Green Heron Pond is one of the southernmost glacial potholes - an area where a large chunk of glacial ice remained (probably under the ground surface for many years) before it finally melted. A portion of the pond contains a small bog. The unusual aspect of this particular bog (a bog is a wetland type that accumulates acidic peat, a deposit of dead plant material) is that it still harbors living (peat) moss. Sphagnum needs a low pH to grow and the pH of soils on the Arboretum grounds is 7.5-8.0 (sphagnum needs 5.0 or under). How it has survived for thousands of years is one of life's perplexing questions!
First created over 40 years ago, the trail around Green Heron Pond rapidly became a well-loved favorite for generations of Arboretum visitors. The pond, its adjacent marsh and bog represent three naturally occurring ecosystems in Minnesota that are part of the state's geologic and landscape heritage. Just a half-mile long, the bog trail passes through the most diverse ecotypes of any Arboretum hike. Oak woods, maple woods and the mosaic of intermingled wetlands along the boardwalk offer rich rewards for birders, school groups and families. In fact, it's an “off the beaten track” nature experience that's easily accessible to the gardens and parking.
The boardwalk was closed for renovation in 2009. Now it’s back in service and better than ever with 100 new pilings - some to a depth of 60 feet. New interpretive signs will tell the stories of its green heron namesake and other wild residents, the lady's slipper orchids at the boardwalk entry and the tamarack bog, shrub swamp and cattail marsh that line the way. In the middle of this remnant glacial bog, it was fascinating to discover trees actually growing on a 10-12-ft thick mat of old roots, with open water beneath them. Visitors can enjoy the bog through the seasons from spring's yellow marsh marigolds to the golden tamaracks in fall.