Vegetables are quick-growing crops compared to trees and shrubs, and consequently, need regular watering, This ensures that all stages of development, from seedling to mature crop are unchecked. The result of providing the right amount of water for crops will result in better crops and healthier plants.
Timing On planting and dry spells
Difficulty Easy, moderate or difficult
When to water vegetables
Vegetables need varying amounts of water depending on the stage in their life, the type of plant and the texture of the soil. For a general guide, the following may help:
- Freshly sown seed and young vegetable plants need adequate water. Water the seed drill before sowing. Watering afterwards can create a cap (hard crust) on the soil
- Once plants are established and putting on growth, at the least, water when drought will affect the part of the plant that is to be harvested. In practical terms, watering about two weeks before harvesting is usually sufficient
- On drought-prone sandy soils or sticky clays, water every 10-14 days in dry spells
Which crops need watering when?
The amount of water needed by the crop depends on which part of the plant is eaten.
- 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
- 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
- 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
- Aubergines, sweet corn and tomatoes all need watering well to aid establishment and also at throughout the flowering and fruiting period
- Cabbages, chard, 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
- 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
How to water vegetables
There are definite techniques to learn if watering plants is to be done efficiently and effectively. This holds true for watering vegetables;
- The key to watering successfully is to water thoroughly to a depth of 30cm (1ft). Avoid watering the top centimetre or so on a daily basis, for example. Watering every 10-14 days (if there is no rain) is a general guide
- Dig down to a spade’s depth to see if there is moisture in the soil; if so watering is unnecessary. Bear in mind that sandy soils can look dry but still contain moisture and clay soils can look wet, but the water is held too tightly for plants to access
- Watering when the plant does not need it can increase the growth of the plant, but not the size of the part that is to be harvested
- Keep vegetable-growing areas free of weeds. A surprising amount of moisture can be taken from the soil by weeds
Vegetables in containers
Any plants in containers can quickly become under stress as their roots are unable to search for further moisture and nutrients.
- Consider using drip irrigation to keep water thirsty crops such as courgettes and tomatoes supplied with the water they need
- Avoid using only peat compost; if it dries out too much, it can be very difficult to re-hydrate. Try peat-substitutes based on green waste and composted bark or mix with a loam-based compost such as John Innes No 3, which will hold moisture more efficiently
How to reduce watering
Watering plants is time consuming but, by setting up water-efficient systems early in the season, you can enjoy more of the summer picking and eating your produce.
- Make sure your soil has had plenty of organic matter dug into in. Garden compost, well-rotted manure and green waste compost are all useful
- Double digging and adding organic matter on some soils (ie sand and poor loams) may improve texture and water retentive qualities
- Most crops can be planted through a layer of semi-permeable landscape fabric to conserve water and control weeds. This is especially useful for the onion family, which will not tolerate weeds. Potatoes grow well in this way and do not then need earthing up. To supply water, set up irrigation underneath the membrane (eg leaky pipe) or water carefully with a sprinkler. Water will gradually sink in
- For widely-spaced vegetables such as tomatoes, mulch underneath after watering or rain with a 5-7.5cm (2-3in) layer of garden compost or well-rotted manure
- On very dry soils, use planting techniques such as planting transplants a little lower than the surrounding soil so that water collects in the ‘puddle’ and actually sinks in
Although watering sounds like a simple task, supplying just right amount can be a challenge.
- Too little and plants can be prone to bolting, powdery mildew and nutrient deficiencies such as blossom end rot in tomatoes
- Too much water can cause leafy growth, which is great for lettuce, but not for root vegetables such as carrots which can split
- Overwatering can exacerbate slug and snail problems and encourage foot and root rots
The Royal Horticultural Society is the UK’s leading gardening charity. We aim to enrich everyone’s life through plants, and make the UK a greener and more beautiful place.