What is the lowest hardiness zone?
Cold Hardiness zones are based on the average annual minimum temperature in a given area of the country, with USDA Zone 1 being the coldest at minus 50 degrees F and USDA Zone 11 the warmest at above 40 degrees F. Zones range from Zone 1 (coldest) to Zone 13 (warmest). USDA zones are based on the average annual extreme minimum winter temperature. Each color represents average coldest temperature in 10°F zones.All of the UK lies within USDA planting zones 6-9. These planting zones are based on average winter temperatures. Few areas in the UK are zone 6, where winter temperatures can drop below minus 17. Celsius. Few are in zone 7, where temperatures drop below minus 12. C.
What is H7 hardiness?
The Royal Horticultural Society has developed a hardiness rating system that classifies plants in accordance with the minimum temperature they can withstand. This rating system runs from hardiness level H7 (plants that can survive temperatures below -20°C/-4°F) to H1a (plants that must be kept above 15°C/59°F). Many indoor plants will see damage when temperatures drop to the mid to lower 40s°F and nearly all will die if exposed to below freezing temperatures.Seedlings, with their tender new leaves, often give up the ghost when temperatures dip to 32-33°F. Tropical plants have differing low-temperature thresholds. Some keel over when temps fall to 40°F; others crumble at 35°F. Other plants are just hardy by nature and can withstand temperatures as low as 18-20°F.Temperatures above 90°F slow down plant growth, and temperatures above 104°F put plants under serious heat stress. A plant under stress does not waste energy blooming—it’s in survival mode.Temperatures below 50°F may stunt their growth for a few weeks, and temperatures below 35° may cause some leaf damage. Freezing temperatures will kill the leaves of most houseplants completely, but the roots typically survive if it was only a short exposure.