By Tony Heath, Project Engineer
Howdy! It’s been an exciting week here at the Red Oak Rain Garden. We’ve seen some rapid changes to our landscape, which include removing the berm, making preparations for the new sidewalk, starting to remove the old bike path, saying goodbye to our shrubs, and starting to remove rock.
The Facilities & Services operators removed concrete from the bike rack area in the northwest corner and started removing shrubs, plant material, and rocks. During rock removal, the excavator snagged on a 3″ root of the London Plane Tree. After consulting with Brent Lewis, Campus Landscape Architect with Facilities & Services, we cut the damaged area with a saws-all to provide a clean edge (rather than a tear), covered it with topsoil, and placed white flags to mark the root location. Should further excavation be necessary in this area, we will use an air spade, which is specialized equipment.
The health of the other tree, the Red Oak, is also important to us, not only because it’s the namesake of the garden. This week, we spoke with Ryan Pankau, Champaign County Extension, and Greg Smith, Arborsmith, as well as Diane Plewa at the University of Illinois Plant Clinic on how we can best maintain the health of the tree.
Rain Gardens typically have soil amendments to help with infiltration. We are revisiting our soil amendment plan after consultation with Thomas Rainer, Registered Landscape Architect at Phyto Studio, Tony Endress, NRES Professor Emeritus, and Greg Smith, Arborsmith. Originally, our plan was to add a sand/compost mix in the north cell. Instead, we will simply backfill with native topsoil and apply mycorrhizal inoculant before covering with mulch. There are some areas that have been heavily compacted, such as under existing concrete and in the gravel channel. We’ll relieve that compaction by ripping the subsoil to a depth of 18″ and backfilling with the native topsoil. In the south cell, we’ll be using a sandy soil mix to create a leaner growing environment, discourage weed growth, and improve infiltration. We’ll be following the Minnesota Stormwater Manual design specification, which calls for 60-70% sand, 15-25% topsoil, and 15-25% compost.
Lastly, we bid a fond goodbye to the shrubs. Although they were overgrown and deemed not worth salvaging, they served our ecosystem well for many years and for this we thank them.
Looking forward to next week, where we will continue removing rock and begin installing the new sidewalks.