Laburnum Tree Overview
|Official Plant Name||Laburnum|
|Common Name(s)||Laburnum Vulgare, Laburnum x Watereri, Golden Chain/Rain Tree|
|Flowers||Bright yellow pea-like flowers|
|When To Sow||September, October|
|Flowering Months||May, June|
|When To Prune||February, March|
Exposed or Sheltered
4 – 8M
4 – 8M
May – June
Most Soil Types
Laburnums are small ornamental trees with intensely green foliage. The flowers are even more ‘intense’ in their own way. Bright golden-yellow links, as if in a chain, tumble and dangle in and from the crown of Laburnum Trees in thick, dense clusters, presenting a stunning sight in summer. Indigenous to Southern Europe, the ‘Golden Chain Tree’ is also prized for its high-grade wood.
Laburnums are small flowering trees. However, some descriptions – such as the one in Encyclopaedia Brittanica – do not refer to Laburnum as a ‘small tree’ or a ‘flowering tree,’ but, as a poisonous tree. And with good reason: all parts of this tree, especially the seeds and seed-pods, are very poisonous. They are also very decorative and produce a brief but marvellous show in the summer.
Laburnums are deciduous trees. They attain heights of 5 to 8 metres, with 7 metres-and-change being a common height. This genus has only three accepted species and several cultivars of which one has become predominant and is so renowned that it is identified by the single word, ‘Vossii.’
The three species’ leaves have somewhat different colours, and they also vary as to whether they are smooth or hairy on the underside. All species’ leaves are trifoliate – that is, each leaf is made up of three leaflets. Such leaves are also called ternate leaves. The leaflets are lanceolate to ovate and are 2 to 3 centimetres.
Though the summer show does not last very long at all, there is a show and the flowers are the stars of the show, which is a spellbinding one. For about a fortnight – three weeks if you are lucky – the tree produces thick, lush bunches of flowers that appear inter-connected. These racemes dangle from the branches or cascade or tumble over whatever architectural structure branches have been trained against. The hue ranges from a bright, cheery yellow to a deep, golden yellow.
Racemes vary in profusion, density and length by variety of Laburnum. On the species, the lengths of the racemes range from 12 to 25 centimetres. However, on the most popular and beautiful of the cultivars, the aforementioned Vossii or Laburnum × watereri ‘Vossii’, they reach the amazing length of 60 centimetres. Call them ‘showstoppers.’
The flowers are highly scented; however, the scent is an interesting and perhaps a heady one rather than a sweet perfume.
Left alone, Laburnum will grow to be a small, highly-branched tree. It can be pruned and trained to grow as a shrub, or as an erect tree with a branchless trunk and a heavy crown.
Besides being poisonous and requiring some pruning, Laburnums are susceptible to quite a number of pests and diseases. As such, it is a high-maintenance plant.
Background and Origins
Laburnums are native to a belt of Western and Southern Europe from France and Germany through Italy and Greece to Romania, and spanning the Alps and the Balkans. It arrived in the United Kingdom in 1560, and quickly established itself as a desirable ornamental tree.
Genus Laburnum is a member of Family Fabaceae – the Pea Family or Legume Family. It has only three confirmed species: Laburnum alpinum, Laburnum anagyroides, and Laburnum watereri (Wettst.) Dippel. The last-named arose from a hybrid; however, nearly all Botanical and Dendrological authorities, including Kew and World Flora Online, name it as an accepted species.
Also named within the genus are nearly 50 unresolved and little-known species plus several hybrids and cultivars nearly all of which have come and gone with the seasons.
Both Laburnum alpinum and Laburnum anagyroides when grown as trees attain heights from 4 to 8 metres, reaching ultimate heights after about 20 years. Their spreads too are from 4 to 8 metres.
Laburnum alpinum is also called ‘Scotch laburnum’ or ‘Scottish laburnum’ but not because it is ’Scottish’! Apparently the Scots appropriated the tree and somehow named it because they valued – and continue to value – its wood, and particularly its heartwood, for – among other uses – making bagpipes. In contrast, poor Laburnum anagyroides is only called ‘Common laburnum’!
Both species bloom in late May and the beginning of June. L. alpinum racemes at 35 to 40 centimetres are very long compared to those of L. anagyroides which are 15 to 20 centimetres. On the other hand, L. anagyroides racemes are denser and thicker. In autumn highly poisonous seed pods form from the withered flowers.
