted green and sustainable practices. One session, led by Eric Sauer, ASLA and principal at CYP Studios, Centerville, Ohio, focused on the design of rain gardens. Ohio – and much of the Midwest – saw one of its rainiest years on record in 2011, and many landscapers and designers had to figure out what to do with all that water.
STORMWATER STRUCTURES. Sauer said that, whatever you call them -- bioretention areas, detention/retention basins, rain gardens or swales – stormwater structures all do the same thing: capture and clean water.
And where the traditional approach to stormwater was to get it off site as fast as possible, contemporary designs aim to hold onto water – for as long as 48 hours – to avoid overwhelming natural and manmade infrastructure.
“How do we clean the water, how do we touch the water before it gets into a pipe or natural stream?” Sauer says. “How do we get it to slow down or hold it on site?”
And these structures do more than just hold runoff. They also improve water quality, improve drainage for a property, offer a place to store snow in the winter and attract beneficial wildlife.
DESIGN CONSDIERATIONS. Sauer stressed that a rain garden filled with native plantings does not have to look like a wild, unkempt prairie. In fact, the best designs are the ones that don’t look like a rain garden at all.
“That’s a perfectly acceptable style, but a lot of people don’t like that look,” Sauer says.
His other main point to attendees was that a rain garden isn’t designed much differently than any other landscape installation. The same factors – drainage, soil pH, solar exposure, planned use – all are still relevant.
“You can’t go dig a hole, plant some plants and except things to be successful,” he says. “Trial and error is not a good way to do this. You have to give it some thought.”
Here are a few questions to ask when designing a rain garden:
- What’s the drainage area the system needs to handle? Is it a downspout, or a parking lot or entire subdivision? How much water are you going to get? Try to design your system to handle the largest storm your area gets in an average year – anything larger becomes cost prohibitive.
- What’s the soil like? Are you using native soils, or imported? What the garden sits in will determine your plant palate.
- Where is the system installed? “Most of our failures that we see are when these are brand new. The root systems haven’t taken hold and you get a big storm,” Sauer says. “You’re dealing with water that the system can handle after a year, but how do we handle that until the system is established?” Use core mats, erosion control blankets or temporary silt fences.
- What’s the salt exposure? If you’re building near roadsides, or parking lots, you’ll need to take this into consideration. The right plants can tolerate high exposure to salt.
MAINTENANCE CONSIDERATIONS. Just as the design of rain gardens follows traditional principles, so too does their maintenance. You have to cut back growth in the spring, remove debris and mulch. Areas to watch include the plants’ absorption of chemicals used on the property. Plants used in these systems are designed to suck up a lot of water, and they’ll take up anything else, too.
Also, the systems need a bit more attention after their initial installation. Topsoil erosion and plant establishment are very important to make sure the system takes root successfully.
“Erosion control is critically important on all of these,” Sauer says.
The author is editor and associate publisher of Lawn & Landscape magazine. Email him at firstname.lastname@example.org.
Eric Sauer, ASLA and principal at CYP Studios, Centerville, Ohio, gave the following list of trees, shrubs and perennials that perform well in rain gardens.
- Swamp White Oak – very tolerant street tree, rough at first like ginkgos, but become very attractive, tolerant of moist and dry conditions, do have acorns
- Bald Cypress – not for pocket rain gardens, but an overall large scale development-wide system, this tree is a beautiful tree, can grow standing in water, turns red in the fall
- River Birch – they don’t like to dry out, will drop leaves in the summer
- Sycamore – does fruit, but the bark texture as it ages is very attractive. Works as an urban tree, and is underused
- Black Gum – slow growing, hard to transplant and hard to get big specimens, good especially in parking lots, great red color in the fall
Small trees and large shrubs
- Sweetbay Magnolia – flowers off an on in summer
- Fringe Tree –
- Red Bud –
- Pagoda Dogwood – not everything has to be native. It can be adaptive.
- Serviceberry – delicious fruit
- Witch Hazel – almost blooming right now, great shrub
- Chokeberry – bright red fruit in the fall, tolerant of wet feet
- Winterberry – same thing
- Virginia Sweetspire itea – not happy dry, likes moisture to perform
- Red Twig Dogwood
- Arrowwood Viburnum – blue muffin doesn’t mature so large (5-6 feet), white flower in summer, blue fruit in fall, full shade to full sun, tolerate from wet to dry
- Rush (juncus spp.) – good seed heads, 12-36 inches in height, semi emergent on the side of a pond
- Switchgrass (Panicum spp.) – make a monoculture stand in grass prairies, three feet tall, softer with a blonde color in the fall, like wet feet, it is aggressive so be careful
- Bulrush (Scirpus spp.) – 12-18 to a great 6-7 feet tall, woody stems in some cases, becoming more common in perennial nurseries
- Sedge (Carex spp.) – thrive in full shade, interesting color in a woodland environment
- Iris (Siberian and Flags) – like an ornamental grass with a bloom in summertime, flag leaves can go 36 inches and be aggressive in wet environment
- Daylily – how can you go wrong? Know your client
- Liatris – drier growing, but a magnificent plant that attracts wildlife
- Milkweed (asclepias) – great butterfly attractor
- Coreopsis (tall and full moon) –
- Joe Pye Weed –
- Coneflower (rudbeckia)
- Cardinal flower (lobelia) – love wet feet, bright red color
- Ferns (royal and cinnamon) – can do rain gardens in the woods, work with the shade that you’ve got
Plants not to use
- Invasive species – check with your state Department of Natural Resources for its noxious weed list. In Ohio, those include cattails, purple loosestrife, burning bush and ornamental pear.
- Plants with aggressive root systems (like willows)
- Dry-loving plants (Taxus spp., sedum)