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Rain Gardens – Digging Deeper

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Rain gardens are popping up everywhere. You will find them on college campuses and office parks, in mall parking lots, along city streets and multiuse trails. They have grown in popularity over the last several years, in response to the many problems stormwater causes in the landscape.

When it rains – especially a heavy rain – we see flooding, erosion, and pollution from stormwater runoff. Just the first inch of rain during a storm collectively does the most harm.

The good news is local use of rain gardens (even on your own property!) can help to reduce flooding, erosion, and pollution over a broad region.

The Benefits of a Rain Garden

A rain garden on your property provides numerous benefits, including:

  • Intercepting water and provide habitat for birds and wildlife
  • Reducing stormwater runoff by 30% compared to a traditional turf lawn
  • Adding natural beauty

It is not just another garden bed and does not need to be limited to perennial wildflowers and grasses. Shrubs and trees can also be used in rain gardens to achieve increased absorption, retention, and beauty.

Planning Your Rain Garden

When planning a rain garden, you need to determine what is known as the infiltration rate of your soil, or how quickly water drains through it. This will indicate whether your soils can support a rain garden. You can test it yourself in 4 easy steps:

  1. Dig a hole 1’  deep, being careful not to disturb the sides or compact the soil in the hole.
  2. Pour 444 mL (1”) of water into the hole and let it drain completely
  3. Fill the hole with water again and place a ruler in the center flush with the bottom to measure the depth
  4. Wait 15 minutes, measure the water depth again then multiply the result by four to determine the infiltration rate. Rates of .5 to 8 inches in an hour are sufficient for rain gardens.

Next, consider the location and size of the rain garden.  The Philadelphia Water Department recommends sizing your rain garden to be 20-30% of your impervious surfaces (roof, driveways, patios, and walkways).  The rain garden should be a minimum of ten feet away from the foundation of your house and your property line and in the lowest spot of the yard. The area should have a 1% slope away from your house for proper drainage. The rain garden will need either an outflow or a drain for larger storm events to prevent flooding. Make sure that the direction of the discharge is away from your house and your neighbor’s property.

When digging the rain garden, if your soil is rich with organic matter, two to three inches of depth will be sufficient. If it’s not and you need to amend it, dig down five to six inches and add compost. Always use PA 1-Call  before you dig, to make sure you are clear of unseen obstacles underground.  Taper the edges of the rain garden toward the center to prevent erosion. 

Purple coneflower is a great choice for a raingarden.

Selecting Plants

And now for the exciting part: deciding what to plant. The funny thing about a rain garden is that most of the time, it is dry! While you might think wetland plants would be best, floodplain plants that can handle periods of inundation and drought are actually ideal. Basically, a rain garden functions like a small floodplain where water can stop, slow down, infiltrate into the soil and be absorbed by plant roots. The next question to ask is what plants are common to floodplains?

Depending on the size of your rain garden, planting a tree in it might not make sense. But if it does, a tree can be a fantastic focal point. In our region, you have a variety of native choices:

  • canopy trees: red and silver maples, sycamore, river birch, pin oak, swamp white oak, and black gum. 
  • understory: black willow and sweet-bay magnolia

Bald cypress is a great southern species, too. As our area continues to warm up, using more southerly species may be a way to increase the long term vitality of your landscape.

The shrub layer of floodplains offer a rich palette of plants from which to choose. Highbush blueberry, red chokeberry, and black chokeberry look lovely and provide edible fruit. Buttonbush, arrowwood, winterberry holly, ninebark, meadowsweet, sweet pepperbush, possumhaw, red twig and silky dogwoods offer a variety of color, texture and seasonal interest to round out a rain garden. Once established, shrubs require minimal maintenance.

Thinking of your rain garden as a habitat with niches to fill can help guide design and plant selection. Plan on a variety of heights and moisture tolerances between the center and edges. Plant low growing cool season bunch grasses for early season cover, wildflowers for summer color, and shrubs for height and fruit.

Whether you plant trees, shrubs, wildflowers, or grasses, rain gardens can provide beauty, functionality, and habitat for your landscape. Dig deeper and decide for yourself what type of rain garden fits your landscape and start helping your community by reducing stormwater runoff at home. Many small actions can really make a difference.

