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.

Stanhopea Winter Culture Checklist

• Water these species (S. hernandezii, S. jenischiana, S. leitzei, S. maculosa) sparingly during the winter and stop fertilizing them.These Stanhopeas will need less water and a little more sun in order to provide them with a rest period that will enable them to produce more flowers the following spring/summer.

• Fertilize other species that are still actively growing. I prefer to use the low nitrogen “fish emulsion” at this time of the year.  Make sure to purchase the deodorized form, for a more pleasant growing atmosphere. I only fertiilize with half of the recommended strength of all fertilizers I use on Stanhopeas.

• Weed baskets to prevent ferns and other plants from taking up space in the baskets.  While these plants often improve the aesthetic appearance of an orchid basket, they can often steal vital nutrients from the orchid.

• If you grow your Stanhopeas outdoors, ensure that the trees providing them shade have been pruned to let the plants receive more light at this darker time of year.

• Store away saran shade cloth until spring if no direct sun reaches the plants.

• Use of metaldehyde products is advised on a weekly basis to prevent slugs from disfiguring new growth and impacting inflorescence and bud growth on Stanhopeas.  There are also several other methods discussed on the American Orchid Society website at this link AOS Orchid Snail and Slug Treatment.  This link also includes environmental friendly slug control products.  These alternative methods are something to consider if pets or other wildlife can gain access to the growing area.

• Check often for damage done by wind, storms, or pests such as spider mites.

• If extreme cold is forecast [temperatures below 32F (0C)] make sure to provide overhead protection for your Stanhopeas or move them to a warmer location.  Frost can also have detrimental impacts on the foliage of some species, especially maturing new growth.

Why Won't My Stanhopea Bloom?

 

This is one of the most common questions I receive from orchid growers.  Another related question is why do Stanhopeas not bloom consistently each year? The answers are not necessarily straight forward and all encompassing.  Some of the reasons why Stanhopeas do not bloom are because they are too immature to bloom, are planted in the incorrect media or containers, the general growing conditions are not understood well, and that they are not given proper care.

Stanhopeas only bloom on mature pseudobulbs, so if you purchase a seedling instead of a division of a plant, then it may be a few years before your plant blooms.  Small seedlings of only two years of age may take five or more years to mature.  Recently divided plants may not bloom for a year or two, and take time to recover depending on the size of the division and the time of year that the division was taken.  Repotting or re-basketing may also delay bloom of Stanhopeas for a year or more.  Several growers have reported that they have no setback in bloom times from dividing or repotting Stanhopeas.  However, I have been following this more carefully over the past few years and have recorded approximately 50 percent of my Stanhopeas negatively impacted due to division or repotting.  Most of the ill effects are lower flower counts on the inflorescences, or early termination of new inflorescence growth.

Stanhopea panamensis - second flowering of the
year in December after main flowering in October.

 

It is advised to grow Stanhopeas in baskets because they produce pendent inflorescences that grow through the potting media .  I have received several Stanhopeas from people who did not want the plants any longer because they could not get them to bloom. When I received the orchids I found they had been grown in pots, not baskets.  When I repot the plants into a basket, I often find several old inflorescences that could not grow out of the pot from the last flower season.  After re-basketing, the plants began to flower normally each year.

Knowing the proper care provided to the species of Stanhopea you are growing often leads to an increase in flower production.  Some species such as S. annulata, S. avicula, S. candida, S. cirrhata, S. ecornuta, and S. grandiflora (including several others) require more tropical night temperatures throughout the year and bloom best when winter night temperatures do not drop below 65F (18C).  Other Stanhopeas inhabit areas where they receive less water and more sunlight during the winter months.  These Stanhopeas that require a rest period include S. hernandezii, S. insignis, S. jenischiana, S. leitzei, S. maculosa, and S. martiana.  I usually place these Stanhopeas under a roof overhang or under a plastic roof during the winter so that no rainfall can penetrate the growing medium.  I then keep these sparingly moist, but never let them completely dry.  I start regular water of these species in mid spring, when growth starts.  For these Stanhopea, the dryer conditions and increased light during the winter tend to force them to enter into a rest period that they require in order to flower well in the following spring/summer.

Stanhopea panamensis - close up. 
Once your Stanhopeas increase in size they
often will bloom more than once a year.

One common problem Stanhopea growers share is that they are unsuccessful in consistently blooming their Stanhopeas in greenhouses.  In fact, Barney Greer mentions several species (S. florida, S. maculosa, and S. platyceras,) that he had growing in a greenhouse in Sydney, Australia that refused to bloom until he divided the plants and placed them to grow outside.  During the next flowering season the plants began to flower regularly.  The reason why this may occur is that some species of Stanhopea bloom more profusely with a 20-30F (approximately 10-15C) degree shift between day and night temperatures.  These shifts in temperature are best achieved by growing the orchids outdoors in the spring and summer.  Since several species of Stanhopea can grow and bloom well outdoors in southern California, I choose to grow my collection outdoors year around, and then shelter those that need either more warmth, or less water in the winter months.  If you cannot grow your Stanhopeas outside the entire year, try growing them outside in the spring and summer months.  Most growers that have tried the technique of growing Stanhopeas outside when the temperatures are warm enough have had an increase in success flowering their plants.

Additional care that can cause inconsistent flowering includes too little water during the growing season, or being placed in too much sun, and not enough humidity.  When I first began growing Stanhopeas, I placed them in a specific location that received dappled sun throughout the day.  The tree that provided the shade had lost some foliage and branches and one of the Stanhopeas was severely burned.  The plant could no longer grow in that location, with too much sun and not enough water and humidity throughout the day.  I repotted the Stanhopea and placed it in more shade.  The plant slowly recovered and new growth began, but after that improper care, the plant did not bloom for five years.  Just remember that if your plant has some type of a setback or improper care for some time, it may not bloom for a year or more.

Some individuals find that fertilizing Stanhopeas more can increase flower production.  I only fertilize to ensure that the plants are growing large enough and the pseudobulbs are mature enough to flower.  Other than this, I have found that no other fertilizing is necessary to spur plants to bloom.

Too much shade is usually not a problem, but could be the cause for some Stanhopeas to not bloom.  I usually keep my Stanhopeas on the north side of my house and they either receive dappled sun the year around or indirect sun with the only shade coming from the building.  I often provide a little extra shade by stretching saran cloth over the growing area during the summer months and when temperatures are very high (above 90F or 32C).

If you follow these general guidelines, you should be able to increase your chances that your Stanhopeas will bloom, and do this consistently each year.  Being patent is a requirement though, and it may take several years for your Stanhopeas to produce good sized growth in order to flower.  For reference and indications that your Stanhopeas are growing appropriately, see the post 'How do you know your Stanhopea is happy?'