Either water in the morning or the evening, allow plants to soak up moisture before the hottest part of the day.

Target the part of the plant that needs water. This means watering the area of the soil above the roots, but don't saturate, because some of the water will evaporate or run off.
Watering plants less frequently, but more thoroughly helps them to develop deep root systems that are better equipped to seek out moisture in the soil.
Fit a water butt and save hundreds of litres of rainwater in wet periods to use when your garden needs it most.

Too Much Water

While lack of water isn’t good, neither is too much water. Over watering can promote disease and encourage slugs and snails. It can also compact soil and wash away minerals. Too-frequent watering promotes shallow roots, making plants less drought-resistant. Deep roots seek out water during dry spells and are more resilient. One sign that your plants are getting too much water is yellowing and droopy leaves.

Time of Day to Water

The best time to water is early morning. This is especially good in warm weather as it protects the plants from drying mid-day sun and keeps them from wilting. If you can’t water in the morning, the next-best choice is late afternoon, so that plant foliage can dry out before sunset. Wet foliage overnight encourages fungal disease, a risk especially in damp climates. Don’t water in the middle of the day when the sun is the hottest. This not only wastes water due to rapid evaporation, but hot sun on wet plants can damage leaves and fruit.

How Often to Water

Water deeply and less often, rather than watering a little more frequently. One suggestion is to water an established garden every six to ten days, watering 15-30 cm (6-12 inches) deep, in the absence of adequate rainfall.

The best way to determine if water is needed: use a trowel and dig into the soil. If the soil is dry to a depth of 15-30 cm (6-12 inches), it’s time to water. Water to the depth of the plants’ roots, as outlined above.

Drooping plants are an obvious sign it’s time to water. If your plants are wilting, you’ve waited too long - a wilting plant is under stress. But drooping leaves may also be a sign of insect infestation or disease. If your plants are still drooping after a good soaking, lack of moisture may not be the problem.

Watering by Stages of Growth

Plants need water for photosynthesis and respiration, as well for absorbing nutrients. For vegetables, watering is more critical at some stages of the plant’s development than at others.

Seeds and seedlings need diligent watering. Newly-seeded beds should be moist but not soggy. Water with a fine mist to avoid washing away seeds.

Transplants should be watered thoroughly after planting, especially important during dry weather. Plants can experience shock due to root damage when transplanting: a good watering helps them adjust.

Many vegetables need special attention to watering during two periods: when they’re flowering and when fruiting. A critical time for watering legumes, sweet potatoes and sweet corn is when plants are flowering (in the case of corn that means when the tassels and ears are forming). A critical time for watering tomatoes and squash is when their fruit is developing. When peas and beans are forming pods and sweet corn ears are filling out, they need attention to watering as well. Leafy greens and roots require steady watering throughout their growth.

With root crops, be careful not to give them too much water, which promotes leaf growth but hinders root growth and can also cause roots to split.

Vegetables that produce edible fruit, pods and seeds also shouldn’t get too much water before they flower. This results in lots of leaves and shoots, but fewer flowers and consequently, lower yields.

Conserving Moisture

Conserving water is not only good for saving money, it’s also good for the environment and saves time spent watering. One way to conserve moisture is by using mulch. A layer of compost, well-rotted manure, shredded leaves, lawn clippings or water-permeable fabric mulch will prevent water loss. If high winds are a problem, a windbreak can be a good idea: drying winds can cause moisture loss. Frequent weeding also reduces competition for water.

How much water to apply

Light sandy soils need watering more frequently than heavy soils, but less water can be applied at each watering. Heavier, clay-based soils can be watered less frequently, but need heavier applications of water because they hold more water within their structure.

A clay soil in which plants are wilting might need 81 litres per sq metre (17.5 gallons per 10 sq ft) and a sandy soil in which plants are wilting might need 60 litres per sq metre (12.2 gallons per 10 sq ft).

In practice, gardeners are unlikely to regularly let the soil get so dry that plants are wilting, so less water is required. Water can also be saved by applying it to the base of the plant rather than over a wide area. As a general guide, up to 24 litres per sq metre (5.2 gallons per 10 sq ft) every seven to 10 days will be sufficient to maintain plant growth.

Understanding the principles of effective watering can end the guesswork of when and how much to water, increasing yields and saving time, money and the environment in the process.