Apply mist only during daylight
hours to avoid excessive humidity at night, which
encourages disease. Remember, when the greenhouse
cools at night, the relative humidity will rise
even with the misting system off. Use a 24-hour
timer to shut off the misting system 2 hours
are required during summer to prevent a greenhouse
from seriously overheating, but it is evaporative
cooling from a misting system which
can actually cool the greenhouse to a comfortable
When a greenhouse warms up
and venting begins, essential moisture is lost
with the vented air. Plants lose moisture more
rapidly and begin to wilt. A misting
system can provide needed moisture to maintain
a healthy humidity level of 50 to 70%.
Design for Cooling
& Humidity Control
Use one 2 or 3 gph nozzle
for every 12 to 14 sq. ft. of greenhouse floor.
Install nozzles under the benches to avoid soaking
plants on the benches. Nozzles will operate pointed
in any direction - up, down, sideways or 45°
angle. Control this type of system with a humidistat.
Many foliage plants, tropicals
and subtropicals can be watered and fertilized
by an overhead misting system. Use 2 gph nozzles
installed as high as possible. Control this system
with a short-cycle timer.
Maintain a higher level of
humidity (60 to 70%) for healthier plants. Protect
seedlings and cuttings from fatal water stress.
Imitate orchid's natural environment. Use 1
gph nozzles. Control with a short-cycle
timer: 5 to 10 seconds of mist every 15 to