Introduction to Orchid Species Culture Climate Tables. By Charles and Margaret Baker’s.

Orchid Species Culture Sheets are designed for orchid growers all over the world. Information is formatted for growers from north or south of the equator, and both English and metric units of measure are used.
A climate table is included with each Orchid Species Culture sheet. The following is a brief description of the information contained in each line of the table. We believe that if the user understands the way the information is formatted in the climate table, it will be easier to use.
Growers north of the equator should start with the months listed across the top of the table, on the N/HEMISPHERE line, and read down a column to find the average conditions for any given month. If the northern hemisphere grower wants the information in English units of measure, they simply use the top of the table, but if metic units of measure are more comfortable, then all they need to do is use the lines near at bottom of the table.
On the other hand, growers south of the equator should start with the months across bottom of the table, on the line headed S/HEMISPHERE, and read up the column.

Culture Climate Tables Example.

F AVG MAX 72 73 73 75 76 79 81 82 81 78 76 74
F AVG MIN 60 60 62 64 65 67 68 68 68 66 63 61
DIURNAL RANGE 12 13 11 11 11 12 13 14 13 12 13 13
RAIN/INCHES 2.2 2.1 2.7 4.2 5.7 6.3 3.7 3.0 5.2 3.9 2.3 3.4
HUMIDITY/% 83 84 86 84 86 85 82 83 84 85 82 84
BLOOM SEASON * * * ** *** ** * * * * *
DAYS CLR @ 9AM) 10 12 6 3 2 2 6 6 7 8 12 13
RAIN/MM 56 53 69 107 145 160 94 76 132 99 58 86
C AVG MAX 22.2 22.8 22.8 23.9 24.4 26.3 27.3 27.8 27.2 25.6 24.4 23.3
C AVG MIN 15.6 15.6 16.7 17.8 18.4 19.5 20.1 20.1 20.1 18.9 17.3 16.2
DIURNAL RANGE 6.6 7.2 6.1 6.1 6.0 6.8 7.2 7.7 7.1 6.7 7.1 7.1

Weather stations are usually located at airports, and airports seldom grow where orchids do, so the temperatures recorded at the station are sometimes calculated for the habitat elevation using standard atmospheric lapse rate formulas. This is done anytime there is a large difference in elevation between the station and the habitat. Also, growers need to remember that climate data does not reflect any of the microclimate conditions that might exist in the habitat. Therefore, growers should not attempt to duplicate the conditions exactly. First, it isn’t possible, and second, the information is all averaged. The data should instead be used to determine approximate temperatures and the general timing and magnitude of seasonal changes for each species.

Table notation.

    • N/HEMISPHERE  JAN  FEB  MAR  APR  MAY  JUN  JUL  AUG  SEP   OCT  NOV  DEC – Northern hemisphere months for which the averages are reported.
    • °F AVG MAX Average – daily maximum (warm) temperature for each month of the year in degrees Fahrenheit. Actual daily highs usually range several degrees above and below this average.
    • °F AVG MIN Average – daily minimum (low) temperature for each month of the year in degrees Fahrenheit. Actual daily lows normally range several degrees above and below this average.
    • DIURNAL RANGE – This is the daily range between the average high and low temperatures in degrees Fahrenheit. The seasonal increases or decreases often serve as the bloom initiator for many orchid species, and the seasonal pattern should be approximated for cultivated plants.
      It should be noted that if a given habitat is located some distance inland and the only climate data available is from a nearby coastal station, conditions in the habitat may be somewhat different than indicated in the climate table. Because of the moderating influence of the ocean, actual daily high temperatures in the habitat may be several degrees warmer, minimum values may be somewhat cooler, and the diurnal range is, therefore, greater than indicated in the table. In any event, growers should not try to duplicate the values exactly. Rather, these averages are intended to provide probable acceptable values for each species as well as indicate the pattern of seasonal changes.
    • RAIN/INCHES – The average monthly rainfall shown in inches. This is accurate only at the location where it was recorded and may vary greatly over even short distances, especially in hilly or mountainous terrain. It does, however, indicate the seasonal rainfall pattern for a region and gives growers a good idea of the length and magnitude of wet and dry seasons. These patterns should be followed fairly closely for cultivated plants, because they are another of the conditions that may initiate blooms.
    • HUMIDITY/% – The average monthly relative humidity. This is accurate only at the weather station where it was recorded, but it does indicate the kinds of seasonal changes that occur in the region, and it is a helpful tool in determining how dry a dry season might be.
      Growers should understand that unless the moisture content of the air is changed, humidity always declines as temperature increases. Conversely, humidity rises as temperatures fall.
      The difference between day and night temperatures strongly affects average humidity. During the wet season in a habitat, when there is little difference between day and night temperatures, the actual daily high and low humidity may vary as little as 10% above and below the average. An opposite extreme may occur during the dry season when there is a large diurnal temperature range. Under these circumstance, humidity averages may differ 30-40% above and below the recorded average.
      A separate, more comprehensive discussion of humidity and how it works is available in Increasing Relative Humidity article. It provides additional information about how to control humidity in a growing area.
    • BLOOM SEASON – Most of the bloom times were compiled by Robert Hamilton in his book, “When Does it Bloom”.
    • DAYS CLR @ 7AM, 2PM, etc. – This abbreviation stands for Days Clear at 7AM. It is the average number of clear days each month at the weather station at the indicated time. This is the average number of days each month when less than 0.3 of the sky is covered by clouds. Some days may have a very thin cloud layer, and it may seem bright, but the skies are not considered clear. Again, these values are completely accurate only at the weather station where the observations are recorded, but they do serve as a guide to indicate regional changes in seasonal light. Growers may use this information to determine when to apply shading, when to increase light, or whether a plant might do better with high morning or afternoon light.
    • RAIN/MM – The average rainfall each month, shown in millimeters.
    • °C AVG MAX – The average daily maximum (warm) temperature for each month of the year as discussed above, shown in degrees Celsius.
    • °C AVG MIN – The average daily minimum (low) temperature for each month of the year as discussed above, shown in degrees Celsius.
    • DIURNAL RANGE – The same as indicated above, except in this location in the table, it is shown in degrees Celsius.
    • S/HEMISPHERE  JUL  AUG  SEP  OCT  NOV  DEC  JAN  FEB  MAR  APR   MAY  JUN – Growers in the southern hemisphere should use this guide. The months are shown relative to the season for which the averages are reported.

We hope that all of this will help readers use the Orchid Species Culture Sheets more easily and effectively. Remember, do not try to duplicate the indicated conditions exactly, but most plants are healthiest if the seasonal temperature changes and rainfall cycles are approximated.
Hopefully, this will result in happier plants which, in turn, makes for happier, more satisfied growers.
Charlie and Marg. Baker —