Normal functioning of any plant depends on water supply. About 70 — 90 per cent of the plant body consists of water, and it is in dilute water solution that the salts essential for nutrition are obtained from the soil. Since the plant only uses about 2 or 3 parts of water for every 1,000 taken in, the rest being passed out through the, it is essential for the plant to get enough and to retain enough, otherwise it will wilt and die of starvation.
Incorrectcan be as harmful as not watering at all, and the gardener must know the right way to water. Evening watering is said to be best for plants grown outdoors, for it reduces loss of moisture by evaporation, but so long as there is no sunshine, watering may safely be done at any time. If for any reason watering must be done in sunshine, care should be taken not to wet the foliage, for wetting increases the rate of evaporation from the , surface, thus accelerating the loss of water and leading to rapid wilting.
Occasional sprinklings do more harm than good by encouraging surface rooting, so that the plants suffer more readily from drought. Give about a watering-canful (2 gallons) to each square yard, which will supply rather less than the equivalent of ½ in. of rain. Use a can with a coarse rose or apply direct from the spout. A can with a fine rose is best employed forbeds or sprinkling and very small plants which merely need overhead damping. If it is impossible to cover all the garden in one day, take several days over the job rather than reduce the watering rate.
Rainwater collected in tubs or barrels is often said to be best, but there is no scientific evidence to support this claim. Unless the tap water is very hard, it may even be better than rain water as the latter can easily be contaminated by harmful substances. However, it is certainly sound economics to collect rainwater. When the supply runs short, tubs etc. should be filled from the tap and the water left to stand for a time to warm up to air temperature. In a large garden, where the hose has to be used, water in the morning so that the water will reach a suitable temperature during the day and notthe plants. On the day after watering, hoe the soil.
If economy in water is essential, give no water at all to drought-resistant plants such as coreopsis, gaillardia, helianthemum, nasturtium, nepeta, succulent plants like, and plants that have deep tap . Water only really thirsty plants such as astilbes, delphiniums, Lobelia cardinalis, Michaelmas daisies, mimulus, pansies, phlox, primulas, and others with shallow and scantily branched systems or large foliage. Lawns must be given a good drenching each time they are watered and it is best to use a revolving sprinkler moved at one hour intervals. In the , more plants fail from incorrect watering than perhaps any other cause. Water at the same temperature as the house should always be used, so keep a tank of rainwater warming up in the greenhouse. Water thoroughly each time, never sprinkle, but take care not to let the soil become waterlogged. Pots should be given individual attention. As a test, rap the sides of sharply with the knuckle, when a hollow ring will indicate need of water and a dull sound a sufficiency. A small wooden hammer can be used instead of one’s knuckles! Cracked pots always give a dull sound. A third method is to lift the pot as wet soil is much heavier than dry soil. Seedlings must be watered with a rose on a can and too much must not be given owing to the risk of damping off, . Dipping boxes and pots to the brim in water is not necessarily better than the conventional method of overhead watering. During winter, watering in the greenhouse must be reduced to the minimum.
Wilting. Unless a supply of water is assured, plants soon wilt and may even die partly or completely.
Wilting is influenced by many conditions besides moisture in the soil. Enough water may be present, but if the soil solution is too concentrated, plants cannot take it in, and water from the cell sap will actually flow out, causing wilting; hence the danger of giving too much fertiliser, particularly to pot plants where the soil is confined. Wilting is naturally more rapid in a dry than in a saturated atmosphere, and in the greenhouse the floor should be watered in very dry weather to prevent the air from losing too much. Temperature also has its effect; if the air is too warm, water is lost more quickly than normally and plants droop readily, as often happens with tomatoes and other plants under glass; but in the evening, when it is cooler, there is less evaporation from the leaf surfaces and the wilted plants are often able to recover. The need for a better adjustment of water supply and temperature is indicated.
When foliage is wetted, the rate of water lost from the plant is increased and plants are more likely to wilt owing to the rapid drying. That is why gardeners should avoid watering plants in sunshine. Care must be taken to distinguish between wilting due solely to lack of water and wilting caused by plants pests or diseases. Insects attacking the base of theor , such as cabbage fly, millepedes, slugs and woodlice will upset the normal functioning of the plant and cause wilting. Damping off of raised in the greenhouse is often preceded by wilting. ‘