Laburnum: Golden Chains and Deadly Seeds

What it is

Laburnum anagyroides and L. alpinum, small trees of the mountains of central and southern Europe, and their hybrid L. × watereri, which is the one most often planted.

A legume, in the broom and pea group with gorse and the brooms, and it shows the family in its pea-shaped flowers and its pods. In late spring and early summer it hangs with long, dense, pendulous chains of bright golden-yellow flowers — the golden chain tree — one of the most spectacular flowering displays of any hardy small tree.

Every part is poisonous

The defining caution, and it governs where laburnum can sensibly be planted.

The whole plant — especially the seeds — contains cytisine, an alkaloid related to nicotine, and it is genuinely toxic. Poisoning causes vomiting, drowsiness, convulsions, and in severe cases can be fatal, and the pea-like pods and seeds are exactly the kind of thing children pick and eat, mistaking them for peas.

In practice serious poisonings are rarer than the fearsome reputation suggests — most cases are mild and recovery is usual — but laburnum is one of the more genuinely dangerous garden plants, and it is a poor choice near young children, playgrounds, or livestock. Horses and other animals are also poisoned by it.

Cytisine is not only a hazard: it is used medically as a smoking-cessation aid — it acts on the same receptors as nicotine — and it has a long history in eastern Europe as exactly that, a reminder that many plant toxins are also drugs, as with the yew and its cancer medicine.

Because it is a legume, laburnum does fix nitrogen, though it is grown as an ornamental rather than for soil improvement. See nitrogen fixers.

The laburnum tunnel

Laburnum's flowering is dramatic enough that it is grown as a garden set-piece: the laburnum arch or tunnel, in which trees are trained over a curved framework so the golden flower chains hang down inside, creating a corridor of gold in early summer. The tunnels at Bodnant in Wales and elsewhere are famous, and it is one of the classic pieces of trained-tree garden theatre, in the manner of the pleached lime and hornbeam walks.

The flowers are worked by bees, though as a short-lived spectacular the laburnum's wildlife value is modest.

The wood

Laburnum has one genuinely useful product beyond its flowers: its timber.

The heartwood is dark, hard, dense, and beautifully coloured — chocolate to greenish brown, sharply demarcated from the pale sapwood — and it takes a fine polish. It was traditionally used as a substitute for ebony, for inlay and decorative work, for wind and stringed instruments (recorders and bagpipes especially), and for turnery and small durable items. The contrast between dark heart and pale sap is exploited in "oyster" veneers cut across small branches. It is one of the finest native European decorative timbers, if only ever available in small pieces.

Growing it

Easy and undemanding: full sun to light shade, and almost any well-drained soil including chalk and poor ground. It dislikes only waterlogging.

Fast-growing but short-lived — 20 to 40 years is usual — with a small size, 5 to 8 m, that suits a garden, and it is often multi-stemmed.

The hybrid L. × watereri 'Vossii' is the usual choice, with the longest flower chains and — a real advantage given the toxicity — it sets few or no seeds, reducing both the litter and the poisoning risk.

Largely free of serious pests and diseases, though laburnum can suffer from a leaf miner and from twig blight.

Grows readily from seed (which perpetuates the seeding problem) and the named forms are grafted. See grafting.

Laburnum is grown purely for its early-summer flower spectacle — few hardy trees match the golden chains — with the caveats about toxicity firmly in mind, and the near-seedless 'Vossii' the sensible choice for most gardens.