How to Create a Rain Garden
Find a suitable location for your garden., Figure out how big your rain garden should be., Plot out the garden plan., Stake out the garden area., Determine how deep your garden should be., Dig out the garden area to the desired depth., If the garden...
Step-by-Step Guide
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Step 1: Find a suitable location for your garden.
It's easiest to install a rain garden in an area of your yard that water already flows to or through.
Your end goal is to reduce runoff.
You can usually identify a suitable area by examining your yard during a rain storm to see how water flows off it.
Rain gardens should be located at least 10 feet (3.0Â m) away from foundations to prevent basement flooding and structural problems.
They should never be located directly over a septic system, over underground utility lines--always call before you dig--or in a right-of-way.
In addition, rain gardens are not suitable for areas where the seasonal high water table level is less than 24" from the surface, as the water table will prevent infiltration of runoff water into the soil.
Finally, large rain gardens, or any rain garden that requires extensive excavation, should generally not be placed under large trees, as excavation may damage tree roots and excessive water can be harmful to some species of trees.
The more level the spot, the easier it will be to install your rain garden.
The rain garden site doesn't have to be perfectly level, but steeper slopes will require more excavation to make your garden deep enough to hold water, and slopes over 12% generally require too much excavation to be worthwhile.
A spot at the base of a steep slope is best.
Seemingly, the most obvious spot for a rain garden is a depression that already exists in your yard.
However, pooling or ponding may indicate that the water table is too high or, more commonly, that the soil has a low infiltration rate, which will make the area unsuitable for a rain garden.
To test for adequate drainage, dig a hole 6-8" deep and fill it with water.
The water should drain completely within 12 hours; if it doesn't, the spot is not suitable for a rain garden unless you do some extra work to prepare the soil (see Tips section below).
You are best suited to find a location that is suitable and redirect existing downspouts to it. -
Step 2: Figure out how big your rain garden should be.
The ideal size of your rain garden depends on the size of the area that drains into it and the soil in the rain garden.
Determine the area (in square feet or square meters) of the surface that will drain into your rain garden.
Watch the drainage pattern during a storm or carefully examine the contours of your yard to determine where the water will come from.
Then measure this, including, if applicable, the area of your roof and any paved surfaces that will drain into the garden.
The area of your rain garden should be proportional to the area it drains.
For sandy soils, the rain garden size should equal about 10-20% of the total drainage area, while for very clayey soils, aim to make your rain garden equal to 50-60% of the total drainage area.
Loamy soils require a rain garden area somewhere in between these two extremes, depending on their clay content.
These proportions can be reduced for deeper rain gardens (those which are more than 5" deep over most of their area) or those that are more than 30 feet (9.1Â m) from the primary sources of drainage.
All these numbers, however, are only guidelines.
A rain garden can't be "too big," and even if it's smaller than the guidelines recommend, it will still help reduce runoff. , It's a good idea to plan your rain garden on a sheet of graph paper or a computer design program before you start digging.
Keep in mind that rain gardens typically work best if they are curved and slightly irregularly shaped.
The longest side should be perpendicular to the slope. , With plan in hand, use stakes and string (or hose) to mark the perimeter of the rain garden. , The ideal depth for a rain garden depends on the slope of the garden area.
A flat area or one with a very gentle slope can be as little as 3-5" deep, while 6-7" works best for a 5-7% slope, and 8-10" works best for an 8-12% slope.
Add another inch or two if you plan to incorporate compost into the rain garden soil.
Excavating deeper is recommended, typically 16-24" down., It's important to get the bottom of the rain garden as level as possible so that runoff water will spread evenly in the garden rather than pooling in one area.
To ensure that it's level, use the following methods, working in one 5-foot wide section at a time. , Dig the entire area to the same depth, frequently measuring the depth from the string to the base of what will be the rain garden.
If the rain garden is situated on a slope, you will need to dig the uphill end out deeper than the downhill end to ensure the base is level.
Drive a stake at the uphill end and another at the downhill end.
Tie a string around the base of the uphill stake, and then run the other end of the string to the downhill stake.
Tie the string to the downhill stake so that the string is level over its entire length.
You can attach a line level to the string to check that it's level, or you can use a standard carpenter's level.
