wetting the floors and the benches between the pots with an occasional light 
spraying of the plants. Caution: Do not spray plants in dark, cloudy weather or 
late in the day. A relative humidity of between 60° and 80° is desirable. During 
cold, dark days little if any dampening or watering should be done. 
The above suggestions apply mostly to flowering size plants. Where seed- 
lings below flowering sizes are being raised, the general rule is to keep them 
warmer, more shaded, and more moist. With seedlings, we seek vegetative growth 
and are not concerned about hardening off and practices necessary for good flower 
production. In ventilating mature plants, we must attempt to keep the air in our 
house cool and moist at all times, if possible. On a normal day, as the temperature 
rises to the middle or high seventies F., it is advisable to provide some ventilation 
to cushion the rise. Try to avoid cold drafts or rapid changes in temperature. An 
illustration of poor ventilating would be if the orchid fancier let the temperature 
in the greenhouse rise to 90° F. or above and then opened the ventilators wide 
to let in a rush of cold air with a subsequent drop of 15° to 20°. A gentle rise and 
fall in temperature is desired. Remember that one inch of ventilation on a windy 
day is equivalent to ten inches or more on a calm day. Throughout southern Cali- 
fornia, where the conditions are semi-arid, the common “desert cooler” has proven 
to be of great benefit in growing orchids. This conditions the air on the evapo- 
rative principle. The cooler consists of a metal box in varying sizes, the sides of 
which are louvered frames filled with wood wool. Water is trickled through this 
wood wool by a circulating pump. The air is drawn through these sides and blown 
into the greenhouse by a fan inside the cooler. The principle is that the hot dry 
air when drawn through the wet pads is moistened and lowered considerably 
in temperature. On hot, dry summer days when the outside temperatures are 
running into the 90's, it is possible to keep the temperature 10° or 15° lower. 
This type of ventilator or air conditioner is suggested for those persons living in 
localities where the climate is hot and dry during certain times of the year. 
Because the Cattleya is a tropical plant, it is common belief that high tem- 
peratures are essential. The Cattleya is an intermediate house subject. Though 
the temperatures recommended here may vary somewhat, experience has shown 
that these are safe averages. A minimum night temperature of about 60° the year 
around is advised. On cold nights if the temperature dips into the high 50's, no 
harm will come. Some growers try to maintain minimum night temperatures of 
from 62° to 65°. Higher night temperatures of from 65° to 70° are definitely 
advised for seedlings up to flowering size, but in small greenhouses where all 
genera and age groups are grown in one house, an average of from 60° to 65° 
is best. The temperature can rise in the day time according to the weather and 
season of the year. A good general rule is to adjust conditions, that is, ventilation, 
shading, spraying, etc., so as to keep the temperature variation within 30° if 
possible. In other words, for a gentle spring day, when conditions are generally 
ideal, the house can run from 60° minimum temperature at night to a maximum 
of 80° to 90° during the hottest part of the day with the aid of some ventilation 
and perhaps some spraying of the plants during midday. Temperatures higher 
than 90° F. are not necessarily harmful to the plants if humidity is maintained; 
(3) 
