The question ofis a difficult one to answer. Most newcomers to the art of indoor gardening would like to be told that this plant will require once a week, and that one twice, but such directions are impossible to give. They depend on weather, the warmth of the house, the amount and intensity oflight, the quantity and quality of the water, the size and type of the plant and other matters. Watering is really a matter of knowing the plant and this comes only with experience. But it is worth knowing that more plants die of over-watering than any other mistreatment. For this reason it is wise to err on the side of meanness rather than generosity. It is always possible to give a little more water if the plant is seen to be dry, but much more difficult to remove water from a drowning plant.
The most efficient way to water a plant is to submerge the entire pot in a bath or pail of water and leave it there until the bubbles have ceased to rise from the soil surface, an indication that all the air spaces in the soil have been filled with water. If the pot is then removed from the water and stood on one side to drain, water will flow away from theholes at the base of the pot; when water rushes out from one end it sucks air after it through the soil at the top of the pot.
Plants must have air as well as water at the. Giving little driblets of water to the pot from time to time does not encourage this surge of fresh air through the soil, so if the plant cannot be moved to submerge the pot entirely, it is wise to water sufficiently to allow water to trickle through the drainage holes. Leave this excess water in the saucer or other for a couple of hours or so, in case the soil absorbs it again. But if it still remains after this time it should be thrown away, otherwise it will help the plant to drown. If the plant pot is plunged inside another container containing some moisture-retentive material, then any excess water will be absorbed by this and released gently and slowly through the pot to the roots again and to the air in the form of evaporation.
The water requirements of house-plants vary according to the season. Most plants are more or less dormant during the darker days of winter. It is then that they take their rest and at this time they require only sufficient water to keep the soil just moist, no more. If more water is given the roots cannot absorb it and tend to show their rejection by becoming mildewed, even rotten.
There are plants, however, which continue to grow through winter, for example saintpaulias. These plants obviously need more water than if they were dormant but not so much as they would require in summer. There are even one or two plants, such as the vigorous and fast-growing vine tetrastigma, which has reversed seasons and rests during summer, while it grows rampantly during winter. Obviously here too watering should follow the plant’s requirements.