Despite vegetables being largely made up of water and therefore very vulnerable to poor results in dry soil there is scope to grow vegetables in ways that make the best use of water possible.
Digging in two bucketful of organic matter such as well-rotted manure per square metre will add to the water-retaining capacity of the soil. As much as two weeks moisture for subsequent crops can be retained, as well as adding sufficient nutrients for good growth.
Cultivating soils after the beginning of April leads to severe moisture loss. Better to loosen any compaction by wiggling a fork and scratching a seedbed with a light hoe.
Fertilisers are very helpful in droughts. Adequate nutrient supply allows plants to make the most efficient use of available water. However, adding excessive quantities brings no extra benefits and may damage crops and the environment.
Sowing and spacing
Sowing early, before May where possible, will allow crops to root out into moist soil before severe drought arrives. Drought stress becomes severe in most dry years from June. This is especially applicable to crops such as carrots that will stand in the ground until ready to use, but less useful where successional sowings of spinach or salads for example are needed for continuity of supply.
Later sowings, typically after May, might have to be made into dry soil. Where this is the case applying water down the drill (groove cut in soil) before sowing is a water efficient way of ensuring good germination.
Successional sowings might be problematic if the soil is dry in mid-summer. Consider sowing more early crops and freezing or preserving the surplus for use later.
Spacing plants more widely, usually by about 50%, allows each plant a greater volume of soil to explore for water and therefore more drought resistant, at the cost of reduced overall yield. An example of this are cauliflowers planted at 30cm intervals in rows 45cms apart where irrigation is available, and at 45cm intervals in 60cm rows where water is unavailable.
Carrots, beetroot, parsnips and other root crops are relatively drought tolerant. Salads and other leafy vegetables are particularly vulnerable. Plants that set fruit or pods are most vulnerable at flowering time. Examples include peas, runner beans and sweetcorn.
Vegetables vary in their ability to cope during a drought;
- Carrots, beetroot, parsnips and other root crops are relatively drought tolerant
- Salads and other leafy vegetables are particularly vulnerable
- Plants that set fruit or pods are most vulnerable at flowering time. Examples include peas, runner beans and sweetcorn
- Peas and onions have notably poor roots and low yields must be accepted where drought occurs unless watered
- Amongst brassicas cabbage and calabrese are less vulnerable than Brussels sprouts and cauliflowers, while turnips are notably deeper rooting and more drought resistant than swedes
- Chicories, endives and chards are likely to require less water than lettuces or spinach
- There is usually not much information on differences in drought tolerance between cultivars. An exception is potatoes where some cultivars are notably better at using water; ‘Desiree’, ‘Marfona’ and ‘Robinta’ for example
Growing baby leaf crops of salads such as lettuce, chicories, endive and oriental greens in a small area is a more efficient use of water and space than growing more widely spaced heading crops on a larger area.
Where drought is expected and watering is not possible consider planting more early crops, broad beans for example, and freezing or preserving produce for use in late summer.
Weeds consume large quantities of water and a high level of weed control is especially valuable in periods of dry soil.
Areas of bare soil awaiting planting can be kept covered in black plastic until needed. Carpets are no longer recommended for use in vegetable gardens as it is unclear if the glues used in their manufacture are environmentally benign.
Often there is the opportunity to mulch soils around widely spaced crops such as tomatoes or courgettes either using organic materials such as mushroom compost or black plastic sheets. This will control weeds and prevent loss of moisture from the soil surface.
Any soil disturbance will lead to moisture loss, but weed control by very shallow hoeing is usually acceptable. The old practice of frequent hoeing to create ‘dust mulches’ is no longer thought to be effective.
Flameguns can be used between rows to scorch off weeds but this is not easy, especially as the crop grows.
Elimination of weeds by approved contact weedkillers will conserve moisture but care is needed to accomplish without damaging crops.
Weedkillers for gardeners (Adobe Acrobat pdf document outlining weedkillers available to gardeners) – see section 3
Water loss is especially severe in windy weather and shelter from winds will help slow loss of moisture from crops.
The use of insect proof mesh to cover carrots and parsnips to exclude carrot fly and brassicas to keep off cabbage root fly and caterpillars will reduce airflow over plants and thus conserve moisture. Similarly fleece covering of warmth loving crops, courgettes for example, to provide hotter growing conditions will also help conserve moisture in breezy weather.
Long term planning
Established permanent crops are less susceptible to drought and devoting a larger proportion to soft fruit, rhubarb, globe artichokes and asparagus is worth considering.