Botanical Cell

A botanical cell is a planting bed built into a dwelling behind glass, so that ground inside the house grows food. Sitting within the heated shell, it carries salad and herbs through the cold half of the year and keeps tender perennials such as banana, citrus and fig alive where they could not survive outdoors. Daylight through the glazing is the one thing that cannot be substituted: a bed without it is a container of dying plants, so a cell is designed around its glazed wall rather than fitted into a spare corner.

Two things are often claimed for indoor planting that one bed does not deliver. Cleaning a room's air this way would take something like one plant for every 0.2 square metres (2 sq ft) of floor, because the experiments behind the claim used small sealed chambers, not rooms that trade air with outside. Humidity is the same story: water evaporating from one bed spreads through the whole room and barely moves the reading, though a built-in bed has far more open soil than a pot and sits between a houseplant and a real humidifier. Water can come from a tank by gravity or from household wash water; either works, and it is a choice rather than a requirement.

Too much moisture rather than too little is what goes wrong. Indoors the safe band runs from about a quarter relative humidity in the cold season to half in the warm one, and past that come condensation and mould; a wet bed in a sealed house pushes toward that ceiling in exactly the season the house is shut. The same damp breeds fungus gnats, and the cure is watering less. Water to demand, let the surface dry between waterings, vent through the closed season, and read condensation on the glass as the first warning. A bed fed on wash water has one slower failure: sodium builds up, displaces calcium from clay and seals the soil over years unless the medium is leached or low-sodium soaps used.