Effects of plant gender, cutting age, and propagation medium on rooting and growth of Juniperus communis cuttings : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Horticultural Sciences, Massey University, Palmerston North, New Zealand

Abstract

Juniperus communis L. is a slow-growing, dioecious conifer of increasing ecological and commercial value, but large-scale production is limited by slow, erratic adventitious rooting. The present study examined the influence of cutting age, plant gender and propagation substrate on survival, and growth of J. communis stem cuttings under greenhouse conditions. Shoots were taken from male and female stock plants and divided into one-year-old and two year-old cutting material. Two-year-old cuttings were propagated in rockwool, pumice, peat: perlite (1:1, v/v), and vermiculite: perlite (1:1, v/v) mix, while one-year-old cuttings were propagated in pumice and vermiculite: perlite (1:1, v/v) mix. Survival, root number, root length, and shoot length were assessed over a nine-month period. Plant gender, propagation substrate and their interaction had significant effects on survival at three, five and nine months after planting in two-year-old cuttings. Overall, well-aerated substrates, particularly pumice and rockwool, consistently promoted better rooting performance than vermiculite:perlite. Male cuttings propagated in pumice and rockwool achieved the highest survival rates (80% and 84%, respectively), whereas female cuttings grown in vermiculite:perlite had consistently low survival (12%). Root number was the most responsive growth parameter, with male cuttings in rockwool and female cuttings in pumice producing the highest root numbers. Cutting age influenced the response to both plant gender and substrate. In two-year-old cuttings, survival and root number were significantly affected by gender, substrate, and their interaction. In contrast, one-year-old cuttings showed more uniform rooting responses, with few significant effects of gender or substrate. Root length in one-year-old cuttings was greater in pumice (82.82 mm) than in vermiculite:perlite (64.96 mm) after five months of propagation. Overall, plant gender and propagation substrate had greater effects on rooting performance in two-year-old than in one-year-old cuttings. Well-aerated substrates, particularly pumice and rockwool, promoted more favourable rooting than vermiculite:perlite, while one-year-old cuttings exhibited more consistent propagation outcomes. These findings demonstrate that cutting age, plant gender, and substrate selection should be considered jointly when developing vegetative propagation protocols for J. communis. Developing reliable vegetative propagation methods will support its ecological restoration, conservation, and commercial cultivation.