Why rain gardens make sense
A simple sketch of a system to hold onto what falls from the clouds.
Flower garden, rain garden, rose garden, veggie garden. Whoa! Back up! We can picture most of these but what the Hello Dolly is a rain garden? No long, winding, slightly incoherent intro today (sorry!). I’m just going to give you the elevator pitch on rain gardens. I know. You’re thinking, “Hey Gar, it’s winter. Why are you talking about rain?” For one, most of you reading this (Yes, you two!) live in Tennessee where rain is much more likely to fall from the sky than the white stuff. Secondly, we sometimes need to be reminded how precious water is and think of ways to hold on to it as long as possible, especially now that it happens so less frequently.
A rain garden is a term given to a place in your garden/on your property that collects rain. Ta-da! Thank you. You’ve been a great audience! Seriously, there is just a bit more to this story so buckle in.
In the days of old, the consensus regarding rain was out of sight, out of mind. This is still the prevailing thought for most engineers and designers of stormwater systems. Put it in a pipe as quickly as possible, say a prayer, and dump it into the nearest stream. Fortunately, our mindset is slowly changing, thanks to ecologists, landscape architects, and other like-minded, tree huggers.
Clean, drinkable water, which makes up just 1% of the world’s water supply, is our most valuable resource. 23% of this is used for irrigation (46% in the west, where they think it’s still fun to grow grass and play golf in the desert). Yes, I know flooding can be catastrophic and our own basement can attest to the property damage that comes from biblical rains but I also get a bit stressed when we go for 3 or 4 months without a drop from the sky so when it does fall, I want to hoard my fair share.
Our rain barrel complete with a nifty “Y” diverter to toggle flow to bypass when the barrel is full.
Rain gardens are not ponds. They are meant to hold only the first inch or so of rain (which accounts for most of our rain events in my area). The depth is usually less than 12”. Depending on your soil (clay, sand, loam) the percolation rate of the collected rainwater will vary. Sandy soils = you’ll never see the water. Clay = water will take a while to move downward. You can see more of the profile of a rain garden in the sketch at the top.
Location – Choosing a spot for your rain garden can be somewhat limited. It won’t likely be the high point of your property. See where your downspouts from the gutters are located and go from there. You may need to extend or add pipe. I recommend using 4” PVC drain pipe (it doesn’t need to be pressure-rated since it’s not holding any water). Don’t use the corrugated, black flexible pipe if you have taller trees around or no gutter protection. These will always clog and fail over time. You might find that a little redesign of your garden is required to make this new addition appear to be part of the larger picture.
Size – Near the end of this writing is a sketch by British landscape architect, Nigel Dunnett, showing how a rain garden can be just one piece of a large stormwater management puzzle. In his and co-author, Andy Clayden’s book, there are formulas for how large to consider making your rain garden. This takes into account your soil type (clay vs sand vs loam). While the percolation rate of your soil does matter, don’t overthink this.
Just carve out a wide, shallow (maybe 12”) dish-like hole that doesn’t eat up all your outdoor living space and fits the scale of other features in your garden. Also, look at where the rainwater will travel once your rain garden is full and plan for that to happen. For ours, I installed a smaller diameter length of drainpipe just under a nearby path and let this “daylight” or emerge from the ground where the slope allowed.
One thing I would recommend not doing that may seem logical is using an underlying geo-textile or weed fabric beneath the rock. While some may believe this will keep out weeds (it won’t) or keep the stones from migrating downward into the soil, that stuff is just nasty and belongs only under fine, level, gravel paths. The problem is that this fabric will eventually become caked with silt or other fine debris and you won’t get the natural percolation of the rain that you want. See one of my older posts for more: https://garrymenendez.com/weed-fabric/
Planting – Adding a few plants will transform and soften your rain garden. How many is up to you. When choosing plants look for the word “adaptable” with regard to water needs. This means these plants should be able to handle long periods of dry conditions as well as having their root systems submerged for several hours or even days. Perennials are your best bet since you really don’t want shrubs or trees in this garden. Some of my favorites include: iris, little bluestem, goldenrod, spiderwort, Joe pye weed, cardinal flower, threadleaf bluestar, and swamp milkweed.
Our rain garden early on. A pipe collects water from the nearby garage, runs under the patio, and outflows into the garden.
Beyond rain gardens, there are other things you may consider to make your property more sponge-like. If you’re building a new home, consider minimizing the amount of impervious surfaces (traditional concrete and asphalt) and use pervious materials instead. While the materials (paver blocks) themselves may not be pervious, these systems are designed to allow water to filter between the joints and then percolate through the base and eventually into the water table. Since I’m getting off subject here be on the lookout for more about this in a future post.
Here’s a great book on the subject and a sketch from within:
A sketch from the book shows how a rain garden can be part of a larger system.
OK, that should be enough to think about for now.
Till next time,
HOLD ON TO THAT RAIN!
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