At a glance
RECORDED PROFILE DATA- Minimum night temperature for most Angraecum
- 55 °F (13 °C)
- Typical day temperature during active growth
- 20‑27 °C (68‑81 °F)
- Rest‑period night temperature for cool‑mountain species
- 5‑10 °C (41‑50 °F)
Why Seasonal Temperature Matters for Angraecum
Orchid metabolism is temperature‑driven. During the day photosynthesis creates carbohydrate reserves, while at night respiration uses those reserves. A drop in night temperature slows respiration, allowing the plant to store energy for the next growth cycle and to trigger flowering hormones. The American Orchid Society explains that many orchids need a significant day‑night temperature difference to induce blooms, and the same principle applies to most Angraecum species[12].
General Temperature Classes for Angraecum
The genus spans lowland, warm‑growing species and high‑altitude, cool‑growing taxa. The American Orchid Society’s greenhouse guide divides orchids into three temperature classes: warm (night ≥15 °C), intermediate (night ≥13 °C) and cool (night can fall to 5 °C) [1]. Angraecum species fall mainly into the intermediate class, with a few cool‑mountain exceptions.
Optimal Day‑Night Ranges for Active Growth (Spring–Summer)
| Growth Phase | Day Temperature | Night Temperature | Typical Species |
|---|---|---|---|
| Active growth | 20‑27 °C (68‑81 °F) | 15‑20 °C (59‑68 °F) | Most Angraecum, e.g., A. sesquipedale[8] |
| Warm‑lowland species | 22‑28 °C (72‑82 °F) | 18‑22 °C (64‑72 °F) | A. leonis (cultivation notes give 84‑85 °F day, 69‑71 °F night during rest, indicating a higher growth set‑point)[5] |
| Cool‑mountain species | 18‑22 °C (64‑72 °F) | 12‑16 °C (54‑61 °F) | A. cultriforme (summer day 25‑26 °C, night 19‑20 °C)[6] |
These ranges are consistent with the minimum night temperature of 55 °F (13 °C) reported for Angraecum in a 1980s orchid‑doctor compilation[10]. Maintaining humidity of at least 60 % (the same source recommends) helps avoid stress when temperatures are on the cooler side.
Recommended Rest (Winter) Conditions
Most Angraecum benefit from a cooler, drier period of 6‑8 weeks after flowering. The goal is to lower night temperatures by 5‑8 °C while keeping days only slightly cooler. Example rest regimes:
- Intermediate species (e.g., A. sesquipedale): Day 18‑22 °C (64‑72 °F), night 12‑16 °C (54‑61 °F). No major reduction in watering; humidity can be lowered to 50‑60 %.
- Warm‑lowland species (e.g., A. leonis): The culture sheet for A. leonis records winter days around 29 °C (84‑85 °F) and nights 21‑22 °C (69‑71 °F) with a diurnal range of ~8 °C[5]. For these, a modest night drop to 18‑20 °C (64‑68 °F) is enough to signal rest without stressing the plant.
- Cool‑mountain species (e.g., A. sororium): RHS hardiness ratings list H2 (1‑5 °C) and H3 (‑5 to 1 °C) as possible outdoor limits[4]. In a greenhouse, aim for night 5‑10 °C (41‑50 °F) and day 12‑15 °C (54‑59 °F) for a strong rest period.
Practical Steps to Implement Seasonal Temperature Shifts
- Know your species’ native elevation. Montane species (often from >1500 m) need cooler nights; lowland taxa can stay warmer.
- Set thermostat schedules. Reduce night set‑point by 5‑8 °C about 2‑3 weeks before the expected rest period.
- Increase airflow at night. Cool, moving air prevents cold‑draft damage while allowing the temperature drop.
- Adjust watering. Decrease frequency during rest; a light mist once a week is sufficient for most intermediate species.
- Monitor humidity. Keep it above 60 % for active growth; allow it to fall to 50‑60 % during rest to reduce fungal risk.