Start at the uphill end and dig down from the string to the desired depth.
The amount of soil you actually need to remove will be less and less as you move farther downhill, and you may even need to fill in the bottom (downhill portion) of the garden with some of the soil you removed from the top (uphill portion).
As an example, suppose you had a 10' long section of your rain garden with a 10% slope (meaning that the elevation drops 1' for every 10 linear feet).
If you wanted your rain garden to be 10" deep, you would dig 10" down into the ground at the top of the section, but by the time you reached the bottom you would actually be adding 2" of soil to make the base level.
Place the excess removed soil along the downhill edge of the rain garden so you can use it to build the berm (dam). , Depending on your soil, you may not need to add organic matter, but it can loosen the soil, enhancing its permeability and making it easier for new plants to develop strong roots.
It also makes for a better growing medium by providing nutrients that might be lacking in the soil.
If you choose to add organic matter, spread a 2-3" layer of compost in the bed of the rain garden and gently mix it into the soil. , Once you've dug the entire area out to the correct depth, "fine tune" your leveling either by eyeballing it or by taking a long 2x4 board and placing it on the ground with a carpenter's level atop it.
Fill in or dig out areas as necessary.
You just want to make sure you got rid of the slope and get out any major bumps or dips.
It doesn't have to be perfectly level, and you should try to avoid compacting the soil by walking around on it too much. , A rain garden can't do its job if water just flows out of it, so if there's any slope at all, you'll need to build a berm (an earthen dam) around the downhill edge and up the sides.
If you have leftover soil from digging, you can use this to make the berm, but for steeper slopes you'll most likely need to bring in additional soil.
An effective berm should be high enough so that it is level around the entire perimeter of the rain garden.
In other words, the top of the berm along the downhill edge of the rain garden should be at the same elevation as the uphill edge.
The berm should not be higher than the uphill edge, however, as this can cause the garden to retain too much water.
At the downhill edge of the slope, you'll probably need to add quite a bit of soil to make the berm high enough.
As you proceed uphill along the sides, the amount of soil required will become less and less until you reach the uphill edge of the rain garden, where the edge is high enough without any berm at all.
Shape the berm so that both the inside and outside edges have a gentle slope.
The berm should be rounded--you don't want to make a sharp vertical wall.
Compact the berm by tamping with a tamper or shovels.
The berm must be well compacted to prevent erosion. , It's best to choose native plants when possible, as they generally require the least care to thrive and also tend to develop strong root systems.
The plants in the rain garden itself should thrive in moist soil and be tolerant of influxes of large quantities of water.
It's a good idea to get plants that are at least 1-2 years old because they will already have established root systems.
A diverse blend of plants will require less maintenance, and you should try to incorporate native grasses or sedges (not turfgrass) into your garden.
Shrubs generally have excellent root systems that will soak up water and prevent erosion, and in larger rain gardens, you can even plant some varieties of water-loving trees.
Do some research to determine the best plants for your climate, but have fun and be creative. , A 2" layer of mulch will help keep weeds down and help your plants get off to a good start.
Be careful not to submerge the crowns of the new plants.
Heavier mulches, such as pine straw, wood chips, or shredded wood, are preferable to lighter mulches because the lighter materials tend to float and get displaced or carried away if overflow occurs.
It's generally a good idea to add another layer of mulch in the second year, but thereafter it should be unnecessary. , A ground cover or grass is essential to help reinforce the berm and prevent erosion.
It's also important at the top of the rain garden, where water flows in, because it slows down the water to prevent siltation and disturbance of the garden. , Care for the plants as you would care for other new transplants.
Make sure they get plenty of water, even when it doesn't rain.
After a couple years the plants will have deep, well-established root systems, and you probably won't need to water them except in the severest droughts. , As with any newly planted garden, weeds will likely be a problem.
Pull them regularly, and as your garden matures, your plants will eventually choke out the competition from weeds. -
Step 3: Plot out the garden plan.
-
Step 4: Stake out the garden area.
-
Step 5: Determine how deep your garden should be.
-
Step 6: Dig out the garden area to the desired depth.
-
Step 7: If the garden is in a level area
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Step 8: drive a stake at each end of the garden and run a string from one stake to the other
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Step 9: tying the string at the bottom of each stake so that the string is taut and touching (or almost touching) the ground over its entire length.
