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Bring On the Rain (Gardens)

November 1, 2008

the seasons: spring, originally uploaded by -sel.

With the steady rise of urbanization more and more stormwater runoff is flowing unchecked into surface water and storm drains. Becuase the water can’t slowly seep into the ground and then flow naturally into groundwater it’s now causing erosion, water pollution, flooding, and diminished groundwater supplies.

Many people have blogged about rain barrels as a way to preserve this water for use in gardens but they can also protect our storm water systems from the sudden influx that accompanies rain. Another way to do that and increase the visual appeal of your house is a rain garden. It’s estimated that in comparison to a regular lawn a rain garden will absorb 30% more water. That water will go to plants and eventually soak into the groundwater supply instead of running rampant in a storm water system. Rain gardens also prevent pollutants like fertilizers, pesticides, oil etc from getting into streams and lakes. Once there it can cause untold damage and even if it is routed to a treatment plant we then have to pay for that water to be cleaned. It’s a completely unnecessary process when the water could be filtered through the ground the way nature intended.

Some common concerns about rain gardens are pests, standing water, cost, and maintenance. Because most rain gardens are designed to capture water and filter it into the ground the water won’t stand there long enough for pests to be a problem. The water will form a pond but it will only last a couple of hours. In addition to that rain gardens provide a great habitat for beneficial birds and insects that will eat mosquitoes. The gardens should be made from native species so you don’t have to go out and break the bank and may even be able to relocate plants from your existing yard and garden. Once established the garden will require some weeding and watering for the first two years and after that some thinning to prevent excessive growth. If you and your neighbors help each other out you could create multiple gardens in weekend, it’s a great way to get free labor 🙂 and build a sense of community.

There are some practical considerations as well aesthetic ones to keep in mind when deciding where to place your rain garden. The largest source of rain water is going to be from your roof so a location to capture roof runoff is a great start. You may also want to place a rain garden in order to capture excessive runoff from your roof and lawn. But keep in mind you don’t want to place a rain garden where ponds naturally form. If you get puddles thats an indication that infiltration is slow in that area and the point of a rain garden is increased infiltration. With this in mind you wouldn’t want to place the rain garden in full shade. Full or partial sunlight will help with evaporation and infiltration so the water doesn’t stand too long. You also want to avoid putting the rain garden within 10 feet of your foundation. Practicalities aside you want to place your rain garden where it can be enjoyed from inside and out.

The size of your rain garden will depend on the amount of runoff you are looking to control. If you are using it in concert with rain barrels then the garden can be smaller. Generally speaking you want your rain garden to be about 4-8 inches deep. If it’s too deep then you will get pooling that doesn’t go away and if it’s to shallow it won’t capture and infiltrate as much water. Another related consideration is your type of soil, sandy soils have the fastest infiltration and clayey soil have the slowest. Keep this in mind when designing the depth and size of your garden.

Hopefully I’ve sparked your interest! Rain gardens are excellent way to deal with rain and help return to a more natural system of water treatment and replenishment. They can be relatively low cost, easy maintenance and yet still have a big impact. An individual rain garden won’t save the world but if everyone in your neighborhood did it and you lobby for your town to get into like the city of Portland Green Streets Program you would see a huge difference. Not only would it greatly improve water management but these gardens and greenways add huge visual appeal in what is now a concrete jungle.

If you are looking for more technical advice on implementing a rain garden this is a great resource. It discusses in depth choosing a location, tools, resources need etc. Since it’s tailored to home rain gardens just about any question you can think of is answered.

Has anyone is installed a rain garden? What are your thoughts about it?

2 Comments leave one →
  1. November 1, 2008 2:15 pm

    Also having a gravel driveway will help. We toyed with the idea of paving ours, but decided to leave it graveled for that reason (not to mention we’ll be saving $15,000).


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