How cold can plants tolerate in the greenhouse?
During the autumn and winter, your unheated greenhouse will be beneficial in keeping tender plants frost-free. It will work extremely well as a ‘walk-in’ cold frame for overwintering plants and growing hardy crops. Whilst temperatures outside drop, your greenhouse could stay as warm as 40°F, keeping plants warm and dry.
Depending on the plants age and variety, the temperatures they can tolerate will vary. Whilst most plants freeze when temperatures remain below 28°F for more than five hours, seedlings will often give up when temperatures dip to 32-33°F and tropical plants may struggle at anything below 40°F.
Many hardy plants such as winter vegetables and cool hardy flowers like calendula, chrysanthemum and pansies can withstand temperatures as low as 20-25°F.
Where can I put plants in an unheated greenhouse?
The layout of your greenhouse will indicate where you can put your plants – consider what will grow best in the space you have available.
If you have a soil border, you can sow over-wintering spring onions, spinach leaves and corn salad. Whilst an Alitex greenhouse bench works well for potted plants and keeping more tender plants away from the ground to reduce their exposure to any drafts. High-level shelving, or strawberry boards are perfect for plants that require lots of light.
What type of heater is best for a greenhouse?
In a small glasshouse, less than 161 square foot, with lower temperature requirements a fan heater is probably the most sensible choice.
If size or temperature requirements are greater, then a more complex system is required. We recommend using a convection heating system that works from a hot body in a similar fashion to a radiator system in a house. This provides a gentle convection current around the glasshouse, which is kinder to the plants than blowing hot air at them and drying out the leaves and spreading diseases. The heat can be provided electrically or via a hot water system.
How do you keep a greenhouse warm in the winter?
If you are located in a very cold climate, you may need more alongside your heater to keep your greenhouse warm. By layering old carpet or curtains over the outside, any heat you begin to expel will be insulated. Alternatively, you can use the heater in an isolated area, or LED Grow Lights to target specific plants that require additional support.
Take a look at the Kew greenhouse collection, some of our custom-made greenhouses or the rest of our greenhouse accessories.