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.
1771 Thomass Hitt and James Meader: The modern gardener, or, Universal Kalendar
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 with cold, let the outsides of such pits be well lined with litter to the top. If the heat of the bark bed is but moderate, let some hot dung be applied all round to keep out the cold and augment the warmth within side...
1797 Henry Andrews: The Botanist's Repository
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...
a bed of tan bark waste used as a source of mild bottom heat for potted plants in greenhouses or hothouses.
1825 Robert Sweet: The Hot-house and Greenhouse Manual, Or Botanical Cultivator
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.
