In message , JimM
writes
Header says it all really but what does the temperature have to drop to
before you get a 'frost'

Jim

You can get a grass frost with air temperatures (4 feet above ground
level in a screen) as high as 4 or even 5C.

For an air frost, the reading in a screen has to be -0.1C or lower.

Having said that, plants are rarely damaged by a slight grass frost
unless it is prolonged.

Just my opinion of course.

--
Steve Jackson,
Bablake Weather Station,
Coventry, UK
http://www.netlink.co.uk/users/bws