In short
- Grows to 4–7 m tall and 3–6 m wide — it fits even in a small garden.
- Flowers in May with drooping, golden-yellow racemes 10–30 cm long.
- Highly poisonous: cytisine occurs in every part, most of all in the seeds and pods.
- Likes sun and free-draining soil, including dry, poor and limy ground; it does not tolerate waterlogged sites.
- Formative pruning only in late summer or early autumn — in winter and spring it bleeds sap heavily; spent racemes with pods are removed separately, already in June.
Botanical data
- Family
- Fabaceae (Fabaceae)
- Height
- 4–7 m
- Width
- 3–6 m
- Habit
- Spreading
- Growth rate
- Moderate
- Position
- Full sun, Partial shade
- Soil
- Sandy, Loamy, Chalky, Humus-rich
- pH reaction
- pH 5.5–7.8
- Moisture
- Dry, Moderate
- Bloom
- May–June
- Hardiness
- USDA 5b–8a
- Propagation
- From seed
Characteristics
A small tree or large, often multi-stemmed shrub, at first upright in habit and with age broadly spreading, with arching main branches. It usually reaches 4–7 m in height and 3–6 m in width, grows at a moderate rate and is short-lived — in gardens it most often lives 20–40 years. The bark of young trunks is smooth and olive-green, becoming grey-brown and shallowly fissured with age, while the heartwood is dark, almost chocolate-coloured. The leaves are trifoliate, borne on long stalks, with elliptic leaflets 3–8 cm long, dull green above and — like the young shoots and pods — covered beneath with appressed, silky hairs. This hairiness is the simplest feature distinguishing the species from the very similar Scotch laburnum (Laburnum alpinum), whose leaves and fruits are almost hairless and glossy. The pea-like, golden-yellow flowers, gathered several dozen at a time in drooping racemes 10–30 cm long, open in May — in cooler years and at higher elevations at the turn of May and June — after the leaves have unfurled; Scotch laburnum flowers two to three weeks later. The tree is not grown for fragrance: its ornamental value rests entirely on the effect of the drooping racemes. The fruit is a flattened pod 4–8 cm long, at first green and silkily hairy, and after ripening in August and September brown and papery, containing several hard, dark seeds; empty pods can hang on the branches into winter. As in other legumes, nodules containing bacteria that fix atmospheric nitrogen form on the roots.
Popular cultivars
- ‘Pendulum’
- A form with drooping, arching pendent shoots, propagated exclusively by grafting onto a standard — its ultimate height depends on the height of the rootstock and usually does not exceed 2–3 m. It flowers like the species, but the racemes hang along the cascade of shoots. It requires the systematic removal of shoots emerging below the graft union.
- ‘Aureum’
- A cultivar with yellow-golden leaves, most intensely coloured in spring and fading to yellow-green in summer. It grows more slowly and remains distinctly smaller than the species; in full sun the leaves are sometimes scorched, so it copes better in light partial shade. Rare in the trade.
Growing and care
Watering
Once established it withstands periodic drought and poor, stony soils; regular watering is required only by young specimens for the first two to three seasons. It reacts very badly to standing water — wet, compacted ground is a common cause of shoot dieback.
Fertilizing
Sparingly and without nitrogen — laburnum, as a legume, lives in symbiosis with root-nodule bacteria that fix atmospheric nitrogen, and nitrogen feeding builds up shoots at the expense of flowering.
Planting
A sunny site or in light partial shade, free-draining soil — including poor, stony and limy ground. Avoid boggy, compacted spots and hollows where water collects.
Pruning
Formative pruning is minimal — remove dead, diseased and crossing shoots, and individual branches that disturb the habit. Independently of this, spent racemes are cut out each year in June together with their stalks, before the pods turn brown: this limits the amount of poisonous seed in the garden and strengthens flowering the following year. On forms grafted onto a standard, unconditionally remove shoots emerging below the graft union.
