How To Build a Rain Garden: The Complete Guide

How To Build a Rain Garden: The Complete Guide

Building a rain garden is a great way to reduce water pollution. Rain gardens collect extra rainwater from hard surfaces like driveways, sidewalks, roofs, nearby hills, and much more. By collecting extra rainwater in the soil in your rain garden, you’ll prevent excess water from accumulating under your home or in gutters or polluting local bodies of water. 

In this article, we’ll go over the simple steps you can take to build a rain garden over the course of a few days. We consider this a beginner-level project that most individuals can take on. 

You’ll also learn about:

  • Tools and skills you’ll need to build a rain garden
  • Estimated cost and time
  • How to know if you need a rain garden
  • Benefits of a rain garden

Tools and Skills You’ll Need

A rain garden protects and nurtures the land in your yard and the environment by using rainwater to support your plants rather than creating buildup in your gutters

Here are the tools, materials, and skills you’ll need to create one efficiently: 

Tools:

  • Wheelbarrow
  • Spade
  • Level

Materials: 

  • Native, deep-rooted plants, flowers, and grasses
  • 1 to 1.5-inch river rock
  • Landscape fabric (optional)
  • Decorative rocks and boulders
  • PVC pipe (optional)

Skills Required:

  • Planting
  • Digging 
  • Preparing plants
  • DIY Installation (Beginner-friendly)

Estimated Cost and Time

Most rain gardens will take several days to build, likely two to three days. Cost can vary significantly based on the plants you choose, the tools you already have, compost, rock, and how large you want your rain garden to be. As a general estimate, a rain garden can cost between $500 to $1,500. 

How To Build a Rain Garden

1. Gather Your Supplies

Start by taking inventory of your yard and current supplies. Do you already have a wheelbarrow, rocks, plants, a spade, PVC pipe, etc.?

Make a list of any materials you don’t have and work to acquire the supplies by purchasing them online or through a local garden store or borrowing them from friends or family.

2. Identify the Ideal Location for Your Rain Garden

Examine your yard and identify where would be the best place to set up your rain garden. As a general rule of thumb, rain gardens should be at least 10 feet away from your house to prevent flooding or water damage to your home. In addition, it’s best to build the rain garden in a place where water tends to gather after rain.

Never build your rain garden over underground utility lines or a septic system. We recommend calling 811 (national number) to have your utility areas marked before you begin digging to create your rain garden. 

A rain garden should also be located in an area that gets full sun for at least half of the day. A natural slope of at least 1% grade that leads from where water collects, such as your driveway or roof, down to your rain garden is ideal for providing your rain garden with plenty of water and soaking up extra rainfall. However, a relatively level area is still ideal for keeping digging to a minimum. 

3. Check the Scope of Your Yard

Check the scope of your yard using a level and long, straight board. Look for a minimum slope of 1 inch in 4.5 feet to allow water to flow into your rain garden naturally. If your land doesn’t have this kind of slope, you’ll need to create the necessary slope to improve your yard’s drainage. 

We recommend using beautiful river rocks and a combination of large decorative rocks to create a channel for water to funnel into your garden. You can also reinforce this channel with PVC to create a more substantial flow, especially if your garden is over 30 feet away from a downspout. 

While creating your rain garden, consider making an overflow zone to account for the biggest storms each year that will likely overflow your rain garden. To account for this, create an overflow zone in a slightly lower area on one side with rocks to channel water away after your rain garden is full. Ensure that this will not channel excess water toward your home or neighbors’ homes. 

4. Determine Your Garden’s Depth and Porosity

The size and depth of your rain garden should be determined by how quickly the soil absorbs water. Typical rainfall in your area should fill the majority of your rain garden but drain away within 24 hours. 

To calculate how deep and big you should make your rain garden, create a small test hole in your ideal rain garden area. Then, fill it with water and monitor it to see how quickly it drains. Once you know how long it takes for water to drain from your soil, consider how much water your garden will be flooded with during the average rainfall in your area. You’ll also want to think about the type of soil you have. If your sandy soil quickly drains, it can be dug deeper. However, soil that doesn’t drain quickly, like poor draining clay soil, should not be dug as deep because the water will remain in your garden for far too long. 

Next, consider the porosity of the soil. Place a coffee can in a dug hole in your garden area and fill it with water. Monitor the coffee can to see how long it takes the water level to drop. For example, if your water level drops by 1 inch in an hour, it’s safe to assume that it’ll drop 2 inches in two hours. If this is the case, your garden soil can absorb about 24 inches of water in a day, so the ideal depth of your garden is 24 inches. 

Consider the following chart adapted from the Oregon Rain Garden Handbook for rough estimates of how deep your rain garden should be: 

Drainage Rate Suggest Rain Garden Depth
½ to 1 inch per hour 12 to 24 inches
1 to 2 inches per hour 6 to 8 inches
More than 2 inches per hour 6 inches

5. Your Garden Size

For your rain garden design, consider the estimated volume of water that would flow into your rain garden based on the garden’s location and the spout that would feed it during the average storm in your area. In general, rain gardens should be the size of 10% of the water-resistant surface or impervious area draining into your garden, which includes areas like your roof, sidewalks, driveway, and concrete areas.