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Step 10: Add some compost.
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Step 11: Level the bottom of your basin.
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Step 12: Build a berm to hold the water in.
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Step 13: Plant an assortment of perennial plants in the garden.
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Step 14: Add a layer of mulch.
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Step 15: Plant a ground cover or grass on the berm.
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Step 16: Water the plants.
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Step 17: Control weeds.
Detailed Guide
It's easiest to install a rain garden in an area of your yard that water already flows to or through.
Your end goal is to reduce runoff.
You can usually identify a suitable area by examining your yard during a rain storm to see how water flows off it.
Rain gardens should be located at least 10 feet (3.0Â m) away from foundations to prevent basement flooding and structural problems.
They should never be located directly over a septic system, over underground utility lines--always call before you dig--or in a right-of-way.
In addition, rain gardens are not suitable for areas where the seasonal high water table level is less than 24" from the surface, as the water table will prevent infiltration of runoff water into the soil.
Finally, large rain gardens, or any rain garden that requires extensive excavation, should generally not be placed under large trees, as excavation may damage tree roots and excessive water can be harmful to some species of trees.
The more level the spot, the easier it will be to install your rain garden.
The rain garden site doesn't have to be perfectly level, but steeper slopes will require more excavation to make your garden deep enough to hold water, and slopes over 12% generally require too much excavation to be worthwhile.
A spot at the base of a steep slope is best.
Seemingly, the most obvious spot for a rain garden is a depression that already exists in your yard.
However, pooling or ponding may indicate that the water table is too high or, more commonly, that the soil has a low infiltration rate, which will make the area unsuitable for a rain garden.
To test for adequate drainage, dig a hole 6-8" deep and fill it with water.
The water should drain completely within 12 hours; if it doesn't, the spot is not suitable for a rain garden unless you do some extra work to prepare the soil (see Tips section below).
You are best suited to find a location that is suitable and redirect existing downspouts to it.
The ideal size of your rain garden depends on the size of the area that drains into it and the soil in the rain garden.
Determine the area (in square feet or square meters) of the surface that will drain into your rain garden.
Watch the drainage pattern during a storm or carefully examine the contours of your yard to determine where the water will come from.
Then measure this, including, if applicable, the area of your roof and any paved surfaces that will drain into the garden.
The area of your rain garden should be proportional to the area it drains.
For sandy soils, the rain garden size should equal about 10-20% of the total drainage area, while for very clayey soils, aim to make your rain garden equal to 50-60% of the total drainage area.
Loamy soils require a rain garden area somewhere in between these two extremes, depending on their clay content.
These proportions can be reduced for deeper rain gardens (those which are more than 5" deep over most of their area) or those that are more than 30 feet (9.1Â m) from the primary sources of drainage.
All these numbers, however, are only guidelines.
A rain garden can't be "too big," and even if it's smaller than the guidelines recommend, it will still help reduce runoff. , It's a good idea to plan your rain garden on a sheet of graph paper or a computer design program before you start digging.
Keep in mind that rain gardens typically work best if they are curved and slightly irregularly shaped.
The longest side should be perpendicular to the slope. , With plan in hand, use stakes and string (or hose) to mark the perimeter of the rain garden. , The ideal depth for a rain garden depends on the slope of the garden area.
A flat area or one with a very gentle slope can be as little as 3-5" deep, while 6-7" works best for a 5-7% slope, and 8-10" works best for an 8-12% slope.
Add another inch or two if you plan to incorporate compost into the rain garden soil.
Excavating deeper is recommended, typically 16-24" down., It's important to get the bottom of the rain garden as level as possible so that runoff water will spread evenly in the garden rather than pooling in one area.
To ensure that it's level, use the following methods, working in one 5-foot wide section at a time. , Dig the entire area to the same depth, frequently measuring the depth from the string to the base of what will be the rain garden.
If the rain garden is situated on a slope, you will need to dig the uphill end out deeper than the downhill end to ensure the base is level.
Drive a stake at the uphill end and another at the downhill end.
Tie a string around the base of the uphill stake, and then run the other end of the string to the downhill stake.