Companion plants
Good companions
Czosnek olbrzymi zakwita w czerwcu, gdy złotokap kończy kwitnienie — fioletowe kule przejmują wtedy efekt pod prowadzonym na łuku tunelem i przedłużają go o kolejne tygodnie. Obie rośliny lubią pełne słońce i przepuszczalną, niezbyt wilgotną glebę.
Znosi suchą, przerośniętą korzeniami ziemię w lekkim cieniu pod koroną i tworzy zwartą okrywę bez konkurowania o wodę z drzewem.
Na słonecznym obrzeżu, poza zasięgiem korony, ma te same wymagania co złotokap — pełne słońce, przepuszczalną, zasadową glebę i suche lato — a kwitnie w maju i czerwcu, więc towarzyszy gronom przez cały ich okres.
Bad companions
Opadające kwiaty, a zwłaszcza dojrzewające strąki z silnie trującymi nasionami mieszają się z jadalnymi zbiorami — to realne ryzyko przy grządkach pielęgnowanych razem z dziećmi.
Różanecznik wymaga kwaśnego, stale wilgotnego i próchnicznego podłoża, a złotokap najlepiej rośnie na przepuszczalnej, suchej, często wapiennej glebie — jednego stanowiska nie da się przygotować pod obie rośliny.
The evidence level indicates whether the relationship is backed by research, observation, or gardening tradition.
Diseases and pests
The fungus attacks the roots and stem base of trees and shrubs, causing their slow decline – the plants grow weakly, the crown thins, the leaves become smaller, and eventually they dry up. The diagnostic sign is white, fan-shaped sheets of fungal mycelium forming a dense layer under the bark at the stem base, with a distinct mushroom smell. In the soil and under the bark there are black or dark-brown, bootlace-like rhizomorphs, by which the fungus spreads to further plants. In autumn, clusters of fruiting bodies – honey mushrooms – grow at the base of infected trees. The above-ground symptoms are non-specific and easily confused with drought or overfeeding: some plants die suddenly (the whole tree turns brown within a single season, especially in hot weather), while others weaken over years – producing short growth, discolouring prematurely, and just before death setting an exceptionally heavy crop of flowers or fruit ('stress flowering'). In conifers, resin bleeding at the stem base is common. When the bark is exposed at the root collar, the wood of the roots and stem turns white and softly rots – honey fungus causes a white rot of the wood. The mycelial layer can be cream-coloured and leathery, spreading radially from beneath the dead bark. A biological curiosity, rather than a sign useful in garden diagnosis, is that the mycelium in moist, infected wood can glow very faintly in the dark (so-called 'cold light') – the effect is too weak and requires complete darkness, so in practice it cannot be used to identify the disease. The disease advances in foci – neighbouring plants die off one after another around an infected one.
AphidsSmall (1–3 mm) soft-bodied insects, green, black or pink, feeding in clusters on young shoots and the underside of leaves. They excrete sticky honeydew. The diagnostic feature that distinguishes aphids from other small sucking insects is the pair of siphunculi (tubular projections) at the rear of the abdomen together with a tail-like cauda; a single colony usually holds wingless forms (parthenogenetic females) alongside winged migrants that fly onto new plants in summer. In summer aphids reproduce parthenogenetically and viviparously over many generations, so the population builds up explosively; in autumn many species produce a sexual generation that lays overwintering eggs on the host, and host-alternating species move between a winter host (often a tree or shrub) and a summer host (a herbaceous plant). Feeding symptoms include curling, crinkling and distortion of young leaves, stunted growth, yellowing, and the shedding of buds and fruitlets. Abundant honeydew coats the leaves, and the sooty mould fungus that develops on it forms a black film which limits photosynthesis; the honeydew is fed on by ants, which in return defend the colony against predators. Aphids are also important vectors of plant viruses (mosaics among them), transmitting them from plant to plant even during a brief probing puncture.
