Interested in taking your rainwater harvesting to the next level? Creating a rain garden in your yard may be something you’d consider. Rain gardens are easy to build and offer an attractive way to allow stormwater to percolate into underground aquifers, which will help create a more environmentally sustainable Los Angeles.

 

If a rain garden sounds like a winter DIY project you’d like to tackle, read on to learn more about rain gardens and their benefits, as well as the steps you’ll need to take and materials you’ll need to “grow” your rain garden. 

 

What is a Rain Garden?

A rain garden is a small depression, which is usually formed on a natural slope, and planted with native shrubs, flowers and perennials. 

 

Why Create a Rain Garden?

Rain gardens have many benefits! For you and your family, switching up your landscaping to include a rain garden can be a fun project that yields a beautiful addition to the yard. Beyond that, key environmental benefits include: 

 

  • Cleaner Water: Rain gardens help keep our waterways clean by filtering out sediments and other pollutants via plant roots and soils. Additionally, rain gardens slow the flow of runoff, which would otherwise make its way onto sidewalks and roadways, pick up contaminants, and enter our storm drains.
  • Water Conservation: Rain gardens capture and store water, allowing it to slowly soak into the ground. This means that rain gardens rarely need to be watered! Plus, any additional water that isn’t absorbed by your native plants will filter down into underground aquifers.
  • Habitat Creation: Native plants in your rain garden support a variety of beautiful birds, butterflies, beneficial insects, and other wildlife by providing food and shelter. 

 

The LA Department of Water and Power as well as many other water districts, offer residential rebates, such as for turf replacement, which you could weave into your new rain garden design.

 

 

Steps For Setting Up A Rain Garden:

 

 

1. Assess Potential Sites

The main goal of selecting a site for your rain garden is making sure it’s in a good area where it can intercept and collect rain runoff. Some good options are down slope of a downspout or adjacent to an impervious surface, like your driveway. 

 

  • DO build your rain garden in an area that is:
    • Relatively flat 
    • Naturally low lying with good drainage
    • Away from your home
  • DON’T build your rain garden:
    • In an area with existing tree canopy cover
    • Above septic systems
    • Where potential overflow will run onto neighboring properties. 

 

If you have concerns regarding underground utilities on your property, always be sure to call 811 prior to siting your rain garden and before you begin to dig. 

 

 

2. Design Your Rain Garden

Once you’ve decided on your rain garden’s location, the next step is determining its area and depth. However, if you don’t have a ton of space in the yard or don’t want to commit to a larger project, remember that even a small rain garden can be incredibly effective. 

 

How deep should my rain garden be?

 

Rain gardens can be anywhere from just a few inches to a couple feet deep! The best way to decide how deep to dig is to know your soil. 

 

  • If your yard has sandy soil: it will drain relatively quickly and you can create a deeper ponding area. 12” (1 foot) deep will work well.
  • If your soil is closer to clay: you’ll want to make sure you stop your digging on the shallower side, around 6”, to avoid water standing for longer than 48 hours. 

 

How big should my rain garden be?

 

1. Once you’ve decided how deep your rain garden will be, you’ll first want to gauge the square footage of the roof section, driveway, or other surface that will divert rainwater into your rain garden. 

2. From there, multiply the area of runoff by 1/12th of a foot (or 0.08333). This will give you the volume of water (in cubic feet) your rain garden will hold from a 1” rain event. 

3. Now that you have the volume of your rain garden, divide that number by the depth you decided on – either 1’ or 0.5’. This will give you the square footage of your rain garden.

4. Once you have the square footage, choose the dimensions based on the available space, conditions of your site, and personal preference. Oval or kidney shaped rain gardens are common, but any shape will do!

 

If you’d like to account for more factors or if math just isn’t really your thing, the Three Rivers Rain Garden Alliance Calculator is a great resource to help you size your rain garden.

 

3. Setup & Materials

Now that you know where your rain garden will go, how deep it will be, and how big it will take, let’s get into the actual setup and the materials you’ll need!

 

In general, your rain garden will have an inflow pathway (e.g. a downspout from your home or a small rock-lined path to guide water), gradual side slopes into the ponding area, and raised berms. You can also choose to include an overflow path to direct any excess water into other areas of the yard.

 

For the Ponding Area:

a) First you will need a mix of drainage rock and gravel for the bottom of the ponding area (i.e., the area you’ll be digging out). This will allow for water flow into bottom soil layers.

b) Next you will want a mix of soil and sand above your first layer to help soak in water while also allowing it to infiltrate down through the layers. 

c) Lastly, place some river rocks on top. This will help rainwater to evenly spread out over your rain garden and allow for ponding.

 

On the sides of your rain garden, you’ll want to create slightly raised sloped mounds of soil (also called berms) to help contain the rainwater and prevent overflow. The soil you dug out to create the depression will work perfectly as berms. They can be covered with mulch once they’re in place. 

 

4. What should I plant in my rain garden?

Stick to native and drought tolerant plants – these plants will require minimal supplemental irrigation in the dry season. Additionally, have fun with diversifying your garden. Not only will this help make your garden aesthetically pleasing, but also will attract a variety of birds, pollinators, and other beneficial insects!

 

If you’re not sure where to start with native plants, check out the California Native Plant Society for guidance. The Theodore Payne Foundation, located in Sun Valley, is another great resource for native plants and gardeners. 

 

5. Building Your Rain Garden

a) Outline the garden with string and stakes

b) Prep the ground: If the soil is too hard to dig, moisten it with a garden hose and allow the water to seep in overnight. You’ll need to dig out any plants or grasses, but be sure to save any natives that can be replanted!

c) Dig out your rain garden, but be sure to create a slope of at least 20 degrees to help guide rainwater into it. 

d) Amend your soil with compost as needed and add in your native plants and mulch. 

 

If you would like to learn more about rain gardens and other ways you can harvest rainwater at home, check out this resource from the City of Los Angeles’  Rainwater Harvesting Program! 

 

And once you are done, we would love to see your beautiful rain garden! Feel free to email photos to us at lastormwater@lacity.org.