Our city government is slowing going raingarden crazy. With the help of the Rock River coalitions Rain Garden in Every Community, we have at least 5 gardens up and running in our little hamlet-with many more to come. In this post I will do my thing: talk theory, give practical advice and pepper the post with links to a small fraction of the fantastic resources on the web to save you some time on Google.
WTH is a Raingarden?
The raingarden is any intentional planting to slow runoff and increase rainwater percolation into the aquifers. Runoff is a significant problem that goes hand in hand with Sprawl-we take good permeable soils from farmland and forests, and cover them with impervious surfaces like houses, concrete, and lawns (the average high % bluegrass lawn is so matted with roots and compacted that it has almost as much runoff as concrete). This leads to significant problems with increased flooding in the short term and in the long term, those millions of gallons of water are flowing downstream instead of slowly filtering down to replenish our aquifers. Plus the environmental damage done by covering our impermeable lawns with more fertilizer and herbicides per acre than the worst industrial farm is immense. Those chemicals runoff into our streams and lakes where the fertilizer creates algae blooms and the herb/pesticides wreak havoc on the ecosystems and poison our waters. Raingardens planted along side driveways, slab porches, and
under downspouts halt this runoff and the light soils and deep roots of the perennials allow the water to trickle back into the earth. Our gardens, plus our rainbarrels hold 2500 gallons per event and once the plants are up it will be transparent to he casual observer-and pure eco-beauty to those in the know. Our small (6′ diameter) established raingarden waters birds, looks beautiful throughout the summer with varied bloom times, and this year hosted a monarch butterfly catepillar on the milkweed-all with zero human input after the construction!
Sweet! How do I build one?
Raingardens fall into two broad types: ‘planned’ gardens and engineered soil gardens. Both rely on an appropriately sized garden that is set into a depression 4-6″ lower than the surrounding ground to stop runoff and allow the water to percolate down. The planted rain garden relies on specially chosen plants (here’s a great list for the upper Midwest) that can handle both being submerged and temporary dry spells-and they sink roots down deep. How deep? A Purple Coneflower grows about 3-4′ tall, but will sink roots down 10-14′! Every day those roots expand and contract-creating zillions of small passageways for water to penetrate the earth. Most often these plants are native perennials and need no chemical fertilizer (compost is always welcome!) and very little additional water once established unless you are in severe drought. Engineered soil raingardens achieve the same percolation, but use more manual labor. Instead of digging the depression down 4″-go 18-36″ down, and then backfill with a mix of 25% sand, 25% Soil, and 50% Compost (very rough percentages are fine). Then plant the garden as you would any normal garden bed, or even lawn as long as it has a low (well under 50%) bluegrass mix, however the lawn will impede the percolation quite a bit.
Here are some great resources on Raingardens:
Wisconsin DNR-WI is raingarden crazy and their site is great!
The Raingarden Network-the name sums it up!
The Prairie Nursery-turn key native plant raingardens-for a price. Great place to generate ideas. PN supplied the plants for our larger raingarden, though I just picked my own based off plants in their garden mixes. Great people to work with.
Learnings from our gardens:
> Don’t skimp on the sedges and grasses-they are integral for soil stabilization and weed suppression a 1:1 ratio of sedges/grasses to flowering plants is ideal.
>Perk test your soil before you plant. Our first rain garden was a rain ‘pond’ due to a 3′ thick layer of clay under the topsoil. The roots will eventually break that up-but in the 3-4 years that would take we would have bred 16 million mosquitoes. Solution? I dug a 12″ wide hole 4′ deep with a post hole digger and filled it with compost. It nows drains in 2-3 days (ideal) and not 2-3 weeks (mosquito nursery). Perk tests are simple-dig an 18″ deep hole and fill it with water-if it drains more than 6″ in 24 hours your fine. If not, you need to engineer the soil or make the garden much broader and shallower to reduce standing water.
>Keep the gardens 10′ from your foundation to avoid seepage issues-you want the water in the well, not your basement! We just dig a slight swale leading from our rainbarrel overflows to the
gardens and line it with rock.
Finally-something is better than nothing. If you have a dense soil and don’t have space or money for a 500 sq ft garden-do what you can. Even modifying existing gardens by adding a slight external berm on the down side of a slope will have benefits that will literally begin to heal the Earth. Native plants are the best, but use what you have if need be-split your perennials and start a garden with what you have and can take the extra moisture.
We plant gardens to surround ourselves with nature’s beauty-with a Rain Garden you can also help heal the damage our race has done-and leave a better Earth for our children.
Be the Change.
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