Retain the Rain to Grow a Resilient, Sustainable Garden
Why should you care about retaining your rainwater? It’s a water-wise way to create a sustainable and resilient garden, especially for those of us who live in California’s dry climate.
When it rains, all the water that isn’t absorbed into the ground runs off into storm drains or bypasses and flows directly into the nearest waterway. Creeks, marshes, and the Bay become polluted with chemicals, pet waste, motor oil, debris, and anything else the runoff picks up from the environment.
It’s important to be aware of your runoff responsibility and keep water on-site as much as possible. Your garden’s health and the entire ecosystem around it depends on retaining (and using) the rain that does come your way!
4 Key Benefits of Rain Retention
When you hold onto rainwater, this helps you grow a resilient and sustainable garden. Let’s dig into why being water-wise and retaining the rain matters.
1. Prevents pollution and runoff
Especially in the dry California climate, runoff is common during periods of excessive rain or rainfall after a drought. Keeping rainwater on-site prevents pollution in our creeks, wetlands, and the Bay. It also benefits your home and garden directly.
Retaining the rain with buckets, barrels, or a rain garden prevents flooding, runoff, and pollutants from getting swept up from sidewalks and streets into the storm drains. This runoff negatively affects not only your garden’s soil but also your water quality.
Let’s put it into perspective. In a vegetated area of nature, approximately 50% of rainwater soaks into the soil. In developed urban areas, it’s closer to 15%.
How deeply the water can be absorbed into the ground also matters. In urban areas, more rainwater runs off instead of soaking into the soil because there are less permeable surfaces.
Water is a powerful force that can displace soil and cause foundation and structural damage.
Even if rainwater stays on our property, without the proper structures or plans to retain it, it can lead to eroding foundations.
One way to reduce runoff is to help your soil absorb and retain more water. The two best ways to do this are by adding compost to the soil and top dressing with mulch. Compost turns your soil into a sponge. Amending your soil with just 5% compost quadruples the soil’s water holding capacity. Covering your soil with 2”-3” of mulch significantly reduces the water evaporation rate, locks in moisture, feeds the soil as it breaks down, insulates the soil, and reduces erosion.
2. Supports the health of your plants and garden
Collecting rainwater replenishes water in the soil and recharges the groundwater as it moves from the surface into the deeper soil. This helps to reverse the effects of water stress caused by climate change, population growth, and increased food demand.
3. Reduces your reliance on municipal water
The upfront investment in a rain catchment system might feel daunting, but it benefits your wallet and the environment long term. When you capture rainwater, you reduce your need for potable, municipal water to irrigate your garden. This helps the environment and saves you money!
4. Keeps flooding at bay
Rain retention keeps relatively clean water out of the sewage systems. It also reduces the volume and peak flows during heavy rains that can flood combined sewage systems.
Systems For Collecting Rainwater
Rainwater collection systems can be large or small, high-tech or quite simple. They can also be used for different purposes.
Some capture valuable rain runoff from your roof so you can use it throughout the winter to keep your spongy soil hydrated. Other systems are meant as storage for use in the dry season.
The purpose will impact which ways you choose to keep water on-site such as with:
Rain gardens
Cisterns and tanks
Rain barrels
Buckets
Considerations for Collection Systems
Once you choose the collection systems you want to retain the rain, there are a few considerations to help you decide where to put them.
Does your roof area drain to downspouts? Where do you want to release the water (since, in most cases, you want this water to irrigate your garden)? Have you checked the local permit requirements? What size barrels or cisterns are best for your property? Is there a flat, shady spot to install them? If you’re using large tanks, are they near a support wall so you can secure them with metal straps? Can the ground hold the weight of the barrels when they are full of water (8 pounds per gallon in a 50-gallon barrel is 400 lbs)? Does your overflow pipe have a screen to prevent insects, birds, or rodents from entering? How much water does your garden use during the dry months?
Remember: this is non-potable water, which is not intended to be reused as drinking water or indoor use.
Want to calculate the amount of water that comes off your roof per downspout to determine what size of rain garden you need? Here’s how: 1” of rain over a 100 sq ft surface, such as a section of your roof, captures 60 gallons of water.
The Function and Features of a Rain Garden
Rain gardens are landscaped areas designed to receive overflow from your catchment systems as well as rainwater runoff from your roof, sidewalk, patio, or other impermeable surface. They are aesthetically beautiful, relatively easy to install, and fairly inexpensive. Rain gardens are also great for the environment! They support pollinators and beneficial insects, moderate temperatures, and assist with carbon sequestration.
How do they do that? By allowing the water to stay on site instead of running off into the storm drains and gathering pollutants along the way. The idea is to slow the flow of water, spread the water out over a wider area, and allow it to sink in by nurturing healthy soil and deep-rooted plants.
Rain gardens help restore the natural balance in our landscapes by holding back and soaking that extra rainwater into the ground.
It’s recommended that the size of your rain garden is 4-10% of the contributing impervious surface area. Your soil type affects the size due to the water infiltration rate. The slower the infiltration rate, the larger and wider your rain garden needs to be.
Additional questions to ask yourself:
What are your non-potable water needs?
How much room do you have for barrels or tanks?
How much roof runoff can you capture?
How much annual rainfall do you anticipate?
Why Plant Selection Matters
Choosing the right plants for your rain garden – like flowers that are drought and rain-tolerant – helps prevent weeds and reduce runoff. Opt for regionally appropriate, native plants that thrive in wet winter conditions and dry summer conditions.
A few of my go-to's are California native poppies (Eschscholzia californica), yarrow (Achillea millefolium), California fescue (Festuca californica), toyon (Heteromeles arbutifolia), and redbud (Cercis occidentalis). Make sure to irrigate throughout the summer months until they are established to nurture deep root systems that reduce runoff.
Ways We Can Grow Together
If you want to learn how to install a rain garden or dig even deeper into the benefits of rainwater collection, you’ll love:
This webinar recording I presented on behalf of the OWOW program in partnership with the Solano Stormwater Alliance
My next upcoming in-person event about retaining the rain
Booking me for your next garden club, business group, organization, or lunch & learn event