Here I am in zone 8b, but with most of my roses lacking
canopy cover (it gets in the way of the Florida sun), a
light frost can be somewhat intensified by heat radiating
off into (ultimately) outer space on cold, clear nights. The
first light frosts have already hit, turning the banana trees
to dark mush, blighting the cannas and the lemongrass. The
roses are still putting out new growth, however, and seem
not to have been affected, but sooner or later there'll be a
20-F dawn. Should I invest in frost cloth, or simply let the
new growth be frozen the way it was last year? That seems
not to have crippled or killed any rosebushes, but this time I
have more tiny plants that were cuttings only months ago, with
half their volume or more still tender. What would you do?

(18 to 20F is about as cold as it gets here in a typical winter,
with temperatures typically well above freezing before the
following noon, and if I can keep these little plants (still mostly
in pots) from losing their new growth, I might be glad of it later.
The 8 degrees F or so of protection the cloth can provide might
suffice to do just that.)

Mark., from icy, icy North Florida