Is it bad to water plants in the middle of the day?

This question is really two questions wearing one coat. One is about damage, and the answer is that there is none. The other is about efficiency, and there the timing genuinely does matter — though far less than whether you are watering deeply or just wetting the surface.

Step by step

1. Settle the scorching myth.For a droplet to burn a leaf it would have to act as a lens focusing sunlight onto the leaf surface below it, and the geometry does not work — the focal point falls below the leaf. Hairy-leaved plants that hold droplets clear of the surface are a theoretical exception that has never been shown to matter in a garden.
2. Water a wilting plant when you find it.A plant flat at noon is losing water faster than its roots can supply. Waiting until evening on the strength of a myth costs it several more hours of damage.
3. Water early in the morning by preference.Least evaporation, the plant has water available before the heat of the day, and the foliage dries before nightfall, which reduces both fungal disease and slug activity.
4. Use the evening as the second choice.Evaporation is low, but foliage and soil surface stay wet overnight, which favours mildew, botrytis and slugs. On a dry sunny site it matters little; in a damp shaded garden it matters more.
5. Avoid overhead watering in the middle of a hot day.A sprinkler at noon can lose a substantial part of its output to evaporation before it reaches the ground. Watering at the base of plants at midday is much less wasteful than spraying over them.
6. Water deeply and less often.This matters more than any timing question. A long slow soak wets the soil to 200mm and more and pulls roots downward. A light daily sprinkle wets the top 20mm, keeps roots at the surface and leaves the plant helpless in the first dry week.
7. Check before you water.A finger pushed into the soil to the second knuckle tells you more than the appearance of the surface. Damp at 50mm means leave it alone.
8. Water the soil, not the leaves.The roots take up the water. Wetting the leaves achieves nothing except spreading fungal disease and losing water to evaporation.
9. Know when wilting is not thirst.Many plants — squash, hydrangeas, ligularia — wilt at midday in full sun and recover by evening even in damp soil, because the leaves cannot move water fast enough. If the soil is damp at 50mm and it recovers overnight, that is normal and it does not need watering.
10. Mulch, and do it after watering or after rain.Mulch cuts evaporation more than any change in timing. Applied to dry soil it seals the dryness in, so water first.

Tips

• The myth costs plants real damage every summer, because people leave wilting plants unwatered until evening.
• Depth beats timing. A weekly soak at any hour beats a daily sprinkle at the perfect hour.
• Established plants in the ground rarely need watering at all in a normal British summer. Containers, new plantings and crops are where the water should go.

Common mistakes

• Leaving a wilting plant until the evening — It is losing water and damaging tissue in the meantime, for no benefit at all. Water it.
• Running a sprinkler at midday — Much of it evaporates before it reaches the soil, and the rest wets foliage. If you must water in the day, water at the base.
• Light daily watering — It trains roots to sit in the top 20mm, where the soil dries first, so the plant becomes more vulnerable rather than less.
• Watering established shrubs and lawns in a normal summer — They have root systems reaching moisture you cannot see. Brown grass is dormant, not dead, and recovers with rain.

Questions people ask