Watering in a Heatwave: When, How Much, How to Save Water
Heatwave watering in one sentence: rarely, generously, at the base, early in the morning. Water less often but deeply (in open ground, in the order of 10 to 20 L/m² per session, every 2-3 days) rather than a daily trickle that evaporates and weakens the roots. This guide details the timing, the quantities and the mistakes to avoid; for the full picture, see the garden and heatwave guide.
The Chatelain Method for watering
We observe the real moisture of the soil (with a finger, at 5 cm); we diagnose the true need; we correct with deep, targeted watering; we prevent waste with mulch and rainwater.
When to water: morning or evening?
Both work, but the morning wins by a nose. Here are the trade-offs.
| Time | Advantages | Worth knowing |
|---|---|---|
| Early morning (before 8 am) | Plant hydrated for the day, foliage dries off | The best compromise in a heatwave |
| Late evening (after 8 pm) | Low evaporation, soil soaks in overnight | Wet foliage at night: slugs, diseases |
| In the middle of the day | — | To be avoided: maximum evaporation, wasted water |
The Chatelain’s rule of thumb. The fear of droplets « burning » leaves by acting as magnifying glasses is, for most plants, a myth. The real reason not to water at noon is evaporation: under a heatwave sun, a large share of the water evaporates before reaching the roots. We water in the cool hours out of thrift, not superstition.
How much water: less often, more thoroughly
The most widespread mistake is shallow daily watering: it only wets the first few centimetres and encourages the roots to stay at the surface, where the heat strikes. Better a deep, spaced watering that invites the roots to dive.
| Type | Quantity benchmark | Frequency in a heatwave |
|---|---|---|
| Border / vegetable bed in open ground | 10 to 20 L/m² | every 2-3 days |
| Young tree/shrub | several dozen litres | once a week, deeply |
| Pot / planter | until it drains | 1 to 2 times a day depending on volume |
Adjust these benchmarks to the soil (sandy = more often, clay = more spaced out), the wind and the exposure.
How to water: the technique that saves water
- At the base, never on the foliage: aim for the roots, avoid evaporation and disease.
- Slowly: water poured too fast runs off without soaking in. Give the soil time to absorb.
- Hoe before watering: breaking the surface crust helps the water go down — « one hoeing is worth two waterings », as the saying goes.
- Mulch systematically: 7 to 10 cm sharply cuts water needs (see the best mulch to retain moisture).
- Favour rainwater: free, lime-free and exempt from restrictions (see harvesting rainwater in the garden).
To aim true without waste, tools that deliver water straight to the roots are precious: see terracotta ollas in the vegetable garden, and automatic watering for time away. For the vegetable garden specifically, see protecting the vegetable garden from a heatwave; in the orchard, watering fruit trees.
The 5 heatwave watering mistakes
- The shallow daily trickle: surface roots, weakened plants.
- Watering in the middle of the day: half the water evaporates.
- Sprinkling the foliage: evaporation and disease, little water to the roots.
- Skipping the mulch: on bare soil, the watering evaporates at once.
- Watering without checking the soil: you sometimes drown a plant that wasn’t thirsty.
🛒 What I need
As an Amazon Associate, we earn from qualifying purchases — sponsored links, at no extra cost to you.
Triggers the watering early in the morning, automatically, in the cool hours.
For slow, deep watering at the base, without waste.
Delivers in one go the deep volume the plant needs.
Keeps the soil cool and cuts water needs.
FAQ
Is it better to water in the morning or the evening in a heatwave?
Morning is slightly better: the plant benefits from the water all day and the foliage dries, which limits disease. Evening also works, but foliage that stays wet overnight favours slugs and fungi.
How many litres of water per square metre during a heatwave?
In open ground, count in the order of 10 to 20 litres per square metre per watering, every 2 to 3 days, rather than a small daily dose. Adjust to soil, wind and exposure.
Should you water every day in very hot weather?
No, except pots and planters. In open ground, a deep watering every 2-3 days beats a shallow daily one, which keeps fragile roots at the surface.
How can you save watering water in summer?
Mulch the soil, water at the base early in the morning, hoe to help the water soak in, use rainwater and targeted diffusers such as ollas or drip lines.
Sources and further reading
- Jardiland — how and when to water during a heatwave
- Jardiner Autrement — saving water in the garden
- Aujardin.info — summer watering
- Back to Garden Care and Permaculture
Written and verified by the editorial team at Les Jardins d’un Chatelain.