Though large parts of the Arb were prairie at the time of European settlement, almost all of the prairie has been lost completely. This reflects the general condition of tallgrass prairie in Minnesota and in North America; by most estimates more than 99 percent of the tallgrass prairie in Minnesota was destroyed during European settlement. In the Arb, there are a few remnant prairie species along the Cannon River bluffs in the northeast corner of the Arb and along the railroad tracks near Waterford, but the best original prairie fragment is Postage Stamp Prairie in the Upper Arb (G4). And while not technically in the Arb, McKnight Prairie is the largest and most intact native prairie remnant owned by Carleton.
Large areas of tallgrass prairie are being restored in the Arb. It is much more difficult to restore prairie than to restore forest, both because most of the prairie plants are locally extinct and because the process of succession to prairie is extremely slow. Intense planting and care are necessary to grow a prairie that even begins to approach the diversity of the original community. The first step is to introduce the appropriate plant species one by one, either as seed or seedlings. Introduced plants are from local sources whenever possible, to ensure that genotypes are adapted to regional conditions. Once the restored prairies have begun to mature, they can be a valuable source of seeds of local plant genotypes for other nearby prairie restoration projects.
The first prairie restoration in the Arb was begun at Hillside Prairie (F10, G10-11) in 1978. New areas of prairie now are being planted annually in the Lower Arb, and the development of the prairie community is the subject of ongoing research by Carleton faculty and students. There ultimately will be about 140 acres (57 hectares) of restored prairie in this area of the Lower Arb.
In the Upper Arb, prairie restoration to date has been focused around Postage Stamp Prairie. There were plantings in 1989, 1990 (the Okada Garden), and the fall of 1992 (as part of the Wright Savanna, see below). These plantings have expanded the prairie area at this site by at least 10 times.