Bryophyte growth is most often cited as being primarily water-limited; however, experimental manipulation of water availability in the field has not previously been employed to test this hypothesis. Here we follow the growth responses of a leafy liverwort, Bazzania trilobata, to field water addition treatments. Our study system was an eastern hemlock stand located in the lower Hubbard Brook Valley in northern New Hampshire where Bazzania forms pure colonies over boulders. The experimental design accounted for effects of boulder treatment (control, water addition or water plus nitrogen), aspect (north- or south-facing), position (top, east or west side of a boulder) and liverwort stem density. To follow growth responses of Bazzania, we tracked changes in biomass gain, stem elongation and branching over 86 days. Environmental measurements for the evaluation period and supplemental physiological data for Bazzania were also taken. An increase in water availability did not evoke a straightforward increase in growth. Water and water plus nitrogen additions appeared to have a short-term initial effect on biomass gain and a moderating effect on elongation and growth rates. Biomass gain of Bazzania stems appeared limited by respiration costs, but further evidence would be needed to confirm this hypothesis. Branching was favored over stem elongation in grid cells with fewer stems and positions receiving higher light intensities. A carbon-balance hypothesis, considering the water, light and temperature conditions required to achieve a positive carbon balance, offers a more realistic model of the complexity of limitations to bryophyte growth. Comparative ecology of carbon balance for mosses and liverworts offers an intriguing and under-explored avenue in bryophyte ecology.