Why young trees need you in a dry summer

A newly planted tree is a strange thing: a big, hopeful top growth sitting on a surprisingly small ball of roots. When it was lifted from the nursery, most of its fine, water-gathering roots were left behind in the field. What you planted in your garden is essentially a tree living out of a bucket of soil for its first few seasons, and that bucket dries out fast when the rain stops.

British summers are unreliable in the most awkward way. We can have a fortnight of soft drizzle, then three weeks of hard sun and a drying wind, and it is those dry spells that undo a spring planting. An established oak or beech will send roots metres down and shrug it off. Your two-year-old field maple cannot. Until it has stretched its roots out into the surrounding soil — usually by the end of its third summer — watering is the single most useful thing you can do for it.

One thorough soak a week, not a daily sprinkle

The commonest mistake is little and often. A quick splash every evening feels kind, but it only wets the top centimetre or two, which then evaporates in the sun. Worse, it encourages roots to stay shallow, right where the soil dries out fastest.

Aim instead for one generous soak roughly every seven days in dry weather. As a working guide:

• 10 to 15 litres per week for a young tree in its first summer on loamy soil.
• 20 litres or more on sandy or chalky ground, which drains away beneath you.
• Double it for anything still in a pot, and for trees planted into heavy competition from grass or hedges.

If the week is cool and showery, skip it. If it is hot, breezy and the soil is cracking, give the full amount. Judging by the calendar alone will let you down; judging by the soil will not.

Aim for the roots, not the leaves

Water landing on foliage is largely wasted — it evaporates before it reaches the ground, and in strong sun it can scorch. The root zone you want to reach is the soil directly above and just beyond the original root ball: roughly a circle the width of the branch spread. Keep water off the trunk itself, where constant damp can soften the bark.

Pouring slowly is what makes the difference. A full can emptied in five seconds mostly runs off across the surface; the same can trickled out over five minutes sinks in properly. Practical ways to slow it down:

• Run a hosepipe on the merest dribble and move it around the tree in stages, twenty minutes or so in total.
• Form a shallow ring of soil, or a low earth basin, around the tree so water pools and soaks downwards instead of running away.
• Sink a length of pipe or a bottomless plastic bottle beside the trunk and fill it — the water is delivered below the surface, right where roots are working.

Then check your work. Push a finger or a trowel 10cm into the soil an hour later. Damp at that depth means you have done the job; dry means you have only watered the surface.

Mulch: the quiet hero of summer watering

A generous mulch does half the watering for you. Spread 5 to 8cm of well-rotted compost, leafmould or bark chip over the root zone in late spring, before the ground dries. It keeps the soil cool, slows evaporation, and smothers the weeds and grass that would otherwise be drinking your tree's water.

Leave a clear gap of a few centimetres around the trunk — mulch piled against bark holds moisture where you do not want it and can encourage rot. Top the mulch up mid-summer if it has thinned, and water underneath it rather than onto it.

Timing, stress signals and going away

Water in the early morning or, better still, in the evening, when less is lost to the air. Midday watering in a heatwave is mostly a gift to the atmosphere.

Learn to read the tree. Fine leaves curling, a dull grey-green look, scorched brown edges, small leaves or early autumn colour in August are all signs of drought stress. Flagging foliage that perks up overnight is usually fine; foliage that stays limp by the following morning needs water at once.

If you are away, a neighbour with a watering can and clear instructions is worth more than any gadget. During a hosepipe ban, a watering can is normally still allowed for young trees, but check your water supplier's rules before you assume. Water butts, bath water and cooled washing-up water are all fine for ornamentals — avoid anything heavily bleached or soapy, and keep grey water off edibles.

Choosing and aftercare for woodland planting

If you are planting a small copse or a wildlife corner, choose natives that will eventually look after themselves: field maple, hornbeam, rowan, wild cherry, crab apple, hawthorn, hazel, birch, lime and oak. They are adapted to British conditions and, once settled, tolerate our dry spells well.

Keep watering through the first three summers, easing off in late August so growth hardens before winter. By the time the trunk is a good 4 or 5cm across, your tree has found its own water and you can put the can away. Those first few seasons of steady, patient soaking are what buy you a lifetime of shade.