Toxicity
| For whom | Level | Notes |
|---|---|---|
| Humans | High | Every part contains cytisine — a quinolizidine alkaloid acting on the same nicotinic receptors as nicotine. It is most abundant in the seeds and unripe pods. Symptoms (nausea, vomiting, abdominal pain, sweating, dizziness, a racing pulse and, in more severe cases, convulsions) usually appear within an hour. If seeds are suspected to have been swallowed, call 112 or a poison control centre immediately. |
| Dogs | High | Eating the pods or seeds causes vomiting, drooling, muscle tremors and rapid breathing — it requires urgent contact with a veterinarian. |
| Cats | High | — |
| Horses | High | Browsing on the shoots, leaves and bark can be life-threatening for horses. The tree is not planted near paddocks, pastures and fences through which animals can reach for branches. |
History and origin
The species comes from the mountains of southern and central Europe — from France and the southern Alps to the Apennines and the Balkans — where it grows on open, stony slopes, often on limestone. In Poland it occurs only in cultivation and only occasionally escapes from plantings. The genus name was taken directly from Latin: Pliny the Elder already used the word laburnum for this tree. The species epithet anagyroides means "resembling anagyris" and refers to the Mediterranean shrub Anagyris foetida; the present name was given to the species in 1787 by the German botanist Friedrich Kasimir Medikus. In the gardens of Western Europe laburnum was cultivated from at least the second half of the sixteenth century, and it reached the peak of its popularity in the nineteenth century, when it became a fixture of landscape parks and townhouse gardens — that was also when laburnum tunnels trained over arches became widespread. A separate thread concerns chemistry. Isolated from the seeds in the nineteenth century, cytisine proved to be a quinolizidine alkaloid acting on the same nicotinic receptors as nicotine, which explains both the symptoms of poisoning and the substance's later career in pharmacy. It is reported in the literature that smoking dried laburnum leaves as a tobacco substitute in Central and Eastern Europe during the Second World War led researchers to its pharmacological use. This was a desperate and dangerous practice — the smoke carries cytisine, the very alkaloid responsible for laburnum poisoning; today it has no application and must not be repeated.
Uses
Laburnum is planted as a specimen on a lawn or trained over an arched structure to form a tunnel beneath which a curtain of golden racemes hangs in May; the classic underplanting for such a walkway is tall ornamental alliums — their purple globes open, depending on the species, from May to July, so they take over the effect as the laburnum racemes fade. The site should be sunny or at most in light partial shade — in shade the tree flowers sparsely. Soil: free-draining, willingly stony, poor and limy; the plant tolerates a wide range of pH, from slightly acidic to alkaline, but does not tolerate waterlogged and compacted ground. It grows well in urban conditions. It is planted in October or in March and April, at a spacing of 3–5 m from its neighbours; nitrogen feeding is unnecessary, because laburnum fixes nitrogen itself thanks to root-nodule bacteria. It is worth remembering that this is a short-lived tree — it is not planned as a dominant feature for decades. Formative pruning is kept to a minimum and carried out in late summer or early autumn (August–September), because when cut in winter and early spring laburnum bleeds sap heavily. A separate, annual task is the removal of spent racemes with their pods, and it has its own, earlier date: right after flowering, in June, while the pods are still green. Postponing this to the August pruning defeats the purpose, because the seeds ripen precisely in August and September, and the pods begin to fall at that time. Ornamental cultivars, including the weeping 'Pendulum', are propagated by grafting onto a standard, so all shoots emerging below the graft union must be cut off right at the base; the species itself is propagated from seed, which is scarified or soaked before sowing, because it has a hard, poorly permeable coat. The siting, however, is decided above all by toxicity. Laburnum is not planted near playgrounds and in nursery-school gardens, nor over vegetable and herb beds, where falling pods mix with edible harvests. Nor should it grow beside paddocks for horses, cattle and goats. In a garden visited by small children the tree is planted out of reach of play and the pods are consistently removed while still green, before they begin to fall.
