Drought

Saving water and efficient watering

By Bridgette Saunders

Less than 3 percent of the annual water consumption of an average household is estimated to be from garden use, but at peak demand as much as 70 percent of water supplied may be used in gardens. This rush in demand can lead to water companies being forced to deplete groundwater and streams, which can cause serious environmental damage as well as raising the cost of water for customers. Allotment holders should therefore use mains water as sparingly as they can.

Even in dry areas, 24,000 litres (5280 gallons or 150 water butts) could be collected from the roof each year. However, most water falls in winter, and would have to be stored for use in summer. There are about 18 weeks from May until September when plants' needs exceed rainfall. At first, the shortfall is met from soil reserves, but these can peter out by July, leading to about six weeks when watering is needed. This year we have already reached that point and so harvesting water is essential.

• Vegetable yields and quality will be improved by watering at times when drought stress would affect the part of the plant that is gathered. Leafy crops such as lettuce and spinach should never be short of water. Onions require little or no watering. Most other crops need watering at sowing and transplanting time, and then again as the fruits, roots or tubers are developing. It is also a good idea to give a single, thorough watering about two weeks before harvest.
• Mulching with a layer of organic matter or wood chip at least 5cm (2in) thick, or using landscaping fabric such as mypex, reduces moisture loss from the upper layers of the soil. This may amount to as much as the equivalent of 2cm (0.75in) of rain. Mulch will also suppress weeds whose rapid growth means they compete with your vegetables and flowers for water.
• Planting new plants between autumn and spring gives them the best chance of growing roots before dry weather begins.
• Loss of water from leaves varies with temperature, soil moisture and the time of day, but wind can also quickly draw water out of plants. The best time of day to water is in the evening when there will be less evaporation.  A thorough soaking twice a week is much better than a little every day because thorough watering will enable to roots to develop lower down. On sloping sites it is difficult to water new plants without moisture running down over the surface.  It may be best to terrace severe slopes. 
•  A windy site can be divided into sections with boundaries.  Hedges are great as they filter wind, reducing moisture loss, but also, being a living plant, they also take up water. You can make woven willow hurdles as they are also semi-permeable, and do not take up valuable water.  Temporary wind breaks such as double rows of chicken wire stuffed with straw can be used to protect vulnerable plants from the drying effects of wind.

Below is a guide to which vegetables need watering when:

The amount of water needed by the crop depends on which part of the plant is eaten.

Legumes - Broad beans and peas need lots of water at flowering time in order for pods to set and, again, two weeks after flowering begins. As young plants, avoid too much water as this can encourage leafy growth and reduce the yield. Runner beans need constant moisture for pods to set, whereas French beans are less sensitive to some dryness.

Stem vegetables - Celery, celeriac and Florence fennel need water during growth. Periods of drought stress are very damaging and should be avoided – it can lead to bolting or poor quality crops.

Curcubits - Courgettes need constant moisture all the way through to harvest. Marrows, pumpkin and winter squash benefit from watering but, in practice, often produce fair fruits from minimal watering. Trailing types need less water as their spreading habit conserves moisture and the stems root where they touch the ground.

Fruiting crops - Aubergines, sweet corn and tomatoes all need watering well to aid establishment and also at throughout the flowering and fruiting period.

Leafy crops - Cabbages, chards, lettuce and all salad crops need water at every stage of growth. If water is especially short, make sure that you soak the ground around cabbages and lettuces when hearts begin to form.

Root crops - Carrots, beetroot and parsnips require watering before the soil becomes dry, for example, if there are 14 days without rain. Onions, shallots and leeks need only to be watered when they are establishing, and in very dry spells. Potatoes benefit from being watered every 10-14 days once the tubers are marble-size. Radishes need to be watered every week in dry spells

Finally collect as much rain water as you can – using as many containers as possible.  You could build a simple shelter using four posts and some onduline for the roof and put up some guttering to collect water. Make sure you have watering cans to hand and filled to save your back.