- Track plant response. Look for new leaf emergence (growth) after the rest period and for healthy leaf coloration. If leaves yellow or become limp, the night temperature may be too low.
Troubleshooting Common Temperature‑Related Issues
| Symptom | Likely Cause | Action |
|---|---|---|
| Stunted new growth or no leaf expansion | Night temperatures remaining too high (above 20 °C) during growth phase | Increase night‑time cooling by 3‑5 °C; improve night ventilation. |
| Leaf edges brown and crisp | Night temperatures below the species’ minimum (e.g., <5 °C for intermediate taxa) | Raise night set‑point; add a low‑intensity heater or close vent curtains. |
| Failure to flower after rest | Insufficient night‑day temperature differential (less than 5 °C) | Ensure day temps are 5‑8 °C higher than night during the 6‑8 week rest. |
Putting It All Together: A Sample Calendar
Assuming a temperate greenhouse that can be programmed:
- Jan‑Mar (Rest): Day 18‑22 °C, Night 12‑16 °C; water weekly, humidity 50‑60 %.
- Apr‑Jun (Growth Ramp‑up): Increase night to 15‑18 °C, day to 22‑25 °C; resume regular watering.
- Jul‑Sep (Peak Growth): Day 24‑27 °C, Night 18‑20 °C; feed weekly with quarter‑strength fertilizer.
- Oct‑Dec (Pre‑Rest): Gradually lower night by 2 °C each week to reach target rest temperatures by early November.
Adjust the schedule for species that naturally inhabit higher elevations (e.g., A. sororium) by extending the cooler phase and lowering night set‑points further.
Key Take‑aways
- Maintain day 20‑27 °C and night 15‑20 °C for most Angraecum during growth.
- Provide a 5‑8 °C night‑day drop for 6‑8 weeks in winter to induce a healthy rest.
- Cool‑mountain species may tolerate night temps as low as 5‑10 °C; they benefit from a stronger cooling period.
- Use thermostats, night ventilation, and humidity control to achieve and monitor these ranges.
FAQ
How much should the night temperature drop to trigger flowering?
Most Angraecum respond to a night‑day difference of 5‑8 °C (9‑15 °F). The American Orchid Society notes that a significant drop is essential for many orchids to store energy for bloom production[12].
Can I keep my Angraecum at a constant 22 °C year‑round?
A constant temperature eliminates the seasonal cue that many Angraecum need for rest and flower induction. Without a cooler period the plant may grow vegetatively but fail to bloom, and long‑term vigor can decline.
My high‑elevation Angraecum is yellowing; could the temperature be too high?
Yes. Cool‑mountain species such as Angraecum sororium are tolerant of night temperatures down to 5 °C. If night temperatures stay above 15 °C they can experience stress, manifested as yellowing or leaf softening.
FOLLOW THE EVIDENCE
Sources & references
- American Orchid Society, Caring for Orchids in the Greenhouse, https://www.aos.org/orchids/articles/caring-for-orchids-in-thegreenhouse
- Royal Horticultural Society, Angraecum sororium, https://www.rhs.org.uk/plants/1293/angraecum-sororium/details
- OrchidCulture.com, Angraecum leonis Culture, https://www.orchidculture.com/COD/FREE/FS257.html
- OrchidCulture.com, Angraecum cultriforme Culture, http://www.orchidculture.com/COD/FREE/FS828.html
- OSCOV, Angraecum sesquipedale by Hans Proebsting, https://oscov.asn.au/articles/angraecum-sesquipedale-by-hans-proebsting/
- Orchids.org, ANGRAECUMS: Minimum Optimums, https://www.orchids.org/articles/angraecums-minimum-optimums
- American Orchid Society, Why Orchids Need a Drop in Nighttime Temperature, https://www.aos.org/orchids/articles/why-orchids-need-a-drop-in-nighttime-temperature