Microclimate mulching modifies date palm (Phoenix dactylifera L.) phenology and thermal requirements under seasonal climate variability

Date palm ( Phoenix dactylifera L.), a cornerstone of oasis agroecosystems, exhibits pronounced phenological sensitivity to climate; however, systematic evaluation of agronomic strategies to buffer this variability remains limited. This study assessed four mulching regimes: no mulch (NM), shredded date palm fronds (SDPF), black polyethylene plastic plus SDPF (PP+SDPF), and black polypropylene woven ground cover plus SDPF (PWGC+SDPF), to determine their effects on date palm phenology in two contrasting Moroccan seasons (2024 and 2025). Daily field observations tracked spathe phases (Phase A: dormancy break to emergence; Phase B: emergence to opening; Phase C: opening to pollination), phase-specific thermal time, base temperature, growing degree days (GDD), and growth metrics at the tree and spathe levels. Interannual warming in 2024 advanced dormancy break and spathe onset relative to 2025, with mulch regimes modulating these effects. In 2024, PP+SDPF significantly advanced spathe onset by 4.6 days and reduced Phase A GDD by about 37 %, consistent with enhanced surface moisture retention; SDPF and PWGC+SDPF showed more modest effects. In 2025, cooler conditions attenuated the mulch effects, although the SDPF- and PWGC-based regimes maintained a more stable phenology. At the tree level, PP+SDPF increased the total GDD in 2024 (766 °Cdays) but decreased it in 2025 (581 °Cdays), whereas PWGC+SDPF performed best in 2025. Daily spathe production and growth improved under mulching, whereas the efficiency per GDD remained similar among the treatments. Climate primarily sets the phenological pace, and mulch modulates phase-specific thermal demands and growth dynamics, offering a climate-adaptive, phase-targeted strategy for date palm management in variable arid environments and potentially for other perennials facing increasing climatic variability.