Hi Liz757, these are not hardy plants, have they been growing outside, or are they in a greenhouse?.
you could scrape a small section of the stem with your thumbnail, if it's green underneath then it has some life, if not it is dead, sorry, Derek.

It is normal for them to lose all their leaves over winter. If you do as Derek advises and you see green, then give the plant a good drink and try to be patient - with warmth it should soon show new shoots (I hope).

Wow, what a coincidence! I bought a growing stem cutting of Bougainvillea a month ago and repotted it the same day and in the process of doing so broke a bunch of its brittle roots! The leaves immediately started to shrivel and yellow and fell over the next few days. I thought it died. I refused to give up. 3 days ago it sprouted green shoots. I was so excited!

I thought this is a pretty hardy plant, no? It can withstand long periods of drought but as I learnt, the root system is extremely fragile.

Hi Chatbud and Liz,

A few years ago we were lucky enough to find Westdale nurseries (near Bradford-on-Avon) who specialise in Bougainvillea. They advised us to allow the plant to dry out between watering in the summer, and then give it a good soak. Btw, they aren't hardy in the UK, so have to be brought indoors in the winter, but so gorgeous it's worth giving them special care!