Why dry spells hit trees harder than you think

Trees are remarkably resilient, but a prolonged dry spell — especially one that follows a dry spring or a hot, windy summer — puts them under real strain. Unlike bedding plants that wilt dramatically and recover overnight, trees suffer quietly. Their roots draw moisture from a surprisingly wide area, and when the top layer of soil dries out, they cannot simply move elsewhere. In British gardens, our typical clay or sandy loams can bake hard on the surface whilst remaining dry well below. The result is slower growth, smaller leaves, early leaf drop, and a greater vulnerability to pests and diseases. For newly planted trees, the stakes are even higher. Their roots have not yet spread into the surrounding soil, so they rely almost entirely on the water you provide.

The golden rule: water slowly and deeply

Light sprinkling is worse than useless. It wets only the top centimetre or two of soil, encouraging shallow roots that are the first to suffer when the surface dries. Instead, water slowly and deeply so that moisture reaches 20–30 cm down, where the majority of a tree's feeding roots live. A gentle trickle from a hose left in place for an hour or two is ideal, or use a watering can with the rose removed to deliver water directly to the soil. For a newly planted tree, aim for 10–20 litres per week in dry weather, applied in one or two sessions. For an established tree, 50–100 litres per week may be needed, depending on size and soil. If you are on a hosepipe ban, a large watering can or a connected series of buckets works perfectly well.

Water the root zone, not the trunk

The most common mistake is to aim water at the base of the trunk. That does little for the tree and can even cause rot if the bark stays wet. Instead, water the root zone — the area under the canopy, extending out to the drip line (the outermost reach of the branches) and a little beyond. For young trees, this is a circle roughly 1–1.5 metres across. For mature trees, think in terms of a broad ring rather than a single spot. Move your hose or can around to moisten the whole area evenly. If the soil is very dry and baked, prick it over lightly with a fork first so water can soak in rather than running off. On slopes or heavy clay, water in stages, allowing each dose to sink in before adding more.

Mulch to lock in moisture

Once you have watered, a generous layer of mulch is your best ally. It shades the soil, slows evaporation, and keeps the root zone cooler. Use well-rotted manure, leaf mould, garden compost, or bark chips. Apply a layer 5–8 cm deep, but keep it clear of the trunk — a doughnut shape, not a volcano. Mulch piled against the bark can trap moisture and lead to decay. Water the ground thoroughly before mulching, not after, so the moisture is already where the roots need it. Top up the mulch each spring, and it will also suppress weeds that would otherwise compete for water.

When and how often to water

Timing matters as much as quantity. Early morning is best, when the soil is cool and evaporation is low. Evening is the next best option, though it can encourage slugs and fungal problems in some gardens. Avoid watering in the heat of the day — much of it will evaporate before it reaches the roots. As for frequency, check the soil before you water. Push a finger or a slim trowel 10 cm into the ground. If it feels dry, water. If it is damp, wait. During a prolonged dry spell, a deep watering once a week is usually far better than a daily sprinkle. For newly planted trees, check every few days. For established trees, every 7–10 days is often enough, but always be guided by the soil, not the calendar.

Helping trees recover and build resilience

After the dry spell breaks, do not assume the job is done. Trees can take weeks or even months to show the full effects of drought. Keep an eye out for signs of stress:

• Early autumn colour
• Sparse foliage
• Dieback in the crown
• Smaller than usual leaves

Continue to water if the autumn is dry, especially for young trees. Avoid feeding with a high-nitrogen fertiliser during drought — it encourages soft growth that demands more water. Instead, a light mulch and a deep soak now and then will help roots recover. Over time, a well-mulched, properly watered tree will develop a deeper, more extensive root system, making it better able to withstand the next dry spell. British weather is famously changeable, but when the rain does stop for weeks on end, a little thoughtful care goes a long way.