The effects of relative humidity and substrate moisture on rooting of hybrid hazelnuts from hardwood stem cuttings

Hybrid hazelnuts (Corylus americana Walter x C. avellana L.) are currently being bred for use as a cold-hardy perennial crop that could produce profits for Midwestern farms while supporting agroecosystem sustainability. However, asexual propagation techniques for producing germplasm for breeding and dissemination purposes have proven difficult. This study was one of a series attempting to develop a protocol for hardwood stem cutting propagation. This study assessed the impact that relative humidity (RH) and substrate moisture has on rooting of hardwood stem cuttings propagated in low-cost humidity tents. Hardwood stem cuttings retrieved from 14 hybrid hazelnut genotypes were planted into enclosed humidity tents, each housing 64 cuttings. Treatments were RH thresholds of 30%, 50%, 70%, and 90%, which were maintained by daily monitoring and watering to saturate the substrate when a tent’s RH fell below its specified RH threshold. Cuttings propagated in 50% and 70% RH tents showed the highest rates of rooting at 16% and 12% respectively, whereas only 7% of cuttings rooted at 90% RH and 3% at 30% RH. By showing that intermediate RH levels and watering regimes are optimal for rooting, these results suggest daily monitoring is not necessary for hardwood stem cutting propagation of hybrid hazelnuts.