How to revive your garden in a long hot summer

After July’s record-breaking heatwave and weeks without significant rain in many areas, gardens have turned brown as the grass closes down and trees show signs of stress – and now hosepipe bans are about to begin in some regions. Plants are well adapted to survive drought with very little or no watering. However, with climate change, droughts are likely to be more frequent and prolonged. Although gardeners can cope now by carefully targeted watering, this is unlikely to remain true in future.

Each winter, including last winter, rains restock the soil with water to at least the depth of plant roots (most of which are in the top metre of soil). Usually they go much deeper than that. This raises the water table, bringing springs to life and filling rivers. However, in many regions, little significant rain has fallen since April, leading to lower than usual soil moisture levels.

In some areas, south London for example, only 36 per cent of long-term average June rainfall fell this year, compared to parts of Somerset where 137 per cent of long-term rain fell. Although there was also little rainfall in the famous drought year of 1976, average consumption per person has increased since then. With a bigger population, “water stress” is reached at lower rainfall thresholds – and this inevitably leads to restrictions, including hosepipe bans.

Let’s hope that the autumn rains and cool, dewy nights soon arrive to restore our gardens.

Lawns

Lawns, even fine ones, should be allowed to brown during a drought. They will almost always “green up” after rain. Although some bald patches occasionally result, these can be repaired in late September and will be good by spring. Gardeners should avoid or severely limit lawn sprinklers.  

Meadows tolerate drought better than a traditional lawn as they comprise many deep-rooted plants that remain green when grasses go brown. Converting some or even all of a lawn to a meadowlike format reduces the need to water.  

Specially bred drought-tolerant grass mixes, water-saving micro-leaved clovers and novel no-mow groundcover plants such as Kurapia potentially work better in dry regions, particularly where the soil is sandy.

So-called “alternative lawns”, made from sedum, thyme and other drought-resistant plants, need a lot of work to look good and don’t tolerate much trampling. Non-grass “lawns”, made with low-spreading plants such as creeping Jenny, white clover and self-heal, are more robust, while needing no water. Heat- and drought-resistant grasses, Bermuda grass for example, used in Florida and Spain, are unreliable in our winters.

Trees and shrubs

Trees, shrubs, roses, fruit and climbers have deeper roots than grasses but, by late summer without rain – particularly where the soil is thin or sandy, as at RHS Garden Wisley – they shed leaves and begin to show signs of autumn colours. Not because autumn is early, but as a mechanism to save water and avoid lethal damage. Woody plants on deeper or more clay-rich soils show less stress.

It is vital to water young trees and shrubs which have yet to develop extensive roots. Watering bags (water-filled pouches that wrap around trunks), are economical and release a steady drip of water. Alternatively, make a saucer-like depression in the soil around the base of the trunk and fill this once a week to deeply soak the soil. Remove weeds and vegetation from around young trees to reduce competition for water. Don’t trickle a hose overnight – this is deeply wasteful and might even drown roots which, in warm soils, are very sensitive to lack of oxygen.

Beds and borders

Cut back spring- and early summer-flowering plants, such as dicentra, delphiniums, geraniums, irises and lupins now. They will leaf out and perhaps flower again after September rains.

Summer-flowering plants, such as helenium, helianthus, monarda and phlox, usually enjoy hot, dry conditions and seldom need watering, even if they wilt at midday. Once they’ve flowered, deadheading and cutting back will limit their water needs.

Dahlias, fuchsias and other classic long-flowering summer border plants may need watering. Longterm, improve the soil before and after planting by incorporating compost or manure and using organic mulches to reduce watering. In dry areas, plant them where they get a little shade in midsummer.

Pots and baskets

RHS research has shown that gardeners frequently overwater containers. Just to give an idea, a standard hanging basket only needs a daily mugful of water per plant.

Here are some basic water-saving dodges: stand pots in saucers or trays to collect water so it can be reabsorbed; group pots so they form a humid area that limits evaporation; move them into a shadier spot; use self-watering container (that contain a reservoir).

Fruit and vegetables

Being mostly made of water, fruit and vegetables benefit from regular watering but even here savings can be made. Target watering at crucial growth stages. For example, plants that form hearts, like lettuces and cauliflowers, need more watering when the initial rosette forms – this will carry them through to harvest. Plants that produce pods or fruits, e.g. peas and sweetcorn, need more water when they flower. Exceptions are runner beans, which soon stop producing if they run dry, and tomatoes, which develop disorders if under-watered.

Ponds and water features

Topping up ponds might be necessary for fish welfare but muddy or even dried-up ponds can still support wildlife and can often be left for replenishment by later rains. Water features might be needed to oxygenate water for fish, but otherwise switch them off – moving water evaporates more quickly than still.