As a rule of thumb at this time of the year, a night without cloud cover could result in a frosty morning, usually if there are clouds about you could be lucky and not have frost. Well that's my theory,which seems to work for me when early night temperatures are around 5 degrees.
Photo - davesgarden.com
Those of you with glasshouses might just survive the frost slightly better as these structures do tend to remain very slightly warmer than a poly-tunnel. You could also line your greenhouse walls with bubble wrap, this will offer extra protection, but you will loose a little light but well worth the compromise.
Frost protection with fleece
A little fleece goes a long way, I managed to just about cover all the plants in my poly-tunnel last night for 10 euros, so well worth it. So make sure you indoor crops are protected, tomatoes really cannot take any frost, they will die instantly as I found out last year at my own expense. The fleece might not protect against a heavy frost but fingers crossed it will save my plants from the light frosts we have been having here in Brittany.I have decided to create a new Facebook Page for Mr Tomato King, please pass by and give us a like.