Water Garden or a Rain Garden?

Rain Garden

Mother Nature sometimes seems cruel, don’t you think? The west coast is burning up and we’ve had so much rain, I’ve seen small ponds formed in meadows that simply haven’t gone away all summer. My muck boots are taking on a somewhat greyish pickled look. Well, like they say, if given lemons you might as well make lemonade, right?

Shortly after moving to my Dublin home and having most of the timber cleared off the property, I had a small pond dug where previously a pvc pipe from the house’s perimeter drain had just deposited runoff into the woods. I’ve many times been thankful for that drainage system that surrounds the house, but I also thought it seemed like an opportunity to do something with that water. A garden pond! The one sole benefit I can think of about Dublin’s heavy clay soil is that it absorbs water very slowly, so I didn’t need a liner for my pond. The excavator operator just made an eighteen-foot tapered bowl and the water stays in. That existing drain pipe fills the pond and on the other side, another buried pipe acts as an overflow and travels down the slope of the pond into the roadside ditch. What was once a sloping forest floor is now a sweeping lawn with a little pond I’ve planted winterberry, forsythia and various water-loving irises around. I made the mistake of introducing cattails which I fight to get rid of on a yearly basis.

The ground water here is dense with iron and consequently that reddish slimy bacteria forms when there’s no movement in the water, so I gave up on making it a koi pond. I actually tried a couple goldfish initially but the next morning they were belly up. Now, I just leave it for the frogs and salamanders that have since populated it. While the pond is attractive and adds a point of interest in the landscape, I recently realized that I’m not necessarily helping the environment much by having it. Not harming it per se but to quote a previous property’s insurance company addendum I once received, it would qualify as a “decorative nuisance.”

A truly beneficial use of runoff water is the concept of a rain garden. It’s scientifically known as a bioretention facility according to Wiki. It’s intended purpose is to catch polluted runoff and filter it naturally through the use of various plants and soil types. Regarding the use of the word polluted, we’re typically not talking about pollution in the general sense of oils, chemicals and garbage permeating water. It’s any water that that runs off an impervious surface such as rooftops, asphalt driveways, parking lots and even compacted, treated lawns. You might think that rainwater coming off your roof would be pretty darn pure, but it does flow across a petroleum-based surface before going down your gutter. A lawn, too, seems pretty innocent but a hard rain where water can’t instantly be absorbed runs off and carries traces of any fertilizer or weed defense chemical you may have treated it with.

The basic elements of a rain garden are a shallow bowl of sorts excavated into the ground surrounded by a slight berm to temporarily retain water. If the existing soil content does not allow for easy absorption of water, it should be replaced with a more permeable soil. Native plants and shrubs are then planted over the garden’s surface. The selection of plants should be done with three key elements in mind: deep rooted natives, wet tolerant as well as drought tolerant. The point of the project is to not have the garden filled with water for any length of time. The runoff enters and is quickly absorbed in the soil (with sometimes an under layer of gravel) and such is filtered into the natural groundwater ecosystem.

While the benefits of a rain garden is primarily all about filtering runoff water naturally, it also provides a great opportunity to plant flowering pollinator perennials which will also benefit bees, butterflies and other native plants within range as those insects travel about and pollinate.

Interestingly, the first rain gardens for residential use didn’t appear until around 1990. The closest older cousin would be our good old roadside ditches filled with native plants that also acts to filter the runoff from our lawns and driveways. So, while my garden pond might be a “decorative nuisance” in some folks eyes, it still is only sending overflow into one of the oldest school bioretention facilities there is.