How to Build a Rain Garden in Your Backyard [Step-by-Step]

Do you happen to be living in one of the rainiest states in the United States of America? Are you a frustrated spectator of the rainwater pooling in your yard and entering your basement every rainy season, dampening your precious vintage comic collection in the process?

If the answer my friend is a yes, then you need to build a rain garden full of deep-rooted, colorful plants in your yard to soak up the excess rainwater while spreading happiness around yourself and every other person who comes across it. This article’s job will be to show you exactly how with a detailed step-by-step guide.

What is a Rain Garden?

A rain garden is basically a land area with a particular class of water-absorbent plants (usually colorful perennial flowers and native plants) to absorb stormwater into the ground.

To elaborate, a rain garden is that bowl-shaped place in the ground to which you can channel the water run-off carrying pesticides, pollutants and all kinds of dirt from going into the storm-drain straight with the help of a swale or plastic piping thus keeping the local water bodies pollution-free.

A rain garden prevents flooding and saves your lawn from turning into a pool whenever it rains.

Rain gardens drain within 12-48 hours, so you do not have to worry about it being a mosquito breeding ground.

Tools you will need

● Shovel or soil excavator

● Sod cutter

● Lawn-leveler rake

● Pvc pipes

● Wheelbarrow

● Trowel

● Watering can

Estimated time: 2-3 days

An Easy Step by Step Guide to Building a Rain Garden

Step 1: Plan & Design

To make your rain garden effective, you need to come up with a suitable plan and a design. You need to keep in mind the main goal of the garden which is water runoff collection from the adjacent area away from the storm sewers whether it is your lawn or driveway or carport or rooftop and design accordingly.

Also, you do not necessarily have to build only one rain garden in your yard. Some homes have multiple problem spots or impervious areas and to tackle that problem you can build more than one rain garden.

Step 2: Select an appropriate location

The goal is to intercept runoff from running down to the nearest storm drain and to channel away excess water from the impervious areas to the rain garden. So you should take a walk around your property and mark the stormwater runoff pathways i.e., see where the water goes and which way it travels and select the location for the rain garden to easily intercede that.

Also, select your location considering what you want to plant and their needs for sunlight because your plants need to grow and hold on strong to turn into a garden over time. A full sun location will make your job easier as most plants thrive in full sunlight.

You need to make your rain garden down a slope from the way of the downspouts or impervious areas in your yard. Also, the rain garden should be installed in a place at least 10 feet away from your house to ensure that the water does not get into the foundation of the house and also 25 feet away from a septic system. Do not select a place where water always pools.

Step 3: Soil test

The ideal soil for a rain garden is sandy loam. While you can see particles of sand in your soil if it is sandy, you could determine if your soil is truly sandy loam through a little test. Grab a handful of soil and dribble some water on it and turn it into putty and squeeze it in your hand. If it feels gritty and falls apart when you open your hand it is the ideal type of soil for your garden. On the other hand, clay soil will feel sticky and hold its shape if you do the same to it. Even if your soil is not fit for a rain garden, you can amend it later, but before you do that, you need to get a good idea about your soil.

Step 4: Select your plants 

Some prefer the aesthetic value of a rain garden over the practical one. Whatever your preference is, don’t forget to carefully consider the colors you want, bloom time, the height of the plants, needs for fertilizer, quality of seeds etc. to successfully build a garden.

Rain garden plants need to be highly resilient plants for both dry and wet seasons. Native plants are the most recommended plants as they grow well in local soil conditions. Pick any combination of flowers, shrubs and grasses which are native wild plants and which can grow in both full and partial sunlight. It is highly recommended to only pick nursery plants and to not pick plants collected from the wild.

Choose a variety of seasonal plants for your garden. Select separate plants for the basin and the berm or the top of the rain garden. The basin plants should be able to withstand being submerged in a pool of water for a short time and the berm plants must suit dry conditions and be shorter than the basin plants.

Related Read: How to Make a More Bird Friendly Backyard (12 Proven Ideas)

Step 5: Determine the size of the rain garden

The ideal size of a rain garden should be 7-20% of the total size of the impervious surface according to the U.S. Department of Agriculture which means you should measure the length and width of the total impervious surface area which may consist of your roof or driveway or anything else.

Step 6: Deciding the depth of the rain garden

The ideal depth of a rain garden or the pool is 4-8 inches, which means from the berm to the basin, there should be a distance of 4-8 inches. The depth determines how much water your garden will retain during a storm.

Step 7: Shape

Pick any shape that goes with the rest of your garden. You can color coordinate to make the garden look beautiful. Use a rope to outline the shape you have selected.

Step 8: A small percolation test

Dig a hole 8″ deep and the same in diameter on the site where you want to build a rain garden. Fill it with water and check the water level after one hour with a ruler. Deduct the inch/inches from the top of the hole to the water level from 8. If you multiply it by 24, you get the amount of water absorption in 24 hours and get an idea of how deep your rain garden surface should be.

Step 9: Digging up the site of the rain garden

To make digging up the soil on the site of your rain garden easier, strip it completely of grass with a sod cutter which you can rent on a 24 hours basis. Then use a soil excavator or a shovel and dig up the depression and flatten the bottom by stomping or using a leveling tool such as a lawn-leveling rake.

Also, you don’t always have to make a standalone rain garden as you see in the pictures. You can just dig a depression around your already existing perennial flower bed or shrubs for your tiny rain garden when you do not have much space left to build it separately.

Step 10: Digging up narrow trenches

Now dig up narrow trenches from the spots of the downspouts or the impervious areas towards the rain garden so that when it rains, the water runoff is carried to the rain garden. Follow a layout plan for digging the trenches to ensure the smooth passage of water runoff from the problem spots. You can also install an extended perforated Pvc pipe from your gutter in the trenches to carry water runoff to the rain garden. You can place colorful, round and small gravels over the pipe to hide it or to prevent erosion of the soil in the trench.

Step 11: Amending your soil

At least 23 inches or 60 centimeters of the rain garden depression should be filled up with a special soil mix to amend your existing soil if you do not have the soil fit for a rain garden. Stomp the soil as you fill up the garden site. The ideal soil mix for these 60 centimeters is 50-60% sand, 20-30% low clay top-soil and 20-30% compost.

Step 12: Making a berm

A berm is a wall for the rain garden to retain water inside it. The berm should have very gentle slopes. Use your remaining excavated soil to make ridges around the rain garden basin and stomp on it to make it smooth.

To prevent erosion you should plant grass on the berm area or find any other plant not higher than the plants in the basin.

Step 13: Plant your plants

Dig plant holes deep and wide enough to fit the plant plugs, but the depth should match the depth of the container your plant was in. After planting, fill up the hole and tamp around the root and water it. You will need to water the plants according to their type for at least the first four weeks unless rain does the job. Keep space between your plants to avoid making your garden overcrowded.

Spread two inches thick shredded mulch when you are done planting. Mulch is important as a preventive method against erosion and evaporation as well as weeds. You can check on the mulching on a yearly basis afterward.

Step 14: Maintenance

To make your garden grow and thrive, you need proper aftercare. Make sure to keep an eye on and take out all the weeds from the root regularly. Trim plants with thick stems with hand clippers or hand pruners. Also, you do not have to fertilize your rain garden as the soil mix itself is good enough.

For the first year or two, watering will be necessary for most rain garden plants during the summers but don’t overdo it. Look out for debris build-up in your rain garden. Re-mulch as necessary. Check the water inlets regularly for built-up debris and unclog them to let water flow smoothly into the rain garden.