Plastic films can be made of polyethylene (PE), polyvinyl
chloride (PVC), and copolymers of these materials.
Polyethylene will last one to three years, while PVC and
copolymers with UV inhibitors will last longer.
Heating and Cooling
To control the temperature in your greenhouse, you’ll need to
install heating and cooling systems. For most plants, night
temperatures of 55-65˚F and a maximum daytime
temperature of 85˚F will do. If you simply want to
protect your plants from frost, then setting your
thermostat to 40˚F will be adequate.
Remember to account for the microclimates
within your greenhouse. The spaces near walls,
the floor, ventilation, and any kind of opening will
be cooler than the rest of the area.
To heat your greenhouse, you can use a space
heater, hot-water or steam system, electric heater,
forced-air heater, or radiant heat lamps above
plants. A space heater with a few circulating fans
is an inexpensive option for smaller greenhouses.
Arguably the most efficient system for small
greenhouses is a forced-air furnace that distributes
heat through ducting or a plastic tube system. The
tube is placed as high as possible down the length
of the greenhouse to distribute heat evenly so
there are no cold spots.
To cool your greenhouse, you can use evaporative
cooling systems, fogging and misting systems, or
shade cloth. Evaporative cooling and fogging systems both
increase humidity and work well in drier climates. If your
humidity gets higher than 90 per cent, your plants will start
having issues and you should bring in a dehumidifier to bring
humidity back down between 70 and 85 per cent.
Evaporative cooling systems, also known as swamp coolers,
pass hot air though a soaked screen or spray of water to cool
it down. Foggers and misters work well, however, can be high
maintenance when emitters clog.
Shading your greenhouse will also bring the temperature
down. Trees planted on the south side will offer afternoon
shade. You can also use a shade cloth, roll up screen, or paint
a compound directly on the glass.
Greenhouse Ventilation
Proper ventilation is essential in your greenhouse. It
circulates the air and keeps the temperature even. It also
exchanges the stale air for fresh air and replenishes CO 2 .
Vents, intake and exhaust
fans, and oscillating fans will
create enough air flow for a
healthy environment.
Without air flow, warm air
would rise to the top of the
greenhouse and cool air would
settle at the bottom.
By placing fans in diagonally
opposite corners, you will move
air in a circular motion and keep temperatures uniform
throughout the greenhouse.
Intake and exhaust fans work together to exchange stale air
for fresh air. The fans you choose should be powerful enough
to change the air about once per minute.
Vents are helpful when moving air. When the warm air rises
and escapes through the roof vent, cool air will be drawn in
through the side vents.
"Automate everything. If you don’t, you
will be tied to your greenhouse, opening
and closing vents throughout the day and
hand watering all of your plants daily. "
Automation
Now that you have all the pieces in place, do yourself a favor
and automate everything. If you don’t, you will be tied to your
greenhouse, opening and closing vents throughout the day
and hand watering all of your plants
daily. The more money you invest in
automation technology, the easier
your life will be.
You can hook your heaters, cooling
system, fans, and vents up to a
thermostat that will turn them off and
on depending on the temperature.
Humidistats will regulate humidifiers
and dehumidifiers to keep your
humidity levels in check. Automatic watering systems will
ensure your plants never get too thirsty.
“REMEMBER TO
ACCOUNT FOR THE
MICROCLIMATES
WITHIN YOUR
greenhouse.”
32
Maximum Yield
A greenhouse is a wonderful addition to any garden. Though
it can be costly up front, once it is set up and automated it will
extend your growing season, give you space to propagate, and
allow you to grow tropical plants you may not have been able
to grow otherwise.