Give Your Plants The Humidity They Need – Cold air requires only a small amount of water vapor before it becomes saturated, and so on an average winter day the air is moist. When you turn on a radiator to warm up this cold air, its capacity to hold water vapor is greatly increased. As the room becomes comfortable the amount of water vapor in the air is no longer enough to keep it moist. The air becomes ‘dry’; in technical terms the relative humidity has fallen.
Central heating in the depths of winter can produce air with the relative humidity of the Sahara desert.
Very few indoor plants actually like such conditions; many foliage plants and most flowering plants will suffer if you don’t do something to increase the humidity around the leaves. You can, of course, avoid the problem by finding a moist home for your plants – the kitchen, bathroom or a terrarium, but the living room atmosphere will be dry. You can use a humidifier to increase the moisture content of the whole room, but it is much more usual to use one or more of the techniques
below to produce a moist microclimate around the plant whilst the atmosphere in the rest of the room remains as dry as ever.
Misting. Use a mister to deposit a coating of small droplets over the leaves. lt is best to use tepid water and under cool conditions do this job in the morning so
that the foliage will be dry before nightfall. Cover all the plant, not just one side, and do not mist when the foliage is exposed to bright sunlight. Misting does more than provide a temporary increase in humidity; it has a cooling effect on hot sunny days, it discourages red spider mite and it reduces the dust deposit on leaves.
Grouping. Plants grown in pot groups and indoor gardens have the benefit of increased moisture arising from damp compost and the foliage of surrounding plants. The air trapped between them will have an appreciably higher relative
humidity than the atmosphere around an isolated plant. The best method of raising the humidity is to use a pebble tray. There is a danger of too much humidity when
grouping plants together – make sure that there is enough space between them.
Double potting. Use an outer waterproof container and fill the space between the pot and the container with moist peat. Keep this packing material thoroughly and continually moist so that there will always be a surface layer of moisture to evaporate and raise the relative humidity. Double potting does more than raise the humidity – it provides a moisture reservoir below the pot and it insulates the compost inside the pot from sudden changes in temperature.