Rain, rain, come my way. Feed the precious land today.
Water is a precious commodity, more precious than gold. It’s becoming ever more crucial for us to protect and preserve groundwater. Our modern civilization has stripped away much of the vegetation and topsoil and covered the earth in hard surfaces, such as asphalt and cement.
Hard surfaces prevent rainwater from soaking into underground aquifers and feeding into streams and lakes. Rainwater that does make it into streams and lakes is usually polluted with chemicals and waste that harm the ecosystems.
Rain gardens can be part of the solution.
What is a rain garden and why is it important? A rain garden is a beautiful way to nurture the environment, dress up your yard, protect your home, and manage the runoff of rainwater.
It’s a tool to improve drainage by capturing storm runoff from the roof, driveway, or other hard surfaces. The system funnels the rainwater into a natural reservoir or depressed area in the landscape – a temporary holding basin – and allows that water to soak into the soil. The plants in the rain garden benefit from the water, but also hold the groundwater in reserve.
Rain gardens benefit the environment in many ways. They aid in flood control after a rainstorm and help to protect and preserve groundwater by creating a natural trap to hold the water in the plant roots. The garden plants’ deep roots tap into the ground to soften soil and create channels through which water can flow, redistributing moisture and encouraging the growth of beneficial microorganisms that break down organic compounds and remove nitrogen. The plants absorb the water and nutrients from the runoff and release water vapor back into the air.
Rainwater contains 70% of the pollution that ends up in our streams, rivers, lakes, and ponds. Rain gardens can help to improve water quality in these bodies of water, because it prevents polluted runoff. The plants in the rain garden filter out the pollution and hold the water in the ground, replenishing or recharging the groundwater supply.
The whole ecosystem benefits from a rain garden. Rain gardens encourage wildlife biodiversity, because they attract and provide shelter for birds, butterflies, and other wildlife.
These gardens have a more personal benefit for the homeowner. They encourage the rainwater to seep quickly into the soil, away from your house. You can direct the rainwater from downspouts away from the foundation of your house through various means, such as PVC piping, a stone channel, or by grading your yard so the rain garden sits lower than your house. The plants keep the soil around them soft and aerated promoting better absorption of the water into the network of deep plant roots.
In some communities, a rain garden may also provide a tax break, since it reduces storm drain usage and keeps pollutants, such as lawn chemicals (which we shouldn’t be using!) from flowing into the storm drains. Additionally, it’s bound to boost your property value, because it protects your foundation.
The recommended grade from house to rain garden is 2%. The rain garden should be at least 10 feet from your house, to protect the foundation. Be careful not to locate your garden over a septic tank or underground utility lines.
Build a berm around a low spot in your yard. To funnel the water, lay underground 4” PVC pipe or construct a rock channel lined with river rock to direct the flow of water to your garden. If you get one or two really big storms a year, create an overflow area that’s lower than the rest of the garden. This will channel away any excess water when the garden is filled with runoff.
You want soil that holds the water but also allows for slow drainage. If your soil has too much clay in it, replace it with half sand, one-quarter compost, and one-quarter topsoil.
The size of your rain garden will be determined by how quickly water is absorbed. Estimate the amount of water that would come off your roof by the square footage of your roof and the number of inches of rainfall in an average storm. That will help you determine the size of your garden. A good rule of thumb is 20-30% of the size of your roof or driveway, whichever one provides the runoff.
You can test water drainage by digging a small hole about the size of a coffee can. Fill it with water and watch to see how quickly the water absorbs into the ground. If the water drops by a half inch within an hour, it can be determined that it will drain an inch in two hours. So, the garden will be able to absorb a foot of water in 24 hours. Water should drain away within 24 hours. The ideal depth of your garden should then be one foot.
If you don’t get the sizing just right, don’t worry. Even a small rain garden will reap big benefits.
What should you plant?
Native plants are best. They tap deeply into the soil, providing aeration and pathways for water flow, and they’ll thrive without adding stress to your environment. You will still need to water your garden during dry periods, but native species better adapt to these conditions. Native plants also attract pollinators and birds.
Trees and large shrubs deflect rain and slow down the runoff, which allows for better absorption into the soil. Tall grasses suck up water and filter it to trap pollutants and prevent soil erosion into storm drains and bodies of water. Shorter, more mature plants with deep roots are better able to hold the soil and water.
Use a mix of plants that are suitable for your zone. Plant one-third to one-half of your garden with native grasses, sedges, and rushes. They have very deep root systems. Add wildflowers, flowering perennials, shrubs, asters, daylilies, canna, iris, sedum, coneflower, artemisia, ferns, and small trees.
It’s best to plant your rain garden with seedlings or “plugs,” since seeds are easily washed away in the rain and take much longer to establish themselves in the landscape.
Experts advise locating perennials, woody, and native plants in the center of your garden, where there will be more water during a storm. They’re more tolerant of soggy soil. Then add plants around them that can handle periodic standing water. Set hardy plants that prefer drier soil around the marginal areas of your garden.
After planting, water well and mulch with compost or shredded hardwood. Bark chips are too light and may wash away in the rain. You may also want to add some larger sized rocks to slow down the flow for better absorption.
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