In the past 5 years, the Chisago Soil and Water Conservation District has assisted in installing nearly 50 rain gardens around Chisago County.  As we continue to work on new projects, we occasionally run into misconceptions about rain gardens.  There are some common myths that we can dispel easily, and then there are new things we are learning with every project that help make future rain gardens even better.
Myth #1: Rain Gardens are Ponds
Rain gardens are designed to drain and dry out within 24 to 48 hours of the rain event.  They are simply a temporary ponding place for stormwater runoff during the actual storm.  Then the water drains away into the groundwater or through an underdrain tile to a stable outlet.  Through this process, the water is cleaned of excess nutrients such as phosphorus and other pollutants.  Therefore, the water reaching the groundwater or outlet is clean water.
Myth #2: Rain Gardens Breed Mosquitoes
Since water will not be standing in the garden more than 48 hours at the most, mosquitoes won’t have enough time to lay eggs and hatch.  Depending on the species, mosquitoes require 5-7 days to hatch.  Eggs that are laid in the rain garden while it’s full will not stay moist enough to hatch; therefore, rain gardens do not contribute to the mosquito population.
Myth #3: Native Plants are Messy and Weedy Looking
This can be true in some plantings, but we strive to make the rain gardens in public locations look well maintained and purposeful, like a regular perennial garden.  Native plants are preferred for rain gardens because they can handle the wet-dry cycle that happens as rain gardens fill up and dry out.  They also have very long roots that aid in water infiltration.  However, some natives tend to spread, can be large, and can look messy.  To avoid this, we use some cultivars that have been selected to be smaller or spread less.  We also use some common garden perennials, such as daylilies, that can handle the conditions.  With the correct design and plant selection, a rain garden with native plants can look just as manicured and formal as a regular perennial garden.
Myth #4: Rain Gardens Keep Water from Reaching the Lakes
With the water levels so low around the Chisago Lakes area, this is a common misconception.  The rain gardens do intercept water before it reaches the catch basin, which is piped directly to a lake or stream.  However, most of our rain gardens have underdrain pipes in them.  This is due to the heavy clay soils around the area that prevent infiltration.  Water filters through the soil and then leaves through the pipe, which is connected to the storm drain.  In effect, the water is just slowing down and being cleaned before reaching the same destination it previously had.  In locations where soil is sandy and an underdrain pipe isn’t needed, the water infiltrates into the groundwater.  Most of our lakes are groundwater fed, so although it may take a bit longer for the water to get there, rain gardens do not deplete the lakes of water.