Another point of difference is the foliage. L. alpinum’s leaves are a crisp dark green whereas those of L. anagyroides are a dull greyish-green. The former’s leaves are glabrous or smooth while the latter’s are pubescent – they have fine downy hair on the underside.
Among the numerous cultivars that have come and gone, one stands out for each of the species. L. alpinum ‘Pendulum’ is so named because its branches are pendulous, which enhances the ‘dangling gold chain’ effect when the tree is in bloom and the ‘weeping’ boughs move in the wind. Another reason it stands out is because it is a dwarf variety reaching an ultimate height and spread, both, of only 1.5 to 2.5 metres.
L. anagyroides ‘Sunspire’ is also a dwarf but it has a narrower, fastigiate form, attaining an ultimate height of 2.5 metres with a spread of (only) 1 metre. Like its parent, the racemes are short but dense. Upon emerging the racemes are erect and stay erect for about a fortnight.
Hybrids arose naturally from the two ‘main’ species, including in Great Britain, and they are collectively called L. watereri. Laburnum watereri (Wettst.) Dippel is recognised as a distinct species that developed from a cross. However, the most desirable and most well-known Laburnum is a cultivar, L. × watereri ‘Vossii.’ It is the only Laburnum variety to have received the R.H.S.’s Award of Garden Merit.
A ‘watereri’ hybrid that occurred in the wild in the Tyrolean region was found in the 1850s and brought to the Netherlands where ‘Vossii’ was cultivated from it in the late 1800s. Like its parent species, it attains an ultimate height and spread of 4 to 8 metres.
Overall, ‘Vossi’ exhibits a few characteristics of each parent. Consider: both the young stems and leaflets are initially pubescent but become glabrous as they mature. In general, ‘Vossii’ brings together the best attributes of each parent and introduces a couple of new ones. It produces far fewer seed pods, each of which has fewer (poisonous) seeds. Even the foliage is a more appealing shade of green, being less grey and less dark. As for the racemes, they are spectacular. The flowers’ hue is a rich golden yellow, they are dense and lush, and they are 50 to 60 centimetres long. The spectacle lasts from two to three weeks.
L. × watereri ‘Vossii’ is the most popular Laburnum variety in the U.K. and in other countries as well.
Giving some competition to the Laburnum is another ‘Laburnum’ – the ‘Indian Laburnum,’ or Cassia fistula which is, obviously, a species of a different genus, Cassia.
Laburnum and Cassia trees do look quite similar in the flowering season when Cassia trees are also covered by a profusion of drooping, thick racemes of small, bright yellow flowers. In fact, Cassia too is a member of Family Fabaceae.
Cassia trees are of considerable cultural significance in Thailand, Laos, Sri Lanka, and India. Besides Tropical East Asia, their native range spans the Equatorial and Tropical regions of Africa and South America. Evidently, these trees’ climate preferences are very dissimilar to the ones it is physically so similar to. Among the nearly 40 species, a good few are native to even some of the hottest regions of the planet. For instance Cassia sieberiana grows in Western Africa from Mauritania and Liberia to Niger and Nigeria.
Then there is a ‘Nepal laburnum’ – Piptanthus nepalensis, with the genus (Piptanthus) also being a member of the Fabaceae family. This Himalayan native also puts on wonderful summer shows but its yellow-flowered racemes are only 4 centimetres short. However, it too is quite popular in European countries because, though its racemes’s length is a small fraction of those of even Laburnum anagyroides, what to speak of ‘Vossi,’ unlike Genus Laburnum’s species, Piptanthus nepalensis is tough, pest-resistant and disease-free, and, therefore, low care.
Finally, we have “Adam’s laburnum” – botanical name, + Laburnocytisus ‘Adamii.’ This wonderful curiosity is a hybrid of Laburnum and Purple Broom with the result that in the spring flowering season, some branches are thick with yellow Laburnum racemes while other branches bear Purple Broom flowers!
When and Where to Plant Laburnum Tree
Laburnums should be planted in spring, preferably mid or late spring.
Laburnums are curiosities because they are average small trees for eleven months of the year but for nearly one month they are an ‘A+’ in ornamental value.
They are sometimes planted in neat rows. They are commonly trained so that the branches grow over an arch or any wall, or grow flat over a lattice roof of a pergola so that in flowering season it creates a golden-chain ceiling.
