Seedlings of Salix eriocephala Michx., Salix sericea Marsh., and their F1 hybrids were tested for their growth under contrasting water conditions. One-year old seedlings were grown in pots and subjected to one of two experiments, a scheduled-watering experiment (watered every 1, 4, 8, or 12 days) or a dry-down experiment (no watering after an initial period without water limitation). In the scheduled-watering experiment, short-term growth of hybrids was suppressed relative to the parents. However, subsequent watering allowed hybrids to recover. By the end of the 48-day experiments, hybrids exhibited heterosis across all treatments. In the dry-down experiment, hybrids again were highly susceptible to the onset of drought conditions. From these results, we hypothesize that temporal and spatial variability in water availability could determine the survivorship of hybrids and the frequency of introgression; high water availability may enhance the relative performance of hybrids, while low water availability may limit hybrids.Key words: Salicaceae, willows, hybridization, water relations, performance, heterosis.