The stems of cut greenhouse roses, Rosa hybrida ‘Samantha’, were fully hydrated and then allowed to dehydrate while measurements were made of water loss, stem water potential, hydraulic conductance and the onset and extent of xylem cavitation (i.e. disruption of xylem water continuity). The inter-relationships of these parameters were followed through the full range of plant water status. Xylem cavitation was initiated at stem water potentials of −0.2 to −0.4 MPa. Rates of cavitation increased as water potential declined. This was associated with a corresponding decline in stem hydraulic conductance. The data indicated that a loss of about 50% of the stem water content at full hydration resulted in a total loss of water-conducting capacity. This corresponded with a stem water potential of about −4.0 MPa. The results indicate that the shelf-life of a cut flower may, in many instances, be relative to the proportion of functional xylem remaining in the stem.