Willistown Conservation Trust’s Rushton Conservation Center features a rain garden designed by Jonathan Alderson Landscape Architects. It is includes sweetbay magnolia and sweet pepperbush. A variety of wildflowers and grasses were planted as plugs and seed. Swamp milkweed, butterfly weed, purple coneflower, bee balm, beardtongue, mountain mint, and asters fill the basin with seasonal color and attract pollinators all summer long. The circular driveway around the rain garden is pitched inwards to drain runoff during storms. A surface drain in the rain garden directs overflow to a nearby underground stormwater basin.

This article was originally published in County Lines Magazine – May 2020 Issue.

Create Your Own Meadow – Step 3: Preserve

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Early May – Early October: Once your wildflowers are planted, regularly inspect your meadow to ensure that invasive weeds are not colonizing the space. Hand pulling or cutting weeds below the height of native species should help to manage any invasives that may creep into your meadow.

Year Two and Beyond: Mow the entire meadow once a year in late March to early April to a height of about 6 inches — before the young wildflowers start pushing through the grass. Although some landscape professionals recommend mowing meadows in the fall as well, leaving plants unmowed over the winter provides important food and shelter for wildlife during the harsh winter months. Should you decide to mow a second time in the fall, wait until the year following installation to give the young wildflowers a chance to establish.

Wildflower plugs generally take three years to fully mature, so patience is required, but the result is well worth the wait!

Create Your Own Meadow – Step 2: Plant

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Mid April – Early May: Once your wildflower plugs arrive, it may be tempting to lay out plants in neatly arranged rows, but clustering plants together while still paying attention to plant spacing will echo the more organic patterns found in nature.

Planting wildflower plugs
It’s a great group or family project

In addition, wildflowers planted in clusters with several plants of the same species within a few feet of each other will also help to attract more pollinators. Use a handheld auger (2” +/- in diameter) or shovel to open holes for your wildflower plugs. Then you can easily insert each plug in the hole and tamp the soil around it.

Progress just 3 months after planting. This is in front of the Trust office.

Creating Your Own Meadow – Step 1: Prepare

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Depending on the size you want, it’s not too late to plan a meadow for your property. Native wildflowers and native grasses have deeper root systems than their non-native counterparts. These roots help strengthen soil against erosion, absorb more rainwater, reduce stormwater runoff and even sequester and store carbon.

Select your location; this was the front lawn of the Trust’s office on Providence road.

Select a location for your meadow that is generally sunny and well-drained. Existing lawn areas or fields are ideal. The size of the meadow should be determined by how much space you are willing to dedicate to the project and your budget. As a guide, a quarter-acre meadow would require approximately 2,700 wildflower plugs planted 2 feet on center.

February – Late March: Work with a landscape professional or reputable nursery that specializes in native plants to place an order for wildflowers that can be scheduled to arrive for installation in mid-April – early May.

Late March – Early April: Begin preparing the meadow area by mowing it to a height of 2-3 inches. Continue to mow the project area until you are ready to install the wildflower plugs.

Beautiful and colorful variety at the Trust office meadow

For inspiration, feel free to stop by the Willistown Conservation Trust office and have a look at our meadow. It’s been established for nearly 10 years and shows what you can look forward to.

Variety is the Essence of Life

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The old saying goes that variety is the spice of life. In nature, variety is the very essence of life.

Hopefully you’ve read and enjoyed our recent blog posts about the importance of riparian buffers and tips for planting trees and shrubs, if you haven’t yet please take a look. You’ll find helpful guidance, which will be handy for World Planting Day coming up on October 22!

An important aspect of healthy riparian buffer is planting a variety of species, which will help support a variety of insects, animals, bacteria, fungi and other living things. A variety also looks nice, providing different colors and textures in your landscape.

To help you, we’ve assembled a collection of our favorite native trees and shrubs that grow well in riparian buffers.

You can also download a PDF here for future reference.

For detailed information about each of these, you can consult wildflower.org. You can also talk with a reputable native plant nursery or landscape designer about what variety of plants to select for your particular area.