For healthy growth all but desert cacti, succulents and snake plants need relative humidity in the vicinity of 40 to 50 per cent. This will not cause dampness of furnishings but is about the same as we need for healthy, comfortable living.When air is heated in an enclosed room, the relative humidity drops considerably, in some cases to less than half that of the unheated air. This low humidity occurs in closed rooms which have sun on large areas of glass, or with room heaters. The result is poor growth, lack of foliage and lustre, brown tips or edges on the leaves. It can affect flowering of African violets or cause flowers to become limp prematurely.

The effects of low humidity can be off set to some extent by keeping your plants well away from heaters and by grouping them together so that evaporation from soil and foliage forms a more humid micro-climate around them. Better still, place moist material below them, or use the old trick of standing them on a tray of pebbles with sufficient water in the base to keep the pebbles damp without it touching the clots.