The marginal winter pastures of reindeer and caribou (Rangifer tarandus) in Arctic and sub-Arctic areas are assumed to be nitrogen- and mineral-poor. Reindeer eat a mixed diet consisting of nitrogen-deficient lichens and a wide variety of vascular plants in winter. Some reindeer populations manage to maintain carcass mass outside the growing season and very little is known about the ability of reindeer to utilize vascular plants in this season. The chemical composition and in vitro digestibility of 17 species of vascular forage plants and one species of moss collected mid-winter from beneath the snow at an inland winter pasture in northern Norway were determined. Wintergreen parts of graminoids had a high content of crude protein (0.072–0.108 g/kg dry matter (DM)) and water-soluble carbohydrates (0.098–0.167 g/kg DM) and were highly digestible (50–65% IVDMD) compared with the withered parts of the plants (27–53% IVDMD). The digestibility of both shrubs and graminoids was inversely related to content of cellulose and lignin, but positively correlated with increasing contents of water-soluble carbohydrates. Shrubs were relatively calcium-rich (3.6–6.1 g/kg DM) while wintergreen graminoids contained up to 10.0 g/kg DM of potassium, 1.5 g/kg DM magnesium and 2.1 g/kg DM phosphorus. The present study demonstrates that the wintergreen parts of several species of vascular plants are nutritious, containing high levels of nitrogen and minerals, and that they are highly digestible to reindeer in winter. Vascular plants may, therefore, be more important to reindeer and caribou in winter than previously realized.