Saturday, January 26, 2013

Stanhopea Temperature Requirements



Stanhopea grow well in Tropical and Subtropical climates and many orchid enthusiasts would place them in temperature classifications of intermediate to warm growing.  There are some exceptions and several species tolerate intermediate to cool conditions as well.  Those species that are tolerant of cooler conditions are better suited for growing outside here in southern California due to our cool nights during the winter.  However, most Stanhopea benefit from growing outdoors during the summer and many species are more floriferous when grown outdoors.

There are several temperature classifications for orchids that could apply to the three classes I have described above, however for the uses of growing Stanhopea, I have modified some of these classifications.  The warm classification is primarily 60.0-65.0°F (15.5-18.3°C) average temperatures during winter nights, the intermediate classification is 50.0-60.0°F (10.0-15.5°C) average temperatures during winter nights, and the cool classification is 40.0-50.0°F (4.4-10.0°C) average  temperatures during winter nights.  These classifications are only a general guide for these orchids and some species grow quite comfortably in more than one classification.  Some species such as S. oculata can be found growing well in all three classifications.  This temperature tolerance may be due to the broad distribution of this species and the ability of it to adapt to a wide range of temperature regimes.  Stanhopea oculata successfully grows outdoors in the U.S.in such differing climates as Hawaii, Florida, southern California, and Puerto Rico.  For a complete list of recognized species and temperature requirements see the Stanhopea Temperature Requirements Table 

Here in San Diego my Stanhopeas have been subjected to temperatures as low as 31.0°F (-0.6°C) and as high as 105.0°F (40.6°C).  I expected some damage to the leaves of the Stanhopea plants with the lowest temperature just below freezing, but no long term damage was evident.  Even a few weeks after the light freeze, there did not appear to be any damage to the plants.  One factor that could have assisted the orchids is that I grow many of them under the canopy of trees, and these canopies may have protected them from frost.  The warmest temperatures of 105.0°F (40.6°C) are often accompanied by low humidity and drying winds, so I usually mist or even water the plants daily for the few days in the year when there is excess heat.  Just to clarify, the extreme temperatures listed above were only for brief periods of time, and Stanhopea cannot tolerate extremes in heat or cold for extended periods of time.

The average temperatures in my growing area for winter are 46.0°F (7.8°C) at night and 65.0°F (18.3°C) during the day.  The average summer temperatures in my growing area are a bit higher than San Diego's listed temperatures due to the fact that I live a few miles inland from the ocean.   The average summer temperatures are 65.0°F (18.3°C) at night and 84.5°F (29.2°C) during the day in my  growing area.  These relatively mild conditions are appropriate for growing several of the intermediate to cool tolerant species such as S. oculata, S. tigrina, and S. wardii.  These three species are what I call the “Big Three” of Stanhopea culture because they are easy to grow and relatively easy to obtain from orchid nurseries in my region.  The warm growing species such as the hornless Stanhopeas, S. annulata, S. cirrhata, and S. pulla and the Candida group (S. candida, S. grandiflora, and S. reichenbachiana) require warm temperatures during the winter [nothing below 60.0°F (15.6°C), if only briefly].  These warmer growing species also seem less tolerant of low humidity conditions and tend to exhibit leaf browning as humidity is reduced.
Stanhopea tigrina var. nigroviolacea 'Predator' on left, Stanhopea tigrina var. nigroviolacea center and left

When choosing a Stanhopea to grow, try to ensure that you can provide the best growing conditions that match the natural growing conditions of the species.  For example S. tigrina grows in the mountains west and north of Veracruz at elevations from 1,969 to 5,577 feet (600-1,700 m).  We can learn a great deal about the temperature requirements of a plant by reviewing the climate of the area that it is native to.  This is not a new concept and other growers have eloquently described this in detail.  I have chosen the city of Jalapa, Mexico to demonstrate this concept.  Jalapa is located at an elevation of 4,682 ft (1,427 m) near the upper range of S. tigrina distribution.  Stanhopeas are not native to the city proper but are native to the region surrounding the city, so this provides us with a general idea of what temperatures S. tigrina is subject to (see Table 1 below).  This table provides us with some key pieces of information for growing S. tigrina. First, winter low temperatures range between 52.2-57.6°F (11.2-14.2°C). Second, the two following months in April and May are the warmest months for average high temperatures for the year, and that there is a 19.8-22.3°F (10.5-12.4°C) difference between night and day temperatures known as the diurnal temperature change during the winter months prior to this.  This shift in temperatures appears to have an impact on some Stanhopea species’ ability to increase flower production.  Several growers have had difficulty in blooming Stanhopea species in a more controlled environment (e.g., a greenhouse), but after moving the plants outdoors in spring and summer the plants bloomed more regularly and with more inflorescences. For more information on S. tigrina habitats see Edouard Faria’s blog Stanhopea Passion - Stanhopea tigrina.


