Propagation/Greenhouse ManagementUnit 1.3 | Part 1 – 147
Supplement 1: Cool- and Warm-Season Greenhouse Management
3:00-4:00: Close all venting and doors half to 1
hour before sun moves off of house. Exact timing
will change as days lengthen.ANTICIPATE—READ AND REACT
n Close the greenhouse earlier when you antici-
pate cold nights. Closing early and the consequent
temperature rise will help retain warmth longer into
the night.
n Be aware of 3–5 day weather forecasts to assist
in venting and watering decisions. Check NOAA
online weather information or other reliable source
to help anticipate what to do and when to do it.
Warm Season Greenhouse Management
As with cool season conditions, maintaining a good
wet-to-dry swing is critical during the warm season.
Ventilation is the primary means to regulate tem-
perature and maintain circulation.
WATERING
In summer, water plants as needed. As a general
cultural practice, water earlier in the day so there is
time for plants to dry down some before the evening
while still having enough moisture to get through
the night. If you are closing on a hot day and plants
have dried down too much, water them as needed.
If it is a plant susceptible to damping off, water
conservatively.
There are 4 main watering “pushes”:
n Morning
n Midday (expect to water through lunch time)
n Mid Afternoon (3:00)
n Evening (5:00) on a HOT day
VENTILATION
Ventilation is the primary tool for cooling, so in
warmer weather it is critical to proactively vent to
keep temperatures from climbing. At its most basic,
warm season venting simply involves opening and
closing at the proper times. The recommendations
below are intended as a guide. Use your senses,
intuition, and knowledge of the current weather
conditions as your primary indicator of what to do
and when to do it.
Typical venting pattern on warm/clear days
(65-75º):
By 8:30 am: Open the ridge vent to 6” and open
sides
By 10:00 am: Fully open ridge vent and leave
door wide open
5:30-6:00 pm: Close all venting and doors,
knowing that temperatures will climb. Be sure
plants have adequate moisture to get through
the night. Be sure all side vents are closed and
turn on HAF fans.
To maintain appropriate temperature on cool,
overcast, or foggy days, venting can begin a bit later
in the morning and may not require the ridge vents
to be fully open, but venting is still crucial to facili-
tate air exchange and prevent the stale/dank condi-
tions that allow damping off organisms to prolifer-
ate and prosper.
Typical venting pattern on cool/overcast/foggy days
(50-65º):
9:00-ish am: Crack ridge vent to 6” and open
side vents
11:00 am: Open ridge to halfway open
12:30-1:00 pm: Open ridge vent fully if inside
temps are >75º
2:30-3:00 pm: Return ridge vents to halfway
open
5:00-5:30 pm: Close all vents. Turn HAF fans on.
Typical venting pattern on hot days (outside temps
predicted to be >80º and no fog):
By 8:00 am: Open side and ridge vents fully.
Keep vents and doors wide open all day
As late as 6:30-7:30 pm: Close ridge and side
vents. Turn on HAF fans.
Consider wetting down the floors to facilitate
evaporative cooling if greenhouse temperature ex-
ceeds 90º.
Based on anticipated weather pattern, consider
moving out all cool season crops, especially lettuces,
brassicas, larkspur, stock, etc. to protect crops from
thermodormancy and other heat-induced stress.