By Andrew Bunting, PHS VP of Horticulture 

As weather patterns continue to change and there are more instances of flooding and inundation from significant rainfall, it will become more and more necessary to plan for and develop home landscape infrastructure to help capture and mitigate stormwater runoff and rainfall. The good news is that the home gardener can use many methods to efficiently utilize rainfall throughout the year. 

1. Save the Water 

There are many ways that stormwater can be captured from the gutter systems of houses. There are various sizes of water tanks and rain barrels that can be easily adapted to capture rainwater from homes. This water then can be used on an as-needed basis to water and irrigate plants in the garden.

PHS manages the Philadelphia Water Department's (PWD) Rain Check program, which provides an innovative way to water your garden and improve your property while decreasing stormwater runoff. The program offers:

• Rain barrels
• Downspout planter
• Rain gardens
• Permeable pavers

Ideally, every downspout on the house could be retrofitted with a rain barrel, with the additional options listed above as space permits.

Interested in getting a rain barrel, rain garden, or downspout planter for your own yard or garden? Start by participating in a one-hour Philadelphia Water Department (PWD) Rain Check educational workshop. 

2. Plant Trees 

One of the easiest solutions to mitigate extra rainfall is to plant large shade trees or street trees that have aggressive root systems that will absorb large amounts of water. Some of these trees include the London plane tree. Platanus x acerifolia Exclamation!™ is an introduction from the Morton Arboretum and the Chicagoland Grows Program which has a very upright pyramidal habit. It is an exceptional selection which has been recognized by the Pennsylvania Horticultural Society’s Gold Medal Plant Program. It makes both an excellent street tree and shade tree and can survive both very dry and very wet conditions.

In addition, there are many selections of the red maple, Acer rubrum that are excellent for absorbing water during periods of inundation. Some of these selections include October Glory®, Red Sentinel™, and Red Sunset®. As the name implies, red maples are famous for their exceptional red fall color. This native maple is one of the very best street trees for its adaptability to a host of urban conditions including drought, as well as the ability to grow in very poorly drained areas.

Nyssa sylvatica, the black tupelo is another fantastic native tree that should be planted to mitigate the impacts of stormwater. There are many outstanding selections including Firestarter® with an upright pyramidal habit, and Green Gable™, which has a more rounded canopy. Red Rage® and ‘Wildfire’ have exceptional fire engine-red fall color.  

3. Installing a Rain Garden 

There are many types of rain gardens that can be considered for the home garden. Typically, soil is excavated out of the garden, creating a depressed area that is below the existing grade on a property. Additionally, the surrounding soil can be graded, so when it rains the stormwater runoff is directed toward this depressed or sunken portion of the landscape. If this area is fairly large and has a reasonable depth, it can capture large amounts of precipitation during a rain event. This area will fill up with water and over time the accumulated water will slowly percolate into the surrounding soil, therefore significantly reducing stormwater runoff. For a rain garden to be successful, it should be planted with shrubs and perennials that can withstand being submerged for extended periods of time and can help absorb excess moisture.  

Some great choices of perennials for the rain garden include several sedges including Carex amphibola, C. comosa, C. emoryi, C. stricta and C. volpinoidea. Many ferns can take these periods where they are very wet, including: the lady fern, Dryopteris marginalis Athyrium filix-femina; marginal wood fern, ostrich fern, Matteuccia struthiopteris; sensitive fern, Onoclea sensibilis; cinnamon fern, Osmunda cinnamomea; and the royal fern, Osmunda regalis var. spectabilis.

One of the most beautiful of all the rain garden perennials are the Joe-pye weeds. These robust and stout plants are characterized by an abundance of dome-shaped purple flowers in the late season. Eupatorium purpureum ‘Gateway’ can reach 5-7’ feet tall and the new ‘Little Joe’ is a much more diminutive form. The cardinal flower, Lobelia cardinalis has bright, vibrant red flowers that is a magnate for the Ruby-throat Hummingbird. Other great flowering plants included the pink flowered turtle flower, Chelone lyonii ‘Hot Lips;’ Hibiscus coccineus, which reaches nearly eight feet tall with stunning late summer red flowers, and the white, candelabra-like flowers of the culver’s root, Veronicastrum virginicum, which makes a great architectural statement. 

The habitat in the rain garden can be further developed by adding shrubs. There are several shrub-like hollies that make a great statement in the rain garden. In the wild, the winterberry, Ilex verticillate, grows on the edge of ponds and lakes making it a perfect plant for wet areas in the garden. This multi-stemmed shrub is covered in very ornamental berries from September to March. ‘Winter Red’ has an abundance of bright red fruits. ‘Winter Gold’ has an equal abundance of salmon-orange fruits. ‘Maryland Beauty’ is a heavy-fruiting selection. For good fruit, it's suggested that you also include a male pollinator such as ‘Southern Gentleman’ in the garden.

The inkberry holly, Ilex glabra is a small to medium-sized evergreen shrub that thrives in wet soils. The narrow, shiny, evergreen leaves are great in combination with other plants with ornamental winter stems and winter berries. ‘Shamrock’ is a more diminutive selection and Ilex glabra Strongox® is a new selection that is being promoted as a boxwood substitute. The native buttonbush, Cephalanthus occidentalis is another great shrub to consider. At maturity, it can reach up to ten feet tall. In mid-summer it is covered with an abundance of orb-like white flowers. Many of the native butterflies, including the swallowtails, are attracted to the flowers of the buttonbush.

Many of the red-stemmed dogwoods are also excellent for winter interest and can thrive in rain garden conditions. One of the best is Cornus sericea ‘Cardinal.’  ‘Cardinal’ has stems that reach up to seven feet tall. In the winter, the stems turn a brilliant pinkish-orange. The stems are often offset best with an evergreen backdrop, such as the inkberry holly or the white cedar, Chamaecyparis thyoides. 

In addition to being a great landscape feature that captures water and mitigates stormwater, the rain garden adds considerable beauty to the garden and landscape. Additionally, the rain garden plays an important role in filtering out pollutants from runoff from the garden.