A cold conservatory, which is an unheated greenhouse typically made of glass, helps you raise plants that normally could not grow in your USDA hardiness zone. Because the conservatory can be -12.2 to -6.66 degrees C warmer than outside, plants from up to two warmer USDA zones can thrive. Monitor inside temperatures using a digital thermometer that registers both high and low temperatures over a 24-hour period.
There are more than 800 varieties of camellias, with flowers in a wide range of colours including white, pink and red. The flowers can be single or double. There are many new cold-hardy camellia varieties. Some are hardy down to USDA hardiness zone 6, where the average minimum temperature is --12.2 to -17.8 degrees Celsius. The problem with many of these cold-hardy varieties is they set their buds, but instead flowering in the winter, the buds simply fall off.
Growing regular camellias in pots in a cold conservatory can solve this problem by allowing your to use a less-hardy variety for your zone.
Gardenia thunbergia, an African native, is hardy to USDA hardiness zone 8a, where the average minimum temperature is -12.2 degrees Celsius. It prefers acidic soils, similar to camellia. Although many gardeners in cooler climates could grow gardenias outdoors, choosing these as plants for pots in a cold conservatory makes more sense. The white fragrant blooms will last longer under glass and not sustain the damage they would outdoors. Gardenias can be trained into a small bush or a tree form. They can be grown in full sun, but do better if they are given some shade during the hottest part of the day.
Musa basjoo is a banana plant hardy to USDA hardiness zone 5, where the average minimum temperature is --6.67 degrees Celsius. This banana is a great choice for plants for pots in a cold conservatory. Protected from frost and severe weather elements, musa bajoo is more likely to bloom in a cold conservatory than outside in colder climates because the plant will not die all the way back in the winter. The fruit from musa basjoo will be full of seeds, so the variety is not grown for eating.
- University of California: Center for Landscape and Urban Horticulture: Camellias
- Purdue University: Gardenia: A Gardener's Challenge
- University of Illinois: Hardy Banana -- Musa Basjoo
- "The Complete Idiot's Guide to Year-Round Gardening"; Delilah Smittle and Sheri Ann Richerson; 2010
- The United States National Arboretum: USDA Plant Hardiness Zone Map