Tips on when to water your thirsty plants

Hos often to do it, and what time of day is best? Olive Ryan has the answers
Tips on when to water your thirsty plants

CAN DO: Watering sunflowers

WHEN the warmer weather graces our shores, our gardens and outdoor spaces can become a perfect oasis for rest and relaxation.

But as nice as the hot weather might be, extreme conditions and high temperatures can wreak havoc on your plants.

A lot of fuss is made about watering in the morning compared to watering in the evening. Drive around your locality on a hot summer day, and you’ll see many approaches to watering plants, from drip irrigation to sprinkler systems to watering cans.

Timing your irrigation will not only lead to healthier plants, but it can also save on your water bill and conserve water. But the big question is what time is best?

The answer is, it all depends on circumstances.

In general, it is best to administer water from an overhead device like a sprinkler or rain wand in the morning — watering plants in the early morning, while it is still cool, will allow the water to run down into the soil and reach the roots of the plant without too much excess water being lost to evaporation.

Watering in the early morning will also make the water available to the plants throughout the day, so that they will be able to deal better with the heat of the sun.

There is a gardening myth that watering in the morning will make the plants susceptible to scorch. Almost all areas in the world, especially ours, do not get intense enough sun for water droplets to scorch the plants.

Even if you live in an area where the sun is intense, the water droplets would have evaporated in the heat long before the sun could reach those damaging temperatures.

Sometimes, due to work and life schedules, it can be difficult to water the garden in the early morning. The second-best time to water a garden is in the late afternoon or early evening.

If you are watering in late afternoon, the heat of the day should have mostly passed, but there should still be enough sun left to dry the plants a bit before night falls.

Watering plants in the late afternoon or early evening also cuts down on evaporation and allows the plants several hours without sun to take up water into their system.

One thing to be careful of if you water in the late afternoon is to make sure that the leaves have a little time to dry before night comes. This is because damp leaves at night encourage fungal problems, such as powdery mildew or sooty mould, which can harm your precious plants.

On the other hand, evening watering gives plenty of time for the water to penetrate the soil and for the plant to take it up, but there is a concern that, by allowing the leaves to remain damp overnight, it will provide an ideal habitat for disease pathogens to penetrate your plants.

If you are using a drip or soaker irrigation system, you can water right up until nightfall, as the leaves of the plant do not get wet with this form of watering.

All living things need water to allow chemical reactions in their cells that provide energy for growth.

Plants also need water to carry nutrients from the soil to the growing cells. This water is drawn up to replace water lost through stomata — the breathing holes in leaves. These stomata are needed for gas exchange — carbon dioxide in, oxygen out — during photosynthesis.

In high light levels, on sunny days, a lot of carbon dioxide is fixed to make sugars by photosynthesis.

Loss of water is also important to cool plants on hot days.

If plants run short of water, they shut down their stomata and photosynthesis stops and is replaced by photorespiration — a process that releases carbon dioxide. Desert plants get around this by breathing at night and storing carbon dioxide for release to photosynthesis during the day while the stomata are shut. But in our gardens, few plants are adapted to do that

Knowing whether your plants are annuals or perennials is a key factor in deciding when to water plants during a hot spell.

Annuals are plants that finish their entire life cycle in one growing season. These have very shallow root systems and will suffer when the top few inches of soil dry out in the summer. You must water them frequently, even daily, when the temperature rises.

Perennial plants have deeper root systems that enable them to survive periods of drought from one season to the next.

Some perennials have taproots that extend many inches into the soil, in effect tapping into water reserves during periods without rainfall.

The best time to water perennial plants is once or twice a week, slowly and deeply so that the water does not run off before it has time to soak into the soil, as many plants thrive on about an inch of water per week.

Seeing your favourite plants drooping on a hot day can feel like an alarm bell going off in your head. Wilting can make plants look like they are on death’s door, and in some cases, they may be.

However, other things can cause wilting, including pest and disease problems, and even overwatering.

Furthermore, plants can wilt on a hot day as a way to cope with temperature, but then rebound when the evening cools off.

You can re-check your plants late in the evening and determine if the wilting was due to temporary heat stress before watering. In time, you will get to know your plants and will recognise those that respond to high temperatures in this fashion.

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