Mandevilla

Can anyone clarify. I bought a mandevilla climbing vine with Small red flowers. Not knowing at the time that it was not supposedly frost hardy and would only thrive in a conservatory through the winter. I planted this vine 3 years ago against an east facing wall and is quite sheltered. Mulched the ground with chipping and matting. It has survived and is flowering for the first time this spring. What else can I do to make sure it survives, I think I have been very lucky up to now as we had frosts in the winter quite severe although not many. I live in the east of the UK.