The timing and availability of water supply is changing in the Okanagan Valley, and the availability of irrigation water in the late summers is a growing concern. Postharvest deficit irrigation (PDI) is a strategy that can be used to reduce water demands in sweet cherry orchards; previous studies in this region have reported no change in plant physiology or tree growth with irrigation volume reductions of up to 25 %, postharvest. However, the effects of more severe postharvest reductions in irrigation volume remain unknown. We compared the effects of full irrigation (100 % of conventional grower practice through the growing season) with 27-33 % reductions in irrigation postharvest (~70 % of conventional grower practice) and 47-52 % reductions in irrigation postharvest (~50 % of conventional grower practice) over a three-year period (2019-2021) in five commercial sweet cherry orchards that ranged in elevation and latitude across the Okanagan Valley, BC, Canada. In the growing season following treatment application, PDI had no effect on stem water potential or photosynthesis in any year and at any site; there were also no effects of PDI treatment on tree growth. Findings from this study suggest that postharvest stem water potentials from -0.5 MPa to -1.3 MPa, and one-time stem water potentials as low as -2.0 MPa, have no lasting effects on future plant water status, rates of photosynthesis or plant growth. Postharvest deficit irrigation shows potential as an effective water-saving measure in sweet cherry orchards in the Okanagan Valley.

Irrigated agriculture in semi-arid regions is expected to increase in the future, which puts greater demands on scarce water resources. Sustainable irrigation strategies in semi-arid regions will support agricultural resilience to climatic change. The response of ‘Sweetheart’/Mazzard sweet cherry trees (Prunus avium L.) to postharvest deficit irrigation (PDI), as a water conservation method, was studied over three seasons (2019-2022) in the semi-arid Okanagan Valley of British Columbia, at five commercial orchards. The following irrigation treatments were applied; (i) a control of full irrigation, irrigated according to conventional growers’ practice at each orchard, (ii) PDI-30 - 27-33 % reduction in irrigation volume, after harvest (67-73 % of control) and (iii) PDI-50 - 47-52 % reduction in irrigation volume, after harvest (48-53 % of control). Spring phenology (the timing of flower bud development, from side green to full bloom), flower bud moisture content and cold hardiness, and fruit yield and quality (before and after cold storage and shelf-life conditions) were assessed to determine if PDI altered fruit development over the subsequent growing season. Neither PDI-30 nor PDI-50 caused changes in the timing of flower bud phenology, cold hardiness or moisture content relative to the control. PDI treatments also had no effect on fruit yield or fruit quality at harvest or after storage and shelf-life conditions. These results suggest PDI could be used to reduce irrigation water use in semi-arid regions, like the Okanagan Valley, without affecting sweet cherry production or fruit quality.