Tie the string to the downhill stake so that the string is level over its entire length.
You can attach a line level to the string to check that it's level, or you can use a standard carpenter's level.
Start at the uphill end and dig down from the string to the desired depth.
The amount of soil you actually need to remove will be less and less as you move farther downhill, and you may even need to fill in the bottom (downhill portion) of the garden with some of the soil you removed from the top (uphill portion).
As an example, suppose you had a 10' long section of your rain garden with a 10% slope (meaning that the elevation drops 1' for every 10 linear feet).
If you wanted your rain garden to be 10" deep, you would dig 10" down into the ground at the top of the section, but by the time you reached the bottom you would actually be adding 2" of soil to make the base level.
Place the excess removed soil along the downhill edge of the rain garden so you can use it to build the berm (dam). , Depending on your soil, you may not need to add organic matter, but it can loosen the soil, enhancing its permeability and making it easier for new plants to develop strong roots.
It also makes for a better growing medium by providing nutrients that might be lacking in the soil.
If you choose to add organic matter, spread a 2-3" layer of compost in the bed of the rain garden and gently mix it into the soil. , Once you've dug the entire area out to the correct depth, "fine tune" your leveling either by eyeballing it or by taking a long 2x4 board and placing it on the ground with a carpenter's level atop it.
Fill in or dig out areas as necessary.
You just want to make sure you got rid of the slope and get out any major bumps or dips.
It doesn't have to be perfectly level, and you should try to avoid compacting the soil by walking around on it too much. , A rain garden can't do its job if water just flows out of it, so if there's any slope at all, you'll need to build a berm (an earthen dam) around the downhill edge and up the sides.
If you have leftover soil from digging, you can use this to make the berm, but for steeper slopes you'll most likely need to bring in additional soil.
An effective berm should be high enough so that it is level around the entire perimeter of the rain garden.
In other words, the top of the berm along the downhill edge of the rain garden should be at the same elevation as the uphill edge.
The berm should not be higher than the uphill edge, however, as this can cause the garden to retain too much water.
At the downhill edge of the slope, you'll probably need to add quite a bit of soil to make the berm high enough.
As you proceed uphill along the sides, the amount of soil required will become less and less until you reach the uphill edge of the rain garden, where the edge is high enough without any berm at all.
Shape the berm so that both the inside and outside edges have a gentle slope.
The berm should be rounded--you don't want to make a sharp vertical wall.
Compact the berm by tamping with a tamper or shovels.
The berm must be well compacted to prevent erosion. , It's best to choose native plants when possible, as they generally require the least care to thrive and also tend to develop strong root systems.
The plants in the rain garden itself should thrive in moist soil and be tolerant of influxes of large quantities of water.
It's a good idea to get plants that are at least 1-2 years old because they will already have established root systems.
A diverse blend of plants will require less maintenance, and you should try to incorporate native grasses or sedges (not turfgrass) into your garden.
Shrubs generally have excellent root systems that will soak up water and prevent erosion, and in larger rain gardens, you can even plant some varieties of water-loving trees.
Do some research to determine the best plants for your climate, but have fun and be creative. , A 2" layer of mulch will help keep weeds down and help your plants get off to a good start.
Be careful not to submerge the crowns of the new plants.
Heavier mulches, such as pine straw, wood chips, or shredded wood, are preferable to lighter mulches because the lighter materials tend to float and get displaced or carried away if overflow occurs.
It's generally a good idea to add another layer of mulch in the second year, but thereafter it should be unnecessary. , A ground cover or grass is essential to help reinforce the berm and prevent erosion.
It's also important at the top of the rain garden, where water flows in, because it slows down the water to prevent siltation and disturbance of the garden. , Care for the plants as you would care for other new transplants.
Make sure they get plenty of water, even when it doesn't rain.
After a couple years the plants will have deep, well-established root systems, and you probably won't need to water them except in the severest droughts. , As with any newly planted garden, weeds will likely be a problem.
Pull them regularly, and as your garden matures, your plants will eventually choke out the competition from weeds.
About the Author
Judith Davis
Judith Davis specializes in lifestyle and practical guides and has been creating helpful content for over 2 years. Judith is committed to helping readers learn new skills and improve their lives.
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