Even if you cannot create a huge rain garden to accommodate all the rainfall in your area, remember that a small rain garden can still provide significant benefits. Rain gardens that are smaller than ideal can still typically handle the majority of stormwater runoff.

Once you’ve determined the size and location for your rain garden, take time to strip away any lawn by cutting off the roots with a sharpened spade or with a sod cutter. Create a flat bottom so that the rain garden can absorb the water evenly. If your rain garden is on a slope, you can use excavated soil to bolster the low spot of the garden, allowing it to retain and absorb runoff water. Next, install your PVC piping into a dug trench to carry water from your gutter downspouts into your garden. 

6. Select Your Plants

We recommend choosing between three to seven new plants with a similar look because this will create a stunning garden and prevent your plants from being wiped out by the same pest. 

Plant growing zones and soils can affect what kind of plants you choose for a typical garden. However, rain garden plants tend to be standard because they need to be filled with plants that can tolerate “average to moist” water levels. In addition, it’s wise to select several plants that thrive in “average to dry” water conditions. This may seem counterintuitive at first, but consider how your rain garden will do during drier seasons. If all of your plants are moisture-loving, they will soon wither once the rain has drained out of your garden. 

Rain gardens should also be made of native plants, such as wildflowers, shrubs, and grasses. These plants typically have deep roots, with some of their roots burrowing down 10 feet or more, which is ideal for soil aeration. Native plants also tend to be easier on the environment because they’re indigenous and meant to be in your area’s zone and soil conditions, which will likely require less maintenance. Generally speaking, fertilizers should not be necessary, and native plants should only require minimal weeding once the first summer of growth has passed.

When placing your plants, put your moisture-loving plants in the center of your garden, which typically stays the wettest longest after a storm. Place “average to dry” plants on the edges of your garden to create a nice balance. Once planted, cover the rain garden’s soil with a 3-inch layer of mulch to keep the area moist and to help prevent weeds. 

7. Monitor Your Rain Garden Closely 

Your rain garden’s first year is essential to its success as rain gardens can be more delicate at first. We recommend taking the following steps to protect your rain garden and plants: 

  • Water your new garden weekly (about an inch) during drier spells. Native plants will become more tolerant of dry conditions after maturity, but it’s good to baby them and make sure they receive enough water until they’ve matured.
  • Use large decorative rocks strategically at your rain garden’s entrance to discourage heavy rain from washing away younger or weaker plants.
  • Use shredded hardwood mulch weekly. We recommend skipping pine bark or wood chips which may wash away. 
  • Dig a berm into the terrace of your garden on the lower side to allow half of the rainfall to flow out during the first year. The berm will enable younger plants to mature without overwhelming them with a tremendous amount of water. Later on, your rain garden should be able to handle typical rainstorms on its own.

How Do I Know I Need a Rain Garden?

Rain gardens have many personal benefits, as well as environmental benefits for your home, city, and wildlife. 

Here are several reasons why you may need a rain garden

  • If you live in an area with extensive rainfall.
  • To prevent your gutters and storm drains from overfilling.
  • To protect local bodies of water from additional water pollution.
  • To decrease your risk of mosquitoes and other pests by preventing standing water from building up in your yard.
  • To protect neighbors who live downhill from you from flooding and erosion problems.

Benefits of a Rain Garden

Rain gardens are landscaped areas planted with native plants, such as native grasses and flowers. Rain gardens act like sponges and absorb rainwater. During rain or a storm, the rain garden will fill up with several inches of water, then slowly filter the water into the soil and plants, rather than the rainwater running off into gutters, storm drains, or even flooding your home. It’s estimated that rain gardens absorb 30% more water into the ground than the typical lawn, making them valuable to any homeowner’s yard. 

This additional absorption is significant because studies have demonstrated that as much as 70% of pollution in streams, lakes, and rivers is carried there by stormwater streaming into the body of water. Not only does rainwater runoff carry pollutants into local bodies of water, but it can also cause thermal shock to animals in the water. When water temperatures are suddenly changed by fast-flowing runoff, animals in the water can undergo a sudden temperature change and may die or be forced to move out of the water due to the rising temperatures. So, by creating a rain garden, you’re helping to protect your home from water buildup, creating a beautiful garden for yourself, and protecting your local bodies of water from greater pollution. 

In addition, rain gardens create the following benefits for many homeowners and gardeners: 

  • Protect streams, ponds, coastal waters, and other bodies of water
  • Remove standing water in your yard, which can help with pest management
  • Reduce mosquito breeding and infiltration
  • Decrease your risk of home flooding
  • Filter pollutants from runoff
  • Conserve water
  • Increase the presence of beneficial insects, like pollinators, by providing them with flowers or food sources
  • Create a beautiful habitat for butterflies and birds
  • Add foliage to your yard without adding the need for mowing or heavy maintenance
  • Increase your property value
  • May allow you to qualify for rebate and incentive programs

Rain gardens also don’t need fertilizer, pesticides, or herbicides to thrive, so they’re less expensive to maintain and an eco-friendly choice compared to other types of plants and gardens. 

Final Thoughts

Rain gardens are a massive benefit to homeowners, wildlife, and the environment that shouldn’t be underestimated. Now that you know everything there is to know about how to build a rain garden, we hope you’ll have fun taking on this eco-friendly, sustainable, and beautiful gardening project. These easy-to-maintain gardens will provide beauty to your yard for years to come. 

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