Temperature Affects Cacti and Succulent Development Rate

Seventeen succulent and one cactus species (1-2 year old) grown in 5.7cm diameter plastic pots in a soilless media were received from Altman Plants, Inc. (Vista, CA) on November 5.  Plants were unpacked and acclimated in greenhouses for 2 weeks (22/18C day/night temperature; under natural photoperiod) in St. Paul, MN.  The uppermost unfolded leaf (succulents) or tubercle (cactus) was marked, and plants were then placed in growth chambers, where leaf/tubericle temperature was maintained at constant 10, 16, 22 or 28C.  Irradiance was maintained at 300 μmol m^-2 s^-1, the photoperiod was 12 hr, plants were watered as needed, and plants were fertilized twice a week with 400 ppm N from 15-0-15 fertilizer (Dark Weather Feed).   After 10 weeks, nine species (more rapid leaf/tubericle unfolding) were removed from chambers and the number of unfolded leaves/tubercles above the previous mark was counted.  A second group of nine species with a slower leaf/tubericle unfolding rate was removed after 15 weeks.  Development rate for each species and at each temperature was calculated.  The experiment was replicated four times over time.  Leaf/tubericle unfolding rates increased as temperature increased from 10 to 22C for 16 species.  The leaf unfolding rate of eight of these species continued to increase as temperature increased from 22 to 28C.  In contrast, with six species, leaf/tubericle unfolding rate decreased as temperature increased from 22 to 28C.  Sempervivum calcareum and Sedum hybrid ‘Burrito’ (‘Burros Tail’) died when temperatures increased from 22 to 28C.  In contrast, Andromischus critatus ‘Key Lime Pie’ and Crassula arborescens ‘Silver Dollar Jade’ leaf-unfolding rate increased as plant temperature increased from 10 to 16 and then decreasing as temperature was further increased to 28C; C. arborescens died when growth at constant 28C.