It depends which bulbs, Guest - some summer flowering bulbs are tender and will be killed by frost - those that should be lifted in the autumn, like Gladioli, Acidanthera, Ixia, Sparaxis, Zephyranthes, Calla etc.

Narcissi and tulips etc in the ground are hardy and should be fine. In pots, it's wise to wrap bubble wrap round the pots in very severe weather - to protect both bulbs and the pots!