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A rain garden is a landscaped area that collects and filters stormwater runoff from roofs, driveways, sidewalks, and other hard surfaces. Rain gardens help reduce flooding, erosion, and pollution by allowing water to soak into the ground instead of flowing into storm drains or nearby waterways. Rain gardens also provide habitat for birds, butterflies, and beneficial insects, and enhance the beauty of your yard.
Rain gardens are not ponds or wetlands. They are designed to drain within 24 hours after a rain event, preventing mosquito breeding and waterlogging. Rain gardens can be adapted to any soil type, sun exposure, and size of your property. The key is to choose native plants that are suited to the conditions of your rain garden.
Benefits of Rain Gardens
Rain gardens offer many benefits for you, your community, and the environment. Some of these benefits include:
- Reducing stormwater runoff. Stormwater runoff is the excess water that flows over hard surfaces when it rains or snows. It can carry pollutants such as fertilizers, pesticides, oil, and bacteria into streams, lakes, and rivers, harming aquatic life and water quality. Rain gardens capture and filter stormwater runoff, reducing the amount of pollutants that reach our waterways.
- Recharging groundwater. Groundwater is the water that fills the spaces between soil particles and rocks underground. It provides drinking water for many people and supports stream flows during dry periods. Rain gardens allow water to infiltrate into the ground, replenishing groundwater supplies and maintaining natural hydrologic cycles.
- Creating wildlife habitat. Rain gardens attract a variety of wildlife, such as birds, butterflies, bees, and other pollinators. They provide food, shelter, and nesting sites for these animals, enhancing biodiversity and ecological health. Rain gardens also support native plants that are adapted to local climate and soil conditions, preserving our natural heritage.
- Beautifying your landscape. Rain gardens add color, texture, and interest to your yard. They can be designed to complement any style or theme of your landscape, from formal to naturalistic. You can also use rain gardens to create focal points, define spaces, or screen views.
How to Build a Rain Garden
Building a rain garden is not difficult, but it does require some planning and preparation. Here are the basic steps to follow:
- Choose a location. The ideal location for a rain garden is where water naturally flows or collects on your property, such as near a downspout, along a driveway, or at the bottom of a slope. Avoid areas that are too close to buildings (at least 10 feet away), septic systems (at least 35 feet away), or utility lines (call 811 before you dig). Also avoid areas that are too shady (less than six hours of sun per day) or too wet (where water stands for more than two days after a rain).
- Determine the size and shape. The size of your rain garden depends on how much water you want to capture and how much space you have available. A general rule of thumb is to make your rain garden about 10% of the area that drains into it. For example, if you have a 1,000 square foot roof that drains into your rain garden, your rain garden should be about 100 square feet in size. You can use any shape that fits your site and preferences, such as oval, kidney-shaped, or rectangular.
- Dig the basin. The basin is the depression that holds the water in your rain garden. The depth of the basin depends on your soil type and infiltration rate. Sandy soils drain faster than clay soils, so they need deeper basins than clay soils. You can test your soil infiltration rate by digging a hole about 12 inches deep and filling it with water. If the water drains within four hours, you have sandy soil; if it takes longer than 24 hours, you have clay soil; if it takes between four and 24 hours, you have loam soil. The recommended depths for different soil types are:
- Sandy soil: 18 to 24 inches
- Loam soil: 12 to 18 inches
- Clay soil: 6 to 12 inches
- Amend the soil. The soil in your rain garden should be loose and rich in organic matter to allow water infiltration and plant growth. You can improve your existing soil by adding compost or other organic amendments such as leaf mold or aged manure. Mix the amendments with the native soil at a ratio of about one part amendment to three parts soil. You may also need to add some sand or gravel to improve drainage, especially if you have clay soil. Avoid using topsoil or peat moss, as they may contain weed seeds or pathogens, or alter the pH of your soil.
- Create a berm. A berm is a raised edge around the rain garden that helps contain the water and prevent overflow. You can use the soil that you dug out from the basin to create the berm, or use other materials such as rocks, bricks, or wood. The height of the berm depends on the depth of your basin and the slope of your site. The steeper the slope, the higher the berm needs to be. The berm should be at least six inches high and slope gently away from the rain garden. Make sure to compact the berm well and cover it with mulch or plants to prevent erosion.
- Connect the source. The source is where the water comes from, such as a downspout, a sump pump, or a swale. You need to connect the source to your rain garden with a pipe, a trench, or a channel that directs the water into the basin. You can use flexible or rigid pipes, such as PVC or corrugated plastic, or dig a shallow trench lined with gravel or stones. You can also create a natural-looking channel with rocks, plants, or logs. Make sure the pipe, trench, or channel has a gentle slope (about 2%) and is wide enough to handle the flow of water. You may also need to install an overflow outlet at the opposite end of your rain garden in case of heavy rain events that exceed the capacity of your rain garden.
- Select and plant native plants. The plants are the most visible and attractive part of your rain garden. They also play an important role in filtering pollutants, absorbing water, preventing erosion, and providing wildlife habitat. The best plants for your rain garden are native plants that are adapted to your region and can tolerate both wet and dry conditions. Native plants also require less maintenance and watering than non-native plants.
- Maintain your rain garden. Your rain garden will require some maintenance to keep it functioning well and looking good. Here are some tips for maintaining your rain garden:
- Watering. Your rain garden plants will need regular watering during the first year or two until they are established. After that, they should be able to survive on rainfall alone, except during prolonged droughts. Water your rain garden deeply and infrequently, rather than shallowly and frequently, to encourage deep root growth and drought tolerance.
- Weeding. Your rain garden will need some weeding to prevent invasive or unwanted plants from taking over. Mulching can help reduce weed growth, but you may still need to pull out weeds by hand or use a hoe or cultivator. Avoid using herbicides, as they may harm your rain garden plants or contaminate the water.
- Pruning. Your rain garden plants may need some pruning to keep them healthy and tidy. Prune dead, diseased, or damaged branches or stems as needed. Cut back perennials and grasses in late fall or early spring to remove old growth and stimulate new growth. Trim shrubs and trees to maintain their shape and size, and remove any suckers or unwanted shoots.
- Mulching. Your rain garden will benefit from a layer of organic mulch around the plants. Mulch helps conserve moisture, suppress weeds, prevent erosion, and enrich the soil. Use shredded leaves, pine needles, wood chips, or other natural materials as mulch, and replenish it as needed. Avoid using plastic, rubber, or stone mulch, as they may interfere with water infiltration or create heat stress for the plants.
By following these tips, you can keep your rain garden in good shape and enjoy its beauty and benefits for years to come.
