Many of the cool-season annuals like Shirley poppies or small violas that
have been recommended as companion plants don't work very well in the
South. They burn out early and may not come back..
Summer hardiness is as important as winter hardiness. Plants are able to
make only so much food for themselves during the day. It has to get them
though the night and also provide enough for growth. But plants'
metabolism is regulated by temperature. If the nights are consistantly
warm, too much food is used up during the night and the plants may not be
able to grow--they may not even be able to "make it through the night," and
so slowly dwindle away. This is why numbers of plants popular in England
and New England don't do at all well in the South with its warm nights.
Yet garden centers here continue to stock these cool-night annuals and sell
them in the South. People plant them and they do fine until warm nights
arrive. Then they decline and look awful if they don't outright die.
Arise, oppressed southern gardeners! Demand heat-tolerant plants!
Department of Biology
Hampden-Sydney VA 23943