The Royal Horticultural Society (RHS) advises watering plants deeply but less often during heatwaves, with early morning as the optimal time. This approach reduces evaporation, strengthens roots, and helps plants withstand heat stress.
Why Early Morning Watering Is Best
According to the RHS, early morning watering allows water to soak into the soil before the sun intensifies, minimising evaporation. Plants then have moisture reserves to cope with the hottest part of the day. Additionally, leaves dry out before nightfall, reducing fungal disease risks.
The next best option is late afternoon or dusk, when temperatures drop. However, experts recommend watering at the base of plants to avoid wet leaves overnight, especially in humid conditions.
Avoid Midday and Shallow Watering
Watering during the middle of the day is least effective, as high temperatures cause significant water loss through evaporation before it reaches roots. The RHS also warns against watering little and often, which encourages shallow root growth near the surface where soil dries fastest. Instead, deep, infrequent watering forces roots to grow deeper, making plants more resilient.
Use the Finger Test
To determine if plants need water, insert a finger a few centimetres into the soil. If moist, delay watering; if dry, it is time to water again. This simple test prevents overwatering and promotes efficient water use.
Prioritise Containers and New Plants
Pots, planters, and hanging baskets suffer more during heatwaves due to limited soil volume. They may need more frequent watering, but always check soil moisture first. Grouping pots in partial shade during peak heat reduces moisture loss. The RHS advises prioritising newly planted specimens, vegetables, and containers over established trees, shrubs, and perennials, which often need no regular watering even in warm weather.
Mulch to Retain Moisture
Applying a layer of mulch—such as pine bark, dry leaves, or compost—around plants acts as a natural insulator, reducing evaporation and protecting roots from heat. This simple measure helps maintain soil moisture for longer.
Heatwave Watering Checklist
- Water early in the morning where possible
- Water at the base of the plant, not the leaves
- Water deeply rather than little and often
- Check soil moisture before watering again
- Mulch exposed soil to reduce evaporation
- Give extra attention to pots and hanging baskets
- Avoid watering during the hottest part of the day
