Why New Trees Need Help Through a British Summer

A tree that has just gone into the ground is, in many ways, still in a state of shock. Whether it arrived bare-root in winter or as a container-grown specimen, it has lost most of the fine, hair-like roots that once drew water from the nursery soil. Until it grows new ones, it survives on the moisture in the rootball and whatever you provide. That establishment phase lasts two, sometimes three full growing seasons.

British summers are unpredictable. We can go from a soggy June to six weeks of hard, baking sun with barely a drop. A steady drizzle that keeps the lawn green will not soak down to the roots of a young tree — often only the top centimetre or two of soil gets wet, while the rootball underneath stays bone dry. This is why a stint of light showers can be followed by a tree that suddenly wilts in August.

The good news is that new trees are not difficult to look after. They need one thing done properly and one thing done consistently: a deep soak, and a mulch to hold on to it.

How Much, and How Often

Forget the little-and-often approach. A quick splash every evening encourages roots to stay near the surface, where the soil dries fastest. Far better to give the tree a proper drink less frequently, so water travels down and the roots follow it.

As a working guide for a newly planted tree, aim for around 10 to 20 litres at a time in normal summer weather, and up to 30 litres or more in a genuinely dry spell. A large specimen, or one planted on light sandy soil, will want the upper end of that range. Frequency matters as much as volume: once thoroughly soaked, most soils will hold enough for three or four days, so twice a week is usually plenty. On heavy clay the water lingers longer; on chalk or sandy ground it disappears quickly.

• Check before you water. Push a trowel or your fingers 10cm into the soil beside the rootball. If it feels damp at that depth, leave it alone.
• Water the rootball, not the trunk. Aim for the base of the tree and outwards to the edge of the canopy — that is where the roots will spread.
• Water in stages. Tip on half the water, wait for it to sink in, then add the rest. This avoids run-off on sloping or compacted ground.
• Trees in pots need more. A container-grown tree in summer may need water daily, and the compost should never be allowed to dry out completely.

Watering Slowly Makes All the Difference

The single biggest mistake in summer watering is speed. A hosepipe on full bore across a rootball simply bounces off the surface and runs away across the lawn. What you want is a slow trickle that has time to soak in.

A watering can fitted with a rose is ideal for smaller trees. For larger ones, lay a hose on the ground at a gentle trickle and move it around every twenty minutes or so. A punctured bucket or a length of leaky pipe set beside the trunk works beautifully — you fill it once and let gravity do the work. If you are watering several trees, a simple soaker hose laid in a loop around each one is worth the outlay.

Early morning or evening is best, simply because less is lost to evaporation. A gravel or grit top-dressing around the base, or even a temporary ridge of soil, can help direct water to where it is needed rather than letting it run away.

Mulch: The Quiet Hero of Summer Tree Care

If you do only one extra job this summer, make it mulching. A generous layer of organic material over the root area reduces evaporation from the soil surface, keeps the ground cooler, suppresses weeds and slowly feeds the soil as it breaks down.

Well-rotted bark, garden compost, leafmould or spent mushroom compost are all suitable. Spread it 5 to 8cm deep over a circle at least a metre across — wider for bigger trees.

• Keep it clear of the trunk. Leave a gap of around 10cm so bark stays dry and air can circulate. Piling mulch against the stem invites rot and can attract rodents.
• Water first, then mulch. Mulch holds moisture in; it does not create it. Soaking dry soil beneath a fresh layer of bark is a wasted effort.
• Top it up, don't dig it in. Lightly fork over old mulch to keep it open, but avoid cultivating around shallow new roots.

Keep the Competition Down

Grass and weeds are thirsty, and they will happily take water and nutrients from a young tree's root zone. A tree planted in the middle of a lawn will always struggle more than one with a clear circle around it.

Maintain a weed-free area at least 60cm across, ideally a metre, for the first two or three summers. Hand-weed or hoe lightly, taking care not to damage surface roots. Mulch does most of this work for you, but check occasionally for couch grass and bindweed creeping in from the edges.

Reading the Signs, and When to Stop

Drought stress shows up in predictable ways: leaves that droop or curl, scorched brown edges, a dull greyish-green colour, and in severe cases early leaf fall in August. Small leaves and short extension growth the following spring are a sign the tree went short of water the summer before.

Overwatering causes its own trouble, particularly on clay. Yellowing leaves, soggy ground that never dries, and a sour smell around the base all point to waterlogged roots rather than thirst. If your soil stays wet, cut back and let it drain.

Finally, don't down tools in September. A dry autumn is hard on newly planted trees, and they benefit from watering right through until leaf fall, well into October in most years. Established trees in a normal summer need no help at all — but if a prolonged drought arrives, a good soak once a fortnight will see even older specimens through in better shape.