A blue ash tree at night. Blue ash, Fraxinus quadrangulata, is common on limestone uplands throughout the midwest, especially in the Bluegrass. The tree is named for the blue dye that can be extracted from the inner bark. The species name refers to the twigs, which are square in cross-section.

Blue ash is a huge, stout tree larger than the other local ash species. My observations indicate that it is resistant to the emerald ash borer unless it is stressed. In one pasture with about 20 mature blue ash, only one succumbed to the emerald ash borer, and it had substantial lower stem damage from brush cutters.

Photo: Blue ash at sunset with a full moon. Photo by Tom Kimmerer