tan heat

Noun

tan heat (uncountable)

1. heat generated by the fermentation of tan bark waste; generally used in horticulture as a source of bottom heat for potted plants in greenhouses; the application of tan heat to greenhouse plants, mainly during the 18-19th century.
   • Many succession [pineapple] plants are preserved through the winter in pits where no fire is kept; these should be managed with great care; a good tan heat is necessary for the principal warmth; good coverings on the glasses should by no means be omitted on nights, and when the weather increases...1771 Thomass Hitt and James Meader: The modern gardener, or, Universal Kalendar
   • Being a native of the West Indies, [Bignonia leucoxylon] does not flourish without the assistance of tan heat; but will live in any situation of the hothouse...1797 Henry Andrews: The Botanist's Repository
2. a bed of tan bark waste used as a source of mild bottom heat for potted plants in greenhouses or hothouses.
   • Bryophyllum calycinum is a succulent plant; it requires very little water, except when growing freely, and the pot to be well drained; it flowers best when plunged in a tan heat; rich loamy soil suits it well.1825 Robert Sweet: The Hot-house and Greenhouse Manual, Or Botanical Cultivator