Watering Plants in Pots

Watering Plants in Pots

Watering By Hand

Watering can be done by hand or can be made automatic. The object in either case is to keep the roots adequately supplied with water according to the changing needs of the season. Too little water will result in wilting of leaves and a check to growth. Too much water will drive out air from the soil and literally drown the roots, for roots as well as leaves need air for their survival.

When watering with a watering-can each plant can be considered individually. An inspection of the soil may indicate at once whether it is dry but may not be so sure a guide as to whether it is sufficiently wet. Soil in a pot has a deceptive habit of looking damp on top after it has become dry below. One can feel the soil with the finger or lift the pot and judge its weight, for wet soil weighs much more than dry soil. When in doubt, a plant can be carefully tapped out of its pot and examined. All one need do is to turn the plant upside down, place one hand beneath it for support and give the rim of the pot a sharp rap on something firm like the edge of the staging. If it has been well potted in a clean pot it should come out quite cleanly. I do not recommend this as regular practice but it is a useful method of gaining experience. After a while it will be possible to water most of the time by eye alone.

When water is needed, give sufficient to soak the soil right through. If in doubt, wait a few moments after applying the water, then lift the pot and see if water is trickling out of the drainage hole in the bottom. It should be.

Do not splash water on leaves or on the crowns of plants. Some do not mind but some emphatically do and it is wise to get into the habit of watering carefully. Do not use a rose on the can, except for small, newly potted plants, but water direct from the spout. Hold this close to the rim of the pot and use the forefinger to defied the water if necessary.

Automatic Watering

The simplest method of automatic watering is that which uses a capillary bench. This means standing the pots on a bed of wet sand, or a mixture of sand and pea gravel, from which the soil inside the pots sucks up water. The sand can be kept wet in many ways: by allowing water to trickle very slowly over it; by inverting a large water-filled jar at one end with its aperture in a shallow water container about 1 in (2-5cm) below the level of the sand; or by using special feed cups, themselves supplied with water from a tank fitted with a ball valve controlling a mains supply, which means that it can be left for weeks at a time with little or no attention.

Whatever the method of wetting the sand, it is essential that the compost in the pot comes directly in contact with it. There must be no drainage material in the bottom of the pot to break the rise of water. Thick clay pots may need a wick of glass wool through the drainage hole to carry the water up. But with thin plastic pots this should not be required.

Another essential with capillary bench watering is that the compost in the pots should be very porous. If the compost is too close, the soil draws up too much water and there is little or no air left around the roots.

Not all plants thrive on this capillary watering but a great many do, and it is certainly worth trying if it is impossible to give the plants daily attention.

There are other more sophisticated methods of watering automatically and perhaps the best of all consists of very small bore plastic pipes attached to a larger supply pipe. One or more of the small pipes is placed in each pot so that water drips in slowly and the water supply is either turned on by hand or is controlled by a time switch and solenoid valve.

Atmospheric Moisture

Moisture in the air is as important as moisture in the soil. A few plants, notably cacti and other succulents, like a dry atmosphere, but most plants need a fairly moist atmosphere while they are growing and some tropical plants like the air to be saturated with moisture, especially in summer.

Automatic apparatus, known as humidifiers, for maintaining moisture in the air are much used in hospitals and other buildings but have only just begun to be used in greenhouses. The usual way of controlling atmospheric moisture in these is by wetting paths, stages, and even the leaves of the plants themselves if more moisture is required, or by using a little artificial heat and opening the top ventilators a little if the air needs to be dried. This is perhaps the most difficult aspect of greenhouse management to teach. The experienced gardener can tell by the feel of the air on his skin whether it is damp or dry. He is guided, also, by the look of leaves-a slight tendency to lose colour and even to scorch if the air is too dry, a readiness to suffer from moulds and decays if it is too wet. None of this helps the beginner very much but simple meters, knowns as hygrometers, can be purchased to measure atmospheric moisture and one of these hung in the house will at least show what the humidity is at any moment.

What the plants actually need is determined by their state of growth but if instructions are to keep the air ‘moist”, a relative humidity of 90 per cent or more is desirable, if it is to be ‘buoyant’ (a popular expression with gardeners) it should be around 70 per cent and if ‘dry’, 50 per cent or less.

Spraying water on the floor or stages to increase atmospheric humidity is known as damping down. In summer it may be neces-sary to do this two or three times a day to maintain ideal conditions, once early in the morning, again at mid-day and in the late afternoon. Obviously this is impossible for many amateurs who have to be away from home by day. They may try alternatives such as shallow trays of water placed on the floor of the house or a slow trickle of water down the path from a tap. One of the side benefits of capillary bench watering is that the bed of wet sand does help to keep the air moist.

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