The 2026/27 Chilterns Heatwave Guide: Keeping Your Hillside Garden Lush During a Dry Spell

Why Heatwaves Are the New Normal

The Chilterns is one of the driest parts of the UK, and heatwaves are becoming more frequent and more intense. The Met Office records show that the South East experienced heatwaves (5 or more days above 30 degrees Celsius) in 2022, 2023, 2025 and 2026. The 2026 heatwave saw temperatures reach 38 degrees Celsius in Marlow and High Wycombe, the highest ever recorded in the region.

Climate models predict that by 2030, the Chilterns will experience 5 to 8 heatwave events per year, compared to 1 to 2 in the 1990s. Annual rainfall is projected to decrease by 10 to 15 percent, with most of the decrease in summer. Gardeners in Oxfordshire, Buckinghamshire, Berkshire and Bedfordshire need to adapt.

This guide explains how to care for your garden during a heatwave, and how to make your garden more resilient to future heatwaves.

How Heat Affects Gardens

Heat affects gardens in several ways:

• Water loss: plants lose water through their leaves faster than roots can absorb it.
• Soil drying: chalky Chiltern soils dry out fast, sometimes within 2 to 3 days of watering.
• Lawn dormancy: grass goes brown and dormant to survive. Most lawns recover when rain returns.
• Container stress: pots dry out faster than the ground and may need watering twice a day.
• Fruit and vegetable drop: plants drop flowers or fruit to conserve water.
• Pest outbreaks: red spider mite and other pests thrive in hot, dry conditions.

How to Care for Your Garden During a Heatwave

Watering

• Water in the early morning (5 to 8 am) or evening (after 7 pm) to reduce evaporation.
• Water deeply once a week rather than lightly every day. Deep watering encourages deep roots.
• Prioritise: containers, new plantings, vegetables, and tender plants first. Established shrubs and trees usually survive without watering.
• Use a watering can for containers. Hosepipes waste water.
• Use grey water (bath and washing-up water) for established ornamental plants. Do not use on edibles.
• Check soil moisture by pushing a finger 5cm into the soil. If it feels dry, water.

Mulching

Mulch is the single best defence against heat. A 5cm layer of bark or compost reduces evaporation by 70 percent and keeps soil temperatures 5 to 10 degrees cooler. Apply mulch in spring before the heat arrives, and top up as needed.

Lawn Care in Heatwaves

• Do not mow during a heatwave. Cutting stresses the grass.
• Set the mower high (40 to 50mm) before the heatwave to shade the soil.
• Leave clippings on the lawn to act as mulch.
• If the lawn goes brown, accept it. Grass goes dormant and recovers when rain returns.
• Water only if you can commit to weekly. Sporadic watering does more harm than good.

Container Care

• Move containers to shade during the hottest part of the day.
• Group containers together to reduce evaporation.
• Use water-retaining gel in the compost.
• Stand containers in saucers of water during extreme heat.
• Water twice a day in extreme heat (35 degrees plus).

Protecting Tender Plants

• Move tender plants in pots to a shady spot.
• Use shade netting (40 percent shade) over tender plants in the ground.
• Water in the evening so plants have all night to absorb water.
• Mist foliage in the early morning to cool the plant.

How to Make Your Garden Heat-Resistant

Long-term, the best defence against heatwaves is to make your garden more resilient. This means:

1. Choose Drought-Tolerant Plants

Replace thirsty plants (hydrangeas, hostas, rodgersias) with drought-tolerant ones. See our drought-tolerant plant guide. The best choices for Chiltern gardens:

• Lavender, silver foliage reflects sun
• Rosemary, evergreen, drought-tolerant
• Verbena bonariensis, tall, airy, deep roots
• Sedum, fleshy leaves store water
• Eryngium, spiky blue flowers, deep roots

2. Improve the Soil

Add organic matter annually to improve water retention. On chalky soils, this is essential. Mulch thickly every spring.

3. Install Irrigation

A drip irrigation system with a timer is the most efficient way to water. It uses 50 percent less water than a hosepipe and delivers water to the roots where it is needed.

4. Reduce Lawn Area

Lawns are the thirstiest part of the garden. Consider replacing some lawn with gravel, ground cover, or wildflower meadow. See our guide to gravel and permeable surfaces.

5. Plant Trees for Shade

Trees provide shade and cool the air through transpiration. A mature tree can cool the air by 2 to 4 degrees. Choose drought-tolerant trees like oak, beech, and rowan.

The Heatwave Action Plan

When a heatwave is forecast:

1. Water deeply the day before the heatwave arrives.
2. Move containers to shade.
3. Apply shade netting to tender plants.
4. Do not mow the lawn.
5. Check containers twice a day during extreme heat.
6. Mist foliage in the early morning.
7. Harvest ripe fruit and vegetables to reduce plant stress.

Common Mistakes

• Watering at midday. Most water evaporates. Water in the morning or evening.
• Watering lightly every day. This encourages shallow roots. Water deeply once a week.
• Mowing during a heatwave. Cutting stresses the grass. Wait until the heat breaks.
• Not mulching. Bare soil bakes hard and loses moisture. Mulch is essential.
• Planting thirsty plants on chalk. Hydrangeas and hostas will struggle. Choose drought-tolerant plants instead.

Frequently Asked Questions

Will my lawn recover from going brown?

Yes, in most cases. Grass goes dormant in drought and recovers when rain returns. If the drought lasts more than 8 weeks, some grass may die and need overseeding in autumn.

How often should I water during a heatwave?

Containers: daily, twice a day in extreme heat. New plantings: every 2 to 3 days. Established plants: weekly. Lawns: only if you can commit to weekly, otherwise let them go dormant.

Should I use a hosepipe during a heatwave?

Only if there is no hosepipe ban. Check with your water company. Even without a ban, use a watering can for containers to save water.

Get Help Preparing Your Garden for Heat

If your garden in Oxfordshire, Buckinghamshire, Berkshire or Bedfordshire is struggling in the heat, send us a WhatsApp with photos and we will aim to respond within 12 to 36 hours, Monday to Sunday.

Further Reading

• Best drought-tolerant plants
• Gravel and permeable surfaces
• Keep your lawn green in dry summers

Sources and citations

This article draws on the following sources. Specific claims are cited inline where relevant.

1. CGM field records (2025-09. Site observations from gardens across Oxfordshire, Buckinghamshire, Berkshire and Bedfordshire.
2. Royal Horticultural Society (2024). RHS Gardening Advice and Plant Finder. Available at rhs.org.uk.
3. Met Office (2024). Regional climate averages, South East England. Available at metoffice.gov.uk.
4. British Geological Survey (2024). Soil parent material data for the Chilterns and Thames Valley. Available at bgs.ac.uk.