Trivia
- Cytisine, the alkaloid responsible for laburnum's poisonous properties, is at the same time the active substance of a smoking-cessation drug registered in Bulgaria in 1964; it also served as the chemical template for the development of varenicline.
- Pliny the Elder, describing the Alpine tree called laburnum, noted that bees avoid its flowers. Laburnum is indeed a poor nectar plant — its flowers are opened above all by bumblebees, strong enough to prise apart the keel of the pea-like flower.
- Laburnum's dark heartwood is sometimes called "false ebony" (faux ébénier) in France; it was formerly used to make inlays, small turned objects and parts of wind instruments.
- The most famous laburnum tunnel grows in the Welsh garden of Bodnant — the planting was laid out in 1880, and the walkway is about 55 metres long.
Frequently asked questions
Is laburnum dangerous to children?
Yes — it is one of the most poisonous ornamental trees in our gardens. Every part contains cytisine, an alkaloid acting on the same receptors as nicotine, with the highest concentration in the seeds and unripe pods, which look like little pea pods and are sometimes put in the mouth. The symptoms — nausea, vomiting, abdominal pain, sweating, dizziness and a racing pulse — usually appear within an hour. If seeds are suspected to have been swallowed, do not wait for symptoms: call 112 or a poison control centre. In a garden with small children the tree is planted out of reach of play and the pods are consistently cut off right after flowering.
When and how should laburnum be pruned?
Formative pruning is carried out in late summer or early autumn (August–September) and only to a minimal extent. When cut in winter or early spring, laburnum bleeds sap heavily, which weakens the tree and hinders the healing of wounds. Dead, diseased and crossing shoots are removed, along with individual branches that spoil the habit; the plant tolerates hard shortening and reduction of the crown into old wood poorly. A separate task, with its own and earlier date, is the removal of spent racemes with their pods — this is done in June and is not combined with the August pruning. Cultivars grafted onto a standard, such as 'Pendulum', additionally require the removal of all shoots emerging below the graft union.
Do the pods have to be removed after flowering?
It is worth doing, for two reasons. First, the seeds are the most poisonous part of the plant, and cutting off the pods before they ripen and begin to fall is the simplest way to reduce the risk in a garden with children or animals. Second, heavy fruit set costs the tree a lot of energy and weakens flowering the following year. Spent racemes are cut off together with their stalks in June, while the pods are still green. It is not postponed to the August formative pruning — by then the seeds are already ripe and the pods are beginning to fall, so the task loses its main point.
Why does laburnum not flower, or flower poorly?
The most common causes are too young an age (seedlings flower only after several years, grafted specimens earlier), too much shade, and pruning at the wrong time — shortening shoots in winter and spring removes the set flower buds. Flowering is also weakened by heavy fruiting in the previous season, which is why it pays to remove the pods, and by an excess of nitrogen: laburnum, as a legume, fixes nitrogen itself and, when fed with nitrogen, builds up shoots at the expense of flowers.
How does common laburnum differ from the popular cultivar 'Vossii'?
'Vossii' is not a cultivar of this species but of the hybrid Laburnum × watereri, arising from a cross between common laburnum and Scotch laburnum (Laburnum alpinum). It has distinctly longer racemes, reaching 50–60 cm, and sets few seeds, which is why it is most often chosen for tunnels and pergolas. The species itself flowers slightly earlier, and its racemes are 10–30 cm long. Note: fewer seeds does not mean the hybrid is non-toxic — cytisine is present in every part of the plant.
Sources
- Plants of the World Online (POWO)Database (GBIF, POWO…)
- RHS — Laburnum anagyroidesInstitution / botanical garden
- EFSA — Compendium of botanicals reported to contain naturally occurring substances of possible concern for human healthInstitution / botanical garden
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