Start by Standing Back

Most of what you need to know about a tree's health is visible from ten or fifteen paces away, on a bright day, with your hands still in your pockets. The trick is to look at the whole tree before you look at any part of it. Walk round it, look up into the crown, and then look down at the base. A healthy tree has a certain balance to it — a full, well-shaped canopy, a clean trunk, a firm root flare where it meets the ground. When something breaks that pattern, it usually means something.

Late summer is the best time for a quick assessment. Foliage is at its fullest, any dieback stands out, and fungi have had a season to push up their brackets. Winter is useful too, but only if you know the tree — a bare oak looks alarming until you remember it is supposed to be.

The Silhouette: Deadwood and Crown Shape

Every tree drops some twigs and small branches; a scattering of deadwood in the middle of a mature oak is entirely normal and often valuable to insects and bats. What matters is how much, and where.

• Deadwood high in the crown, especially large limbs, is more serious than a few dead twigs lower down.
• Fine twigs snapping off in your hand — brittle, dry, with no green beneath the bark — suggest the branch has been dead for a while.
• A one-sided crown, where growth has failed on one side, can point to root damage, compaction or a wound on that side of the trunk.
• A stag-headed crown, with bare, antler-like limbs above a normal canopy, is natural in ancient oaks and sweet chestnuts but worrying in a young, vigorous tree.

Compare the tree with others of the same species nearby. Sycamore and ash are often the first to show thinning at the top, while beech tends to hold its shape until something is badly wrong.

Leaves: Density, Colour and Timing

Foliage is the tree's report card. From midsummer, a healthy crown should be dense enough that you cannot easily see the sky through it in the middle of the day. If you can count branches through the leaves in July, the tree is under stress.

Look for leaves that are smaller than they should be, pale or yellow between the veins, or turning early — rusty tints in August on a birch or a horse chestnut are not autumn arriving early, they are the tree shutting down sections of itself. Late leafing in spring, or a bare patch where leaves simply never appeared, is the same message from the other end of the year.

Evergreens need their own reading. A Scots pine should carry three or four years of needles; if the inner needles have gone and only the tips are green, the crown is thinning. Larch going bare in July rather than November is a clear warning. Some quirks are harmless: young beech and oak hold on to their dead brown leaves through winter, and horse chestnut blotches from leaf miner are disfiguring but rarely fatal.

Fungal Brackets and What They Tell You

Fruiting bodies are the most honest sign a tree gives you, because by the time you can see them, the fungus has usually been working inside the wood for years. Look at the base of the trunk, the root flare and any old wounds, and check both sides of the tree — the compression side, leaning downhill, is often the first to show.

• Soft, pale, annual brackets that crumble easily are usually working on dead wood, which is less alarming.
• Hard, dark, perennial brackets that return year after year are digesting heartwood, and that is a structural problem.
• Honey-coloured toadstools in clusters at the base, with black bootlace strands or a white fan of tissue under loose bark, point to honey fungus — the most destructive root disease in British gardens and hedgerows.
• A dense tuft of brackets on a trunk, well above ground, suggests the decay is already high up inside the tree.

Not every fungus is a killer. Many are recyclers doing useful work on wood that is already dead. But a bracket at the base of a tree you walk under every day deserves a proper look.

Bark, Wounds and the Root Flare

Run your eye up the trunk. Healthy bark on most species is continuous and firm. Watch for patches of dead, loose or sunken bark, vertical cracks that have opened suddenly, and old wounds that have not sealed with a roll of callus tissue around the edge. Shedding bark is normal on beech, sycamore and birch — the question is whether what lies beneath is sound and dry.

Hollowing is not a death sentence; many ancient trees are hollow and live for centuries. What matters is how much sound wood remains around the hollow, and whether the tree is leaning with a heaving root plate. Push a heel into the ground at the base: soft, lifted or cracked soil is a serious sign. Ivy hides all of this beautifully, so it is worth parting it to look.

When to Watch, When to Act

Keep a small seasonal habit: walk your trees twice a year, once in midsummer and once in midwinter, and note what has changed rather than what you see on the day. A tree that looks slightly thin this year may simply be recovering from a dry spring.

Reach for the phone when the change is quick — a crown that thinned noticeably in a single season, a bracket that has appeared at the base, a new lean, a crack you can hear ticking on a hot day, or dead limbs hanging over a path, shed, or parked car. Those are jobs for an experienced arboriculturist, not a pair of loppers and a ladder. Trees are forgiving of being looked at, and most of them live a very long time with a hole in them, a few dead branches and a fungus quietly getting on with its work. Your job is simply to notice when the balance shifts.