Watering Plants and Garden Irrigation
Watering Plants and Garden Irrigation
Rainfall is often insufficient to supply the garden with all the water it needs. Plant survival depends on water.
Few plants survive for very long without water — even desertand , which store water in swollen stems and leaves, need a long drink from time to time. Temperature, condition and wind also influence each plant’s water requirements.
Not only must the frequency of watering plants be regulated to suit your individual plants, but the quantity supplied at any one time, together with the droplet size, should be correctly adjusted. Excess water causes waterlogging, which is as bad for plants as drought. Under waterlogged conditions oxygen cannot reach the roots, which suffocate, killing the plant.
Insufficient water results in retarded growth. Plants can absorb nutrients from the soil only in solution with water, so they not only dehydrate in dry soils, but starve as well. In dry conditions leaf pores close to restrict water loss from the plant. In so doing, carbon dioxide intake is limited and in turn the plant is less able to manufacture sugars — food — so growth subsequently suffers.
It is essential to wet the soil deeply enough to reach the plant roots. Frequent but insufficient watering merely dampens the soil surface — it does not penetrate to the soil layer where most roots are formed. It is better to water thoroughly once or twice a week than to give a little water several times a week. Even under drought conditions, a lot of water applied once a week is still the best remedy.
Before using mains water in the garden, check with your local water authority — by law, you may have to pay an extra licence fee. Even then, there may be permanent restrictions on the use of certain watering equipment, or temporary restrictions during periods of water shortage.
Newly planted outdoor plants and all shallow-rooted plants, such as beddingand vegetables, are at the greatest risk from water shortage. Plants grown close to a high wall — within 60cm (2ft) — are also vulnerable, but all plants, however deep their roots, can be affected by drought.
Slow-growing plants, such as many trees and shrubs, need regular watering during the growing season for a couple of years after planting. Some flowering plants, however, produce a better show when kept on the dry side — moist conditions encourage leaf growth, but few flowers. These include nasturtiums (Tropaeolum majus) and or Livingstone daisies (Mesonbryanthemum criniflorum).
Salad vegetables need a lot of water to grow quickly and be sweet and tender when picked. If lettuces or, for example, are too dry they quickly ‘go to seed’ — forming flowers and fibrous, tough growth. Excessive watering, however, can reduce the flavour of vegetables, so a balance must be achieved.
Container plants must be watered frequently. Hanging baskets are especially liable to dry out in sunny weather, and ceramic / terracotta pots lose water faster than plastic ones.
Sandy soils and those which are low in organic content dry out fast, while clay soils hold most water but quickly become waterlogged. Well-balanced loam holds a good quantity of water and is also open-textured and more resistant to waterlogging.
The long-term use of inorganic fertilizers can also hinder water uptake from the soil. Where possible, use organic fertilizers.
When spraying water, large droplets or high pressure break down the soil surface into a slurry. As this dries, a surface ‘cap’ forms which blocks the entry of subsequent water and chokes out air. On a slope, large droplet size or rapid application of water also causes erosion — valuable topsoil washes to the bottom. Good watering equipment should deliver a fine spray, or be adjustable.
When to water
Foliage becomes dull when water is lacking. This is the correct time to apply water. If you wait until leaves and stems wilt the plant will suffer. Another test is to check the soil moisture content 5-10cm (2-4in) below the surface. Dig a small hole with a trowel — the soil at the bottom should be moist to the touch and darker than the surface soil.
The amount of water needed to restore the correct soil moisture level varies considerably. Small shrubs may need about 5 litres (1 gallon) per plant and a tree may need 20 litres (4 gallons) or more. Smaller plants are best given an overall watering, about 10-20 litres (2-4 gallons) per sq m/yd.
Whendelicate — including vegetables — set them in a shallow depression rather than level with the surface, firm in very gently, then water in with a watering can until a puddle forms in the ‘well’.