(botany) A plant which requires protection against frost.
It is grown in conservatories for half-hardy plants.
For tropical plants the heat of a propagating house-75° to 80°, with a bottom heat of 80° to 90° - is desirable, and in many cases absolutely necessary; for others, such as half-hardy annuals, a mild hot bed, or a temperate pit ranging from 60° to 70°, is convenient; while of course all outdoor crops have to submit to the natural temperature of the season.
Annuals may be divided into three classes: the hardy, which are sown at once in the ground they are to occupy; the half-hardy, which succeed best when aided at first by a slight hot bed, and then transplanted into the open air; and the tender, which are kept in pots, and treated as greenhouse or stove plants, to which departments they properly belong.
Some of the more popular annuals, hardy and half-hardy, have been very much varied as regards habit and the colour of the flowers, and purchases may be made in the seed shops of such things as China asters, stocks, Chinese and Indian pinks, larkspurs, phloxes and others, amongst which some of the most beautiful of the summer flowers may be found.
The half-hardy series are best sown in pots or pans under glass in mild,heat, in order to accelerate germination.