Rain gardens not only absorb and filter storm water in the summer; recent studies have shown that rain gardens that are properly constructed and function effectively during summer months will also infiltrate water in the winter. 

Rain Gardens in Minnesota typically feature native plants, which are well adapted to our winters. While the above ground plants may look brown and dead, woody plants continue to photosynthesize any time tempetures are above freezing and below the ground the roots are alive, and feeding off of energy stored in the summer and fall. These roots systems help to maintain porosity in the soil below ground, which allows water to permeate even when the ground is frozen.

Of course, the plant roots are not the only reason that rain gardens function even in the cold. Organic soil amendments such as carbon rich compost freeze much more slowly than do sandy soils. This is due to the energy created by ion exchange during the decomposition process, which creates heat. Organic soils will often stay pliable well after pure sandy soils have frozen solid, which, when combined with native root systems allow for extended functionality. Of course, periods of extended sub freezing temperatures will eventually freeze even organic soils, but the time frame of impermeability is much shorter. 

As with all rain gardens, site specific construction is important.  Filter strips or sediment traps must be utilized to prevent sediment from entering and plugging the raingarden, and salt tolerant species of plants should be used in areas likely to receive runoff from sidewalks or parking lots where salt use during the winter is likely. Salt use can also be eliminated altogether if permeable pavement materials are used instead of standard concrete or asphalt for driving or walking surfaces.

Lakes Area Clean Waters Council
email us at: info@dropstopabsorb.org