Tabel 1. Temperature data for Jalapa, Mexico                  
Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year Avg.
Average high °F 71.4 73.0 79.9 80.4 82.9 78.4 77.4 78.3 78.3 77.0 74.7 72.7 77.0
Average high° C 21.9 22.8 26.6 26.9 28.3 25.8 25.2 25.7 25.7 25.0 23.7 22.6 25.0
Average low °F 52.5 52.2 57.6 59.9 63.1 61.0 60.6 61.2 61.5 59.4 57.2 54.0 58.3
Average low °C 11.4 11.2 14.2 15.5 17.3 16.1 15.9 16.2 16.4 15.2 14.0 12.2 14.6
Data collected from WorldClimates.com

I grow all of my intermediate to cool growing Stanhopea outdoors throughout the year.  The success I have growing and blooming these species is in large part due to the temperature range of the region I live in, and similarities to the temperatures that species such as S. tigrina experience in nature (see Tables 1 & 2). For example, in my area of San Diego our average winter low temperatures are a little lower than Jalapa at 48.9-52.8°F (9.4-11.6°C), but within the range of temperature variation within the distribution of S. tigrina.  These average winter low temperatures appear to be comfortable for this species and they often continue to grow through January in my area.  This species also performs very well growing outdoors in Santa Barbara, California where the average winter low temperatures are colder 40.3-45.2°F (4.6-7.3°C) (see Table 3).  The winter temperatures in Santa Barbara are cooler than the temperatures in Jalapa, but this adjustment to lower temperatures probably represents temperature tolerance and variability in the species. 


Table 2. Temperature data for San Diego, California                
Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year Avg.
Average high °F 65.9 66.5 66.3 68.4 69.1 71.6 76.2 77.8 77.1 74.6 69.9 66.1 70.8
Average high °C 18.8 19.2 19.1 20.2 20.6 21.9 24.5 25.4 25.1 23.6 21.1 18.9 21.6
Average low °F 48.9 50.7 52.8 55.6 59.1 61.9 65.7 67.3 65.6 60.9 53.9 48.8 57.6
Average low °C 9.4 10.4 11.6 13.1 15.1 16.6 18.7 19.6 18.7 16.1 12.2 9.3 14.2
Data collected from climate-zone.com



Table 3. Temperature data for Santa Barbara, California                
Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year Avg.
Average high °F 63.7 64.6 65.3 67.4 68.6 71.2 73.9 75.4 75.2 73.1 68.5 64.4 69.3
Average high °C 17.6 18.1 18.5 19.7 20.3 21.7 23.3 24.1 24.0 22.8 20.3 18.0 20.7
Average low °F 40.3 43.2 45.2 47.1 50.1 53.6 56.9 58.2 56.5 51.5 44.7 40.1 49.0
Average low °C 4.6 6.2 7.3 8.4 10.1 12.0 13.8 14.6 13.6 10.8 7.1 4.5 9.4
Data collected from climate-zone.com

The month of April is the first month of inflorescence initiation of S. tigrina in my collection and this coincides with a 13.5-17.0°F (7.5-9.4°C) diurnal temperature change in the winter months prior to initiation.  While these diurnal temperature changes are not as dramatic as those in Jalapa, these appear to be enough to encourage the S. trigrina to be consistent in flower production each year and more floriferous.  This is not to suggest that Stanhopeas cannot be grown in greenhouses and bloom successfully.  Several growers have successfully grown and flowered Stanhopeas in warm conditions.  However, it has been my experience that many Stanhopea including S. tigrina grow better, and are more floriferous growing outside here in southern California  rather than in a greenhouse.  I know of several growers who had difficulties blooming S. tigrina until they moved the plants outdoors.  Barney Greer in his book The Astonishing Stanhopeas provides several examples of species (e.g., S. florida, S. maculosa,  and S. platyceras) that he could not bloom in his greenhouse, but when moved outdoors they began to flower.  Other species of Stanhopea that he grew outdoors as a matter of preference (e.g., S. deltoidea, S. martiana, S. ospinae, S. pozoi, S. tigrina, and S. wardii) and others that grow best in a greenhouse with cool [50.0°F (10.0°C)] night conditions (e.g., S. embreei, S. guttulata, S. hernandezii, S. insignis, S. panamensis, S. posadae, S. ruckeri, S. stevensonii).

If you are having difficulties in blooming some of these Stanhopea you may want to try growing them outdoors if you have the proper climate, or move them outdoors for the summer.  Outdoor diurnal temperature changes between [15.0-20.0°F (8.3-11.1°C)] should provide the proper conditions to initiate flowering.  If you don’t have the option of growing Stanhopeas outdoors, try lowering the temperature of the greenhouse during the night in winter and summer a few degrees, down to 55.0°F (12.7°C) or even 50.0°F (10.0°C), if your other plants can tolerate that treatment, you should have an increased chance in flowering your Stanhopea.  Linda Kraus in her article in the American Orchid Society Bulletin “The Culture of Stanhopeas – Confession of a Requited Love” stresses that she grew her Stanhopeas cool with night temperatures of 52.0°F (11.1°C) even in the summer.  Thus she kept her Stanhopeas in a cool greenhouse condition and they bloomed well.

Printed References:
Greer, B. 1998.  The Astonishing Stanhopeas The Upside-down Orchids. Self Published.

Kraus, L. 1984. The culture of Stanhopeas – “Confessions of a Requited Lover”. AOS Bulletin 53(4): 358-366.


1 comment:

  1. Very interesting information, i grow some plants at Greece (indoors) because winter nights here fall below zero, some times to -17 to -20 for a week or two.

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