Vertical gardens take many forms, and a vertical rain garden incorporates the concept of growing plants upright to contribute to stormwater management. Rain gardens work to slow stormwater and filter pollutants before it returns to the water table. The rain irrigates the plants, which tolerate both wet and dry situations with fluctuating conditions.

Growing vertically includes trellises, arbors, and obelisks. It may incorporate a facade or fences and steep terracing. It can also be a living wall. All of these take advantage of untapped growing space.

For vertical rain garden setups, choosing the right site, plants, support structure, and mode of stormwater capture are the essential elements. By design, they offer diversity, ecological services, and boost aesthetics.

Vertical Rain Garden Elements

Take advantage of the way water moves around your garden.

Vertical rain gardens can solve challenging garden problems. Beneath downspouts, along slopes, or in low points, they take plant growth upright while slowing water flow to reduce runoff and boost infiltration.

Raise a low-lying spot with vertical elements and structural plants for interest. Enrich garden diversity and wildlife resources for forage and shelter with the specialized landscapes.

Rain gardens are typically intended to drain within 24 hours and up to 48 hours. They’ll experience moist to dry soils in the interim, depending on climate and soil composition.

Location

Choose a spot that will capture the greatest amount of water.

Rain gardens are depressed areas that absorb rainfall, channel the flow, and filter pollutants. Situate vertical configurations where they’ll best be able to capture the greatest amount, or provide a solution where runoff is an issue.

Near a downspout or beneath a gutter, where modifications can capture the stormwater for irrigation, harness the rainfall for garden use. Installing rain gardens near storm drains and ponds improves water quality before it enters waterways. Areas of natural pooling become easily adapted sites.

To capture rainwater and direct it to the vertical rain garden, use a downspout extender to direct the flow away from the foundation. Opt for a cistern or barrel to store water for irrigation, directing overflow to the rain garden.

Sizing the Garden

Adjust the size based on your available garden space.

By design, rain gardens are meant to slow flow from impervious surfaces like roofs, walkways, driveways, and even turf, depending on proximity and direction of the runoff. The retention area may only capture a portion of your site’s stormwater, depending on the area available. Based on your creative configuration, the vertical components will likely be only part of the rain garden plantings.

Factors to consider in garden sizing include available space, impervious surface area, and soil type. A useful calculation for sizing is to approximate the square footage of the area from which the garden will catch stormwater (length times width, added together if combining multiple surfaces). 

Then, account for soil type. For sandy, well-draining soils, create the garden at 20% of the total impervious square footage calculated. For loams or heavier compositions, use at least 30% of the total area calculation as the garden’s size.

The garden can comprise an already low area from pooling or form a newly created depression. Depth should be between four and eight inches.

Plants

Pick plants that tolerate more moisture than usual.

Plants for rain gardens must be adaptable and able to tolerate wet and dry spells. Plan to provide supplemental water as new transplants establish if there’s a lack of rain. Group those with similar growing conditions based on sun exposure.

The lowest part of the vertical rain garden remains saturated the longest as it drains from the top. Situate specimens that tolerate more moisture and extended “wet feet” in the lower levels. Upper levels should grow well in drier situations, as these dry out more quickly as water flows and with exposure. In both cases, plants must withstand periods of moisture and dryness.

Native plants are exceptionally durable and adaptable when it comes to localized moisture and rainfall or drought. We often think of a dense coverage of perennials (which are beneficial), but adding those with vertical interest also increases diversity. Tall, structural trees, shrubs, and perennials round out low zones.

North American native plants with upright structure and rain garden adaptability:

• American beautyberry
• Bald cypress
• Buttonbush
• Cardinal flower
• Fringetree
• Iris
• Joe Pye Weed
• Liatris
• Oakleaf hydrangea
• Red maple
• Red twig dogwood
• Rose mallow
• Sweetbay magnolia
• Switchgrass
• Winterberry

Soils

Amend soils that don’t drain quickly.

Rain garden soils need to be well-draining. Whether pockets in a plant wall or a tiered in-ground planting along a slope, soils should allow water to flow and drain. While plants withstand periods of wet soil, they won’t thrive in prolonged standing water.

Rain garden soils incorporate soil or potting mix (depending on the vertical configuration), compost, and a mulch layer to aid in filtration, aeration, and moisture retention between rains.

Growing Structures

Use trellises or fences to support climbing plants.

Flowering vines trained to an upright structure add dimension, multi-season interest, and pollinator resources. Long-lived perennial vines make a recurring show of color and add visual lift to low-lying areas. For a vertical rain garden, trellises, arbors, and tripods take the display upward. Many also run along a fence, climb a tree trunk, or trail along a slope. 

While vines have good root systems for soaking up stormwater, filling with groundcovers or other perennials beneath ensures full coverage for the best absorption and pollutant filtration.

Vining natives for vertical rain gardens:

• American wisteria
• Carolina jessamine
• Coral honeysuckle
• Climbing hydrangea
• Crossvine
• Trumpet creeper
• Virgin’s bower

Living Walls

Plant walls dry out quicker than other setups.

A living wall adds depth and layering to outdoor spaces, offering privacy and a tranquil atmosphere. They expand the growing area in small spaces and walled gardens. They also offer a unique opportunity to utilize rainwater.

Plant walls are diverse in structure, material, plantings, and irrigation. From hanging planters to modular panels, irrigation (and its runoff) can be one of the management challenges.

Like containers, living walls dry out more quickly than in-ground plantings and need watering more frequently. Positioning them on a fence or open wall provides access to natural moisture. Those under an overhang or cover need supplemental irrigation.

To utilize a living wall as a vertical rain garden, capture rain in a cistern or barrel setup. Equip it to water the wall, whether through a pump for hose-watering or drip irrigation.

Supplemental hand watering (access to water) may be useful if your climate is prone to times of lean rainfall for refilling the reserve. Rely on quality, well-draining potting mixes to support living wall plantings. 

Raised Beds

Try placing a raised bed underneath a downsprout.

A strategically placed, deep raised bed adds vertical rain garden interest. With the proper drainage in place, the elevated plants, roots, and soil become a buffer for rainfall and low points.

Try placing a raised bed beneath a modified downspout to slow the water where it flows in concentration. To prevent a washout, fit a flex drainage pipe onto the spout to distribute water evenly in the bed or to direct water further out into a bed placed in the landscape.

Create layers of permeable material at the base of the bed to accelerate drainage. Compost and well-draining soil atop sand and two or three inches of gravel improve flow out of the bed to reduce pooling conditions.