One of the most vulnerable times for a greenhouse is a winter night. So, as fall winds down, the need for heat increases. Without the sun, we can’t expect the greenhouse to have any solar gain to keep it warm. This article includes some strategies to help keep your winter greenhouse warm.
Place containers on a pallet so they aren’t in direct contact with the ground. Add a natural gas or propane heater, as they are more efficient forms of heat compared to electric. Unit heaters or direct air fired heaters can help warm up the air and melt some snow accumulations if needed, but the plants themselves might still be inadequately heated for proper growth since only 40-60% of the heat reaches the plants.
The best method for getting 95% of the heat concentrated to the plant is through the root zone. Heated floors like concrete and even gravel can be more efficient than the direct fire unites. When using floor heat, it’s best to keep the containers on the ground and skip the pallets so the roots are closer to the heat source. If growing on benches or tables, it’s best to run heated lines under the benches to get the heat where it needs to be. We’ve heard up to 40% yield decreases when only using direct-fired heaters. So we look to the root zone heat first and direct-fired heaters secondarily. The heating system runs very efficiently by circulating warm water through tubes placed in the ground or under the benches.
Another strategy for extending the seasons rather than going all winter and requiring a heating system, would be to keep the winter greenhouse closed and exhaust fans off in the morning until the greenhouse warms up. Greenhouses on a cold winter day can reach as high as the 90 degrees without hurting anything. This helps warm the soil from the previous cold night. Once the house gets warmed up for an hour or so, the ventilation can be used. Either mechanically or passively, you only want to cool things down a bit or stabilize those interior temps until just before evening. Closing and/or turning off the ventilation system around 3:00pm will help encourage some solar gain before the sun goes down. Get the greenhouse up to the high 80s to low 90s until it gets dark, as warmer soil/plants have a better chance of making it through the chilly night.
Call or e-mail for more information and tips on how to maintain a winter greenhouse.
(530)273-5483 or firstname.lastname@example.org