Soil medium and watering frequency alter growth and allocation for Blue Diamond cholla (Cylindropuntia multigeniculata), a rare cactus of the northeast Mojave Desert, USA

Blue Diamond cholla (Cylindropuntia multigeniculata (Clokey) Blackb. [Cactaceae]) is a rare cactus of the Mojave Desert. We explored whether cultivation from joint cuttings is a viable method for supporting threatened populations. Terminal joints were collected from adult plants at the type locality and grown in a shade house: We tested whether 2 soil mixes that varied in the ratio of inorganic and organic components (50:50 compared to 85:15) and 2 watering frequencies (250 ml every 5 d compared to 500 ml every 10 d) promote root growth important to outplanting survival. Plants grown from joint cuttings in the 50:50 soil had greater shoot and root biomass, produced more joint segments, and had higher initial and final survivorship over the 5-mo study. Neither soil nor watering treatments shifted biomass allocation to roots as hypothesized, but frequent watering produced longer roots, which may benefit reintroduced plants by assisting root access to deep soil moisture. Despite their vigor during collection, freshly cut joints rapidly declined in condition, resulting in approximately 50% mortality during the first month of the study. Initial mortality was not explained by the identity, condition, or size of the maternal plant. Prior-year weather patterns and collection procedures may influence quality and durability of joint cuttings and require further study. While larger plants were produced from the 50:50 mix, and root length was increased by frequent watering, reintroduction of nursery-grown plants will indicate whether such treatments aid establishment in the dry habitat where this species occurs.