Optimum Moisture Conditions for English Lavender Cuttings Are Drier for Root Development than Shoot Development

Abstract

Providing proper moisture conditions is critical for successful cutting propagation. This study aimed to investigate the optimal substrate moisture level for enhancing the survival and rooting rates of Lavandula angustifolia cuttings. Apical cuttings of L. angustifolia were propagated under four irrigation thresholds (−1.0, −2.5, −5.0, and −10.0 kPa) over six weeks. At the final harvest, cuttings grown at −2.5 kPa demonstrated the highest survival rate (83.3%), and those grown at −10.0 kPa demonstrated a mortality > 50%. A high rooting percentage (53.0 and 47.2%) was observed in cuttings grown at −1.0 and −2.5 kPa, while the lowest rooting percentage (<10%) was present in those grown at −10.0 kPa. Adventitious root formation and root growth occurred within a month for all treatments, except for the −10.0 kPa treatment; the general root growth was similar among treatments at the final harvest. Shoot growth was negligible in all treatments until four weeks, and it increased rapidly with increasing substrate moisture levels after the formation of adventitious roots. The adventitious root system was established within four weeks, which was followed by accelerated leaf and shoot growth. The optimal substrate moisture level for high survival and rooting of English lavender cuttings was approximately −2.5 kPa, but higher moisture tension at −1.0 kPa could enhance the shoot growth after adventitious roots are established.