Heartwood Groves

Hanging a tag

A memorial tag is a piece of hardware fixed to something alive that will outgrow it. None of this is complicated. The mistakes are just slow, and by the time one shows, the tree has been living with it for years.

What follows is what arboreta, tag makers and arborists actually do. Where they disagree, this page says so rather than picking a winner. Sources are at the foot.

The tag that never touches the tree

The Tennessee Urban Forestry Council puts free-standing labels first: a metal or wood stake set in the ground beside the tree, ahead of anything fixed to the trunk. A stake costs the tree nothing at all. National Band and Tag sells them at three quarters of an inch by twenty inches and mounts the tag near the top, so a visitor does not have to crouch to read it. A post set in soil or concrete does the same job and stands up to mowing better.

The trade is that a stake can be mown down or lost under snow, and it does not say this tree as plainly as a tag on the trunk does. If contractors mow your grove, expect to replace a stake at least once.

Hanging from a branch

If the tag goes on the tree, a loose loop of wire over a lateral branch does the least harm. The Arnold Arboretum in Boston has been labelling its collection since the 1870s and uses 22 gauge electrical wire: seven twists to start, a generous loop around the branch to leave room for growth, then seven more turns.

A branch thickens the same way a trunk does, so no loop is permanent. The Tennessee Urban Forestry Council asks for an inspection every two years on a branch-hung label, and every year on anything fixed to the trunk.

How much slack

This is the part people get wrong, because a loop that looks generous today is tight in a few seasons.

An oak puts on roughly 0.2 to 0.5 inches of diameter a year. A willow can beat an inch. Circumference grows about three times as fast as diameter, so the wire has to cover somewhere between half an inch and an inch and a half of extra girth a year on a slow tree, and three inches or more on a fast one. Five years of a young maple is most of a hand's width.

Leave the loop several inches of slack, more on a young or fast-growing tree, and open it out whenever it stops sliding freely on the branch.

Fixing to the trunk

Arboreta do fix labels to trunks, and they are honest about the cost. The Arnold Arboretum drives a three inch stainless screw into the base of the trunk on trees and large shrubs, and wires the label to it.

National Band and Tag builds its method around growth instead: a three inch aluminium nail an eighth of an inch thick, through a stainless spring two and an eighth inches long, into a hole of five thirty-seconds. The tag stands off the bark and the spring compresses as the trunk expands, so the tree grows past the tag rather than around it. They warn against swapping the nail for a screw, which draws the spring flat and takes away the one thing making it work.

The Tennessee Urban Forestry Council no longer recommends the screw and spring at all, and says nailing a label to a trunk injures the tree and disfigures it over time.

What a fastener costs is not in dispute. Trees do not heal wounds the way animals do. They compartmentalise: they wall the damaged wood off and grow around it, so the injury stays inside the tree for the rest of its life, and the hole gives decay organisms a way in. Arborists ask for as few fasteners as possible and would rather you left trees under ten inches in diameter alone.

Nobody has a method that costs the tree nothing, except the one that does not use the tree.

What never to do

Never put wire, cable or cord tight around a trunk or a branch. Bark grows over it, the constriction stops sap moving, and everything above the wire dies. Foresters girdle trees this way on purpose when they want them dead.

Never use a fixing you cannot loosen later, and never fit one and walk away. If you use a strap rather than wire, arborists ask for at least an inch and a half of width so the load spreads instead of cutting a line into the bark.

The yearly check

Walk the grove once a year. On a trunk-mounted tag, look for bark rising around the fastener, or the tag pressed flat against the bark where it used to stand off. On a branch loop, take hold of the wire and see whether it still slides. If it does not, open it out.

Two years is the outside limit for a branch loop. Anything fixed to a trunk wants looking at every year.

What to make the tag out of

For metal, stainless steel in grade 304 or 316 gives the best mix of corrosion resistance and strength outdoors, with anodised aluminium behind it. Keep the tag and its fastener in the same metal family. Brass against aluminium eats the aluminium wherever water sits in the joint, and a stainless fastener joining brass to aluminium corrodes both where they meet. If you have to mix metals, break the contact with a nylon or rubber washer.

For a printed plaque, ASA is the filament to use. It holds its colour and its strength through years of sun and rain. PETG survives outdoors but yellows, stiffens and grows surface cracks over time. PLA is the least UV-stable of the three and will not last a season in full sun, so keep it for a tag you intend to replace.

Sources

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