These small trees often benefit from a sheltered location, especially in cold and blustery regions. As their roots are non-invasive, they can be grown right beside all kinds of structures, such as a patio or boundary wall. Of course, they can also be planted right beside the house but one must be mindful that this is a poisonous tree.
Habitat & Growing Conditions
As natives of Western and Southern Europe Laburnums prefer cooler climes and are not exactly tolerant of high heat or humidity. They are also not tolerant of frigid weather, as may be inferred by their USDA Hardiness Zones. Hardiness zones for the species are 5 to 7, and for ‘Vossi,’ 6 to 8. Cool summers and moderate winters are ideal for Laburnums.
In colder climates or regions that do not get sunny and hot in the summer, Laburnums should get full sun. Otherwise, they should be protected from the midday and afternoon sun. Latitude also dictates where you should grow a Laburnum. Up in County Ross it should be grown in full sun; down in Gibraltar, in part sun.
Feeding, Care & Growing Tips
Laburnums are best planted in autumn. Young trees need support and should be staked. Though these trees are not fussy about soil, start them off with some compost or manure.
Laburnums grow well in any soil as long as it is not too acidic or too alkaline; pH Slightly Alkaline to Slightly Acidic soil will do just fine. A good loam mix is ideal. Soil should be very well drained; above all, Laburnums will not tolerate waterlogged soil.
Mature plants should be watered once a week or very lightly twice a week. Though Laburnums are fairly drought-tolerant, in hot climates the soil should be kept moist in spring and summer.
It may be fertilized every spring with an organic 10-20-10 or a rich compost.
Pruning Laburnum Tree
Laburnums can be grown as bushy shrub, a fastigiate tree, and anything in between. It depends on how you prune and train it.
If you would like to grow the relatively unusual Laburnum shrub, on the young tree cut back the leader but let the secondary stems grow. If you would like it to grow tall and erect, prune all secondary stems.
In either case, when it is a sapling you will need to stake it.
When to prune, though? Some experts opt for late-summer when the flowering season is over and the tree is growing and full of life. Others propose winter when the tree is dormant and growth is at a halt. However, we know when not to prune Laburnum. Do not prune in spring or early summer as the tree will ‘bleed’ and it will be susceptible to infections.
What you should ‘prune’ are the seed pods, and for dual reasons at that. To begin with, they are not exactly decorative. More importantly, they draw away the vigour of the tree. And most importantly they are the most poisonous part of the plant.
Common Diseases & Problems
All Laburnum varieties are very prone to pests and diseases. Pests include snails, aphids, mealybugs, and leaf miners – all three, Lepidoptera, Diptera, and Hymenoptera. Diseases include canker, twig blight, leaf spot, powdery mildew, and silver leaf.
At least most deer will steer clear of Laburnum – most, but not all!
Obviously, Laburnums are not low-care trees.
You will need to learn about medications like BotaniGard ES, Safer’s soap, and Orthene solutions, and counteracting organisms such as beneficial nematodes, lacewings, and mealybug destroyers.
Infestations like powdery mildew and twig blight can just about only be resolved by cutting off affected parts of the tree with sterilised pruning implements.
Laburnum is Poisonous
Laburnum is toxic in varying degrees from root to shoot, with the seeds being particularly poisonous. For this reason households with children and pets should be very wary about growing this tree.
The symptoms of poisoning can be quite distressing and extreme. Nausea, diarrhoea and vomiting are almost always observed, as are drowsiness and lethargy. Sometimes convulsions also occur. Fatalities are uncommon but not rare.
The poisonous substance is cytisine which is one of the toxic alkaloids that is produced in some plants.
Uses of Laburnum Wood
In general, Laburnum trunks yield a high-quality wood, and L. alpinum heartwood is one of the most sought-after woods. It is very hard, has an appealing yellowish-brown colour, is very shiny and can be polished to a lovely sheen. With such a list of attributes is it any wonder that this wood is described as ‘highly prized’?
L. alpinum wood, particularly the heartwood, is one of the top choices for cabinet-making and parquetry. Flutes, recorders, and bagpipes used to be made almost exclusively with Laburnum wood, and these musical instruments are still made from this wood, among others.
Where to Buy
Laburnum × watereri ‘Vossii’ is widely available and is very easy to find in nurseries and garden centres. The three species are also available, though at a more limited number of nurseries. Specialist nurseries offer one or two of the old, established cultivars and one or two newer ones.