Garden pits, or forcing pits, or pineapple pits (the king of all garden pits, made specifically for the cultivation of the pineapple) could be found in the gardens of the wealthy from the eighteenth century, and in gardens of more modest means during the Victorian age. They could be used for culinary or pleasure plants alike.

Essentially they operated on the same principle as hot beds - tanner's bark or horse manure was used to heat either floors or walls (in the diagram to the left of a pineapple pit the horse manure would have been shovelled into the two trenches to either side of the pit, and the heat allowed to escape into the pit itself via gaps in the brick walls) in order to grow exotic or tender plants. For the flower gardener they were useful in order to force seedlings during the late winter or early spring in order to plant out into the garden when it became warmer.

During the nineteenth century pits (as conservatories and greenhouses) on larger estates were often heated via steam or hot water pipes, which needed a boiler room and some very junior gardener to continually stoke the fire. All but the most wealthy, however, would have used manure or tanner's bark.

Pits would be covered with glazing, which could be opened and closed as necessary in order to ventilate the plants within.

Plants would generally be grown in pots, which, depending on necessity, could be plunged into yet more manure or bark within the floor of the pit, or placed on perforated shelves or trays for drainage.

The size of the pit depended on the size of the garden, the amount of plants that would need to be grown within, and the wealth of the owner.

The only pine pit currently operating in Britain is, I believe, that at the lost gardens of Heligan in Cornwall.

 

Image taken from Charles McIntosh, The Practical Gardener (London, 1828).