Delicate specimens at the Eden Project are being wrapped in fleece, straw and heavy mulch to protect them from frost, and exotic plants such as Proteas, Acacias and Correas are being replaced with more hardy alternatives.
Horticulturist Darren Topps said: "Eden enjoyed exceptionally mild winters for the first seven years of its existence.
"Borderline hardy plants like Pelargoniums, Gazanias and Dahlias all got through the winters no problem – and we were lulled into a false sense of security."
He added: "This is the third year in a row that we have had a prolonged cold spell, with the ground frozen continuously throughout the day."
He said despite the precautions, the cold snap is beneficial to hardy plants and the eradication of pests and diseases.
"The cold gives hardy and native plants a good rest, meaning they tend to flower their socks off the following spring or summer.
"The low temperatures also keep pests and disease in check. And of course the gardens look stunning in frost."