Why established shrubs still struggle in a dry spell

It is tempting to assume that a shrub which has been in the ground for five or ten years can fend for itself. In a typical British summer, it usually can. But when the rain stops for three or four weeks and the thermometer climbs past 25°C, even mature plants begin to feel the strain as the soil dries from the surface downwards.

The problem is rarely a lack of roots. It is that most of us water in a way that never reaches them. A quick sprinkle with the hose wets the top centimetre or two, evaporates within the hour, and encourages roots to creep upwards in search of moisture — exactly the opposite of what we want. Deep, infrequent watering builds a plant that can ride out a hosepipe ban; little and often builds one that cannot.

Water deeply, once a week

For most established shrubs in British gardens, a thorough soak once a week beats a light sprinkle every evening. Aim for roughly ten to twenty litres per plant per week in dry weather, poured slowly so it soaks in rather than running off. On light, sandy or chalky soils, where water drains away fast, lean towards the higher figure. On heavy clay, which holds moisture well, ten litres is often plenty.

Timing matters as much as volume. Water in the early morning or, better still, in the cool of the evening, when evaporation is at its lowest. Tip the can gently around the base rather than blasting the foliage, and a soaker hose left running along a border for an hour is one of the kindest ways to water a group of shrubs.

Target the root zone, not the trunk

• Water the drip line. A shrub's feeding roots spread outwards, often as far as the widest branches and beyond. Watering only at the trunk misses most of them.
• Make a shallow basin. Mound a ring of soil around the plant, roughly 60–90cm out from the stem, so water pools and sinks instead of running across the surface.
• Check the depth. Push a trowel or cane into the soil a few hours after watering. If it is damp 10cm down, you have done enough; if it is dry, carry on.
• Mulch generously. A 5–8cm layer of bark, garden compost or leaf mould slows evaporation dramatically, keeps the soil cooler and suppresses weeds. Keep it clear of the stem itself to avoid rotting.

Read your soil and your plants

Not every shrub is equally thirsty. Hydrangeas, rhododendrons, camellias, Japanese maples and moisture-loving viburnums will sulk quickly, letting you know with drooping leaves and scorched edges. Lavender, rosemary, cistus, hebe, berberis and cotoneaster are far tougher and actively resent too much water — give them a good soak once a fortnight at most.

Learn the difference between ordinary midday wilt, when leaves droop in the heat and recover by evening, and genuine drought stress, when a plant is still limp at dusk or its leaves curl inwards, yellow or turn crisp at the edges. A shrub in the rain shadow of a wall, beneath a mature tree, or in a container will always need attention first.

The wildlife dividend

Healthy, well-watered shrubs are the backbone of a wildlife-friendly garden: berries for blackbirds and thrushes in autumn, nectar for bees and hoverflies in spring, dense cover for nesting birds and hedgehogs. A drought-stressed shrub drops its flowers and fruit early, so watering well is about far more than keeping foliage green.

While the can is out, top up a shallow dish of water at ground level for hedgehogs and frogs, and keep a bird bath clean and filled. A few pebbles in a saucer give bees somewhere safe to land. All of this uses a fraction of the water a thirsty lawn would demand — and a lawn will green up again once the rain returns.

Building resilience for years to come

The best time to drought-proof a shrub is long before the drought arrives. Fork plenty of garden compost or well-rotted manure into the soil around the root zone each spring and the structure will hold water like a sponge. Autumn is the ideal season to plant new shrubs, giving roots months of cool, moist soil before their first summer.

Collect what rain you can. A water butt on a downpipe pays for itself in a single dry July, and rainwater suits plants better than tap water. Cooled water from cooking vegetables, or clean bathwater, can be used on ornamental shrubs — but keep it away from anything you plan to eat.

Finally, think about where you sit. A bench tucked among border shrubs, shaded by a mature viburnum or a scented philadelphus, becomes a genuinely lovely retreat on a warm evening. Watering by hand is slow work, but it is also the perfect excuse to be out at dusk, listening to the bees settle and watching the garden breathe again.