Taking time to winterize your greenhouse now will help your plants (and
your pocketbook) survive even the worst that Mother Nature sends your
way! One of the first steps in winterizing your greenhouse is heat conservation.
Now is the time to replace broken glass, mend torn poly or damaged polycarbonate.
Caulk as necessary, especially around the foundation. Apply foam tape
to doors and vents to ensure a tight seal. For large gaps use a foam sealant
to stop heat from escaping and insects from getting in.
North walls and solid walls can be lined with one of several different
energy saving materials for maximum insulation and light reflection. If
you frequently have freezing weather, line all but the south wall with
reflective materials such as "Reflectix" or foil insulation.
For sub-zero climates, place this material across the south glazing at
In greenhouses glazed with glass, bubble insulation can provide significant
heat savings. Simply apply to the inside of the walls and roof. Installed
inside your greenhouse glazing, this translucent bubble plastic can reduce
your heating costs up to 45% making it just as effective as insulated
glass. It transmits evenly diffused light through the greenhouse. When
the weather warms up, remove it, roll up and store until needed again.
It has a 3-4 year life span and works well with all types of greenhouse
One of the easiest and least expensive ways you can provide heat is by
using thermal storage. By using a material with a dense thermal-mass,
such as water, brick or rock, you store incoming solar heat. The heat
is then released back into the greenhouse as temperatures drop. Winter
shield materials, usually made of tough, durable poly, act as winter heat
blankets to hold radiant heat in the greenhouse and reduce heating costs
during a cold snap.
What you can grow successfully depends on the temperature you choose to
maintain for your winter greenhouse.
"Cold Greenhouse" (Night temp. 35-45 degrees F)
GROWTH is limited. Some vegetables (such as carrots and Cole crops) mature
in the fall months and can be held over for winter harvest. Simply provide
enough heat to keep the greenhouse from freezing.
"Cool Greenhouse" (Night temp. 45-50 degrees F)
Actively grow many leafy and root crops; e.g., lettuce, cabbage, Brussels
sprouts, beets and carrots. Citrus fruits and grapes can be wintered over
at these temperatures. Automatic heating with thermostatic control is
"Moderate Greenhouse" (Night temp. 55-60 degrees F)
Many options are available, and some plants will propagate. Possibilities
include cucumbers, beans, Bibb lettuce, herbs, strawberries, mushrooms,
cool variety tomatoes, dwarf fruit trees, figs and grapes. (For propagation,
use a heat mat to warm potting mix to 70 degrees for starting seeds and
rooting cuttings. The entire greenhouse environment does not need to be
this warm.) A reliable heating system is necessary and a back up emergency
heater is recommended for protection against a cold snap or power outage.
"Warm Greenhouse" (Night temp. 65-70 degrees F) While
more expensive to heat (we recommend insulated glazing), there are many
unusual and tropical plants you can grow; e.g., lemons, bananas, melons,
dwarf corn, peppers, eggplant and a wide variety of tomatoes. (Additional
light may be necessary in winter.)
It is a good idea to make a checklist of what to do if severe weather
strikes or your greenhouse heater fails. A battery-operated temperature
alarm is essential if the heat goes off in the middle of the night. Keep
a backup heater ready for immediate use. Emergency gas heaters can save
your plants in case of a power outage. These usually require some ventilation.
Another emergency step that can be taken is to drain the household water
heater and place buckets of hot water in the greenhouse. (Water has an
added benefit over other types of thermal mass. If the greenhouse starts
to freeze, the water will freeze first and as it does, it will release
heat. This will give the plants an additional buffer before they start
to freeze.) If freezing is unavoidable: BE SURE TO DRAIN ALL WATER LINES!
Bring rare and sensitive plants into the house if at all possible. Cover
remaining plants with newspapers, or set high-back chairs around nested
plants and cover with blankets.
Jack Frost is planning to visit many greenhouses this winter. With good
equipment and thoughtful planning you can send him on his way, and enjoy
your indoor garden all winter long!