Should you water plants in full sun?

It's the last straw that breaks the camel's back!

Some old gardeners proclaim loudly: “If you water your plants in full sun, they might burn!” Indeed, there is a tendency to think that water droplets exposed to sunlight could act like a magnifying glass on the foliage of plants, causing burns similar to sunburns. But is this true?

A study was conducted in Hungary on this subject, and its results are quite surprising! It shows that smooth, hairless foliage is unlikely to suffer damage. In contrast, hairy foliage, such as that of a floating fern (Salvinia natans) in the experiment, can suffer sun damage due to this so-called “magnifying effect”. Indeed, because of its hairs, the water droplet does not make direct contact with the fern leaf, creating a small space conducive to the magnifying effect and thus resulting in a sunburn. However, the experiment was not conducted on all plant species, nor in different regions of the world, even though summers are very hot in Hungary (averaging between 27 to 30°C).

Therefore, it is better to refrain from watering foliage in full sun. Additionally, tap water, which is very hard, will leave unsightly white marks on the foliage.

It is worth noting that some plants, such as tomatoes, tend to develop fungal diseases if their foliage is watered. Yet another good reason to water directly at the base of the plants.

→ To learn more, find this study here

Tomatoes should be watered less frequently but thoroughly, using a watering can, and without wetting the foliage

Evaporation under the sun

In the middle of the day, your garden basks under the scorching rays of the sun, which also warm your soil. This ambient heat will accelerate the evaporation of water, and consequently, your watering will be much less effective than in the early morning or evening. In short: the hotter it is, the faster the water evaporates, the less it penetrates the soil down to the roots, and the less your plants will be properly quenched.

Certainly, you can water, but you will need to provide double the amount of water during the day, whereas a single watering can would have sufficed by nightfall. You will thus empty your water reserves more quickly or further increase your bill. Moreover, water is a precious resource these days, not to be overlooked!

Watering will be more effective in the evening or morning

Play hot and cold

In the height of summer, the thermometer can quickly soar under the sun. Plants also endure these high temperatures, and you may sometimes notice wilting and trailing foliage. If you decide to water your plant during the day, ensure that your water is at room temperature. Indeed, cold water straight from the tap can cause thermal stress at the root level, potentially weakening your perennials and other bushes further. To avoid this, leave your watering can in the sun for a few hours or wait until the evening when temperatures are cooler to water your garden.

Leave your watering can full at room temperature for a few hours before using it

In conclusion

The best time of day to water your garden is late in the evening or very early in the morning. However, if your plant’s survival is at stake or if you have time constraints, you can water during the day by taking a few precautions: water 2 to 3 times more generously, only at the base of the plants, and use water at room temperature.

For further reading

Discover Olivier’s tips for properly watering your plants in summer and maintaining soil moisture: