Minimum temperature for tropical amaryllids?

Tim Eck
Fri, 24 Apr 2015 05:58:59 PDT
For those in different growing zones, the difference between a frost and a
freeze is probably rather cryptic but it is very important.  A freeze is
mostly what you would expect - the temperature declines below 32 F, often
with winds, overcast or even precipitation.  The higher the winds, the more
severe the damage.
A frost, on the other hand, can occur as high as 40F and requires clear
night skies, very still air, and a flat terrain or a valley.  Even in these
conditions, plants under a tree or other screen from the open sky will be
protected from frost.  Frost damage is caused by radiant heat loss to outer
space creating a micro-clime or surface pool of cold air.  This micro-clime
can be 10F colder than the measured air temperature.  Sloping land, cloud
(or other) cover, or wind will destroy the effect as will a nearby building.
Frosts cannot occur in forests because any heat loss from the upper leaves
is replaced as the cool air drops and is replaced by warmer air.

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