Yes. An unheated greenhouse can drop below freezing on clear winter nights, and nutrient solution freezes at close to the same temperature as water. Frozen solution damages roots and can crack containers.
Why Greenhouses Still Freeze
A greenhouse traps heat during the day, but glass and plastic lose it quickly at night, especially when the sky is clear. On the coldest nights the inside can be nearly as cold as outside.
Protecting Containers
- Move containers off the floor, which is often the coldest spot.
- Group them together; a cluster loses heat more slowly than spread-out containers.
- Wrap containers or cover plants with fleece on frosty nights.
- Large containers hold heat longer than small jars.
- On the coldest nights, bring small containers indoors.
What to Grow in the Cold Months
Cold-tolerant leafy greens are the best choice for a winter greenhouse. Growth slows down a lot in short, cold days, so expect harvests to take longer.
After a Freeze
If a container froze, let it thaw slowly, then check the roots and the container for cracks. Plants with mushy, dark roots are unlikely to recover.
Related guide: growing Kratky in a greenhouse.
