After a long and almost record breaking dry patch of 3-4 months, from mid winter until early spring, 3 Trichocereus cacti have initiated flowering in our garden. It appears that a dry winter period will stimulate flowering in those individuals ready to flower. Especially since this winter was not particularly colder than normal, BUT it was very dry compared to previous years. Living on the coast we still get regular rain over most of the year, with less in winter but still too much perhaps for Trichocereus to initiate flowering. Height may also be another factor as each of the three cacti were between 2-3m tall. So a simple way to initiate flowering might be to just move a potted cactus of 1-2m height into a dry position undercover, outside on a verandah, during winter and to not water at all or to give minimal water. A good watering of a high potassium bloom booster in late autumn might help as well. The cacti that have/will flower are T. bridgesii ‘Psycho0’, T. cuzcoensis and ‘Juuls Giant x (T. pachanoi x SS02)’.
One thing that many Trichocereus growers have observed, for those of us who have lived in different climates or moved cacti when moving house to another state, is that their ability to produce flowers each summer has changed. I noticed this when moving pretty much 200km from the Lockyer Valley to the Sunshine Coast. Where I would only get a few flowers on my Trichocereus, I was now getting none. Same latitude pretty much, only over to the coast. So obviously the major factor I thought must be playing a ole in flowering is a chilling requirement, like you get with stone fruit, apples, pears, etc. Being at the same latitude would eliminate photoperiod for playing a major role, although it could still play a minor one. In the Lockyer Valley we used to get temps just below 0ºC a few nights or a week each year, but in a frost free location. On the Sunshine Coast, the coldest we get a few nights per year is about 3ºC.
Down the southern states of Australia are the main Trichocereus breeders and growers. While up northern states, there are none, breeders anyway, that I know of. So its getting clearer. I was messaging a Brazilian friend the other day about this and we agreed to try and work out a protocol for the Trichocereus flowering in warmer climates.
A paper I came across titled ‘Photoperiod, Irradiance, and Temperature Affect Echinopsis ‘Rose Quartz’ Flowering by Erwin. J. et al. (HORTSCIENCE 51(12):1494–1497. 2016. doi: 10.21273/HORTSCI 10387-16) has shed some light on the requirements of the Echinopsis (the genus of which Trichocereus has been lumped into in recent years) hybrid ‘Rose Quartz’. They found that the cooling requirement for optimal flowering of Rose Quartz was 8 weeks at 5ºC. Erwin also notes that application of Benzyladenine (BA) decreased number of flowers in this hybrid. But noted that the timing of the spraying may be important. In Schumbergia spp. it was noted that when timed with floral differentiation, BA increased flower numbers.
So, my research so far to trigger Trichocereus cuttings to flower in warmer climates like the Sunshine Coast. Not having access to a temperature controlled grow room, I decided that I needed to take the easiest route for it to be worthwhile to growers. I placed 4 different 30cm healed cuttings of Trichocereus clones HB01, HB02, EILEEN and SS02 x JG into my fridge at 5ºC. My initial trial was for 1000hrs or 42 days. after which the cuttings were removed and potted up and placed outside with other cacti. They grew very well and were great looking specimens. However none formed buds or flowered last season.
Aiming to increase cold exposure I settled on 1500hrs at 5ºC, or 9 weeks. This is my current trial and is ongoing. I will also trial Erwins result on Rose Quartz by experimenting with 8 weeks at 5ºC.
Erwin notes that Rose Quartz can be classified as a facultative long day (LD) plant with a facultative cool-temperature requirement for flowering. Determination of whether the cool temperature requirement resulted from vernalisation or overcoming flower bud dormancy would require areole dissection before cooling to determine whether flower buds were present.
Whether it is best to place the cuttings/rooted cacti into 5ºC after the winter solstice to achieve some of the long day requirements, or to just bring them out of cooling in time for the summer flowering season can be determined.
Our results are forthcoming. Hopefully we get good results otherwise this may be out of the reach of homegrowers with no access to a temperature controlled growth chamber 🙂
This is the abstract from Erwins paper:
Photoperiod, irradiance, cool temperature (5 ºC), and benzyladenine (BA) application effects on Echinopsis ‘Rose Quartz’ flowering were examined. Plants were placed in a 5 ºC greenhouse under natural daylight (DL) for 0, 4, 8, or 12 weeks, then moved to a 22/18 ºC (day/night temperature) greenhouse under short days (SD, 8-hour DL) plus 0, 25, 45, or 75 mmol·mL2·sL1 supplemental lighting (0800–1600 HR; 8-hour photoperiod), long days (LD) delivered with DL plus night-interruption lighting (NI) (2200–0200 HR), or DL plus 25, 45, or 75 mmol·mL2·sL1 supplemental lighting (0800– 0200 HR) for 6 weeks. Plants were then grown under DL only. Percent flowering plants increased as irradiance increased from 0–25 to +75 mmol·mL2·sL1 on uncooled plants, from 0% to 100% as 5 ºC exposure increased from 0 to 8 weeks under subsequent SD and from 25% to 100% as 5 ºC exposure increased from 0 to 4 weeks under subsequent LD. As 5 ºC exposure duration increased from 0 to 12 weeks (SD-grown) and from0 to 8 weeks (LD-grown), flower number increased from 0 to 11 and from 5 to 21 flowers per plant across irradiance treatments, respectively. Total production time ranged from 123 to 147 days on plants cooled from 8 to 12 weeks (SD-grown) and from 52 to 94 days on plants cooled for 0–4 weeks to 119–153 days on plants cooled for 8–12 weeks (LDgrown). Flower life varied from 1 to 3 days. BA spray application (10–40 mg·LL1) once or twice after a 12-week 5 ºC exposure reduced flower number. Flower development was not photoperiodic. High flower number (17–21 flowers/plant) and short production time (including cooling time, 120–122 days) occurred when plants were grown at 5 ºC for 8 weeks, then grown under LD + 45–75 mmol·mL2·sL1 for 6 weeks (16 hours; 10.9–12.8 mol·mL2·dL1) at a 22/18 ºC day/night temperature.