Without water a house plant must die. This may take place in a single day in the case of a seeding in sandy soil, or it may take months if the plant has fleshy leaves. But in the end the result is always the same. Because of this obvious fact many gardener beginners give daily dribbles of water, they fail to reduce the frequency of plant watering once winter arrives and they immediately assume that the plant is thirsty whenever leaves wilt or turn yellow. This produces a soggy mass in which practically no house plant can survive. Waterlogging kills by preventing vital air getting to the roots and by encouraging root-rotting diseases. More plants die through overwatering than any other single cause – they are killed by kindness.
Each plant has its own basic need for water. Unfortunately the proper frequency of watering is not a constant feature; it depends on the size of plant, the size of pot, the environment and especially the time of year. Because of this your best guide is observation rather than a moisture meter.
Self-watering pots and devices have a role to play in caring for the Moist At All Times group and for plants when you are on holiday, but they have the distinct disadvantage of not reducing the water supply in winter.
The water to use
Tap water is suitable for nearly all plants. Ideally the water should be stood overnight in a bowl to allow it to lose some of its chlorine and to reach room temperature. This standing period is not essential for hardy plants but it is necessary for delicate varieties. If you live in a hard water area a white crust may develop in time on the surface of the compost. This crust is harmless, but hard water can be harmful to lime-hating plants which are permanent residents indoors. For lime-haters which last for only a comparatively short time in our rooms, the use of hard water will not really pose a problem.
The standard source of soft water is rainwater. Collect it by standing a large, clean bowl outdoors; never use rainwater from a stagnant water-butt.
When to water
Tapping the pot is useless; measuring water loss by estimating its weight calls for great skill. The simplest way of discovering when to water remains the best. Look at the surface – weekly in winter, daily if possible in midsummer. With the remaining plants insert your forefinger in the compost to the full depth of your fingernail. If your fingertip remains dry then the pot needs watering. The most important exceptions are the Cacti and Succulents in winter – if the room is cool leave them alone unless there are signs of shrivelling.
The way to water
The best technique for most plants is to use the quick and easy watering can method as the standard routine and to water occasionally by the immersion method where it is practical.
1. The watering can method – Use a watering can with long, thin spout. Insert the end of the spout under the leaves and pour the water steadily and gently. During the growing season fill up the space between the surface of the compost and the rim of the pot. In the winter stop as soon as water begins to drain from the bottom of the pot. In either case empty the drip tray after about 30 minutes. Never water in full sun as splashed leaves may be scorched. In winter, water in the morning if the room is unheated. Take great care when watering containers without drainage holes – add a little at a time and pour off any free-standing water immediately.
2. The immersion method – Plants such as Saintpaulia, Gloxinia and Cyclamen which do not like water on their leaves or crowns can be watered from below. Immerse the pots in water to just below the level of the compost and leave them to soak until the surface glistens. Allow them to drain and then return the pots to their growing quarters.
Danger signs on plant
1. Too little water – leaves limp and wilted, flowers fall or quickly fade, lower leaves curled, yellow and wilted. Leaf edges brown and dry. The oldest leaves fall first.
2. Too much water – leaves limp, soft and rotten areas, poor growth. Flowers mouldy. Both young and old leaves fall at the same time. Leaves curled, yellow and wilted. Leaf tips brown. Roots brown and mushy.