(Editor's Note: This article was originally published on March 28, 2009. Your comments are welcome, but please be aware that authors of previously published articles may not be able to respond to your questions.)
It is not very often that I have been able to write about a plant that does better in my climate of Newfoundland, Canada than in most other areas of North America, but we do have a tree that we grow to perfection. It is called the goldenchain tree or Laburnum. This small-sized tree (to about 7 m) is a member of the pea family, Papilionaceae. There are only two species, the alpine goldenchain, L. alpinum and the common goldenchain, L. anagyroides and the hybrid between them called L. x watereri. As a rule, these trees are somewhat umbrella-like in habit. The bark is smooth and often green. The leaves are very distinct, being trifoliate like clover or strawberries. In May or June, plants produce a profusion of long 12- to 24-inch pendant chains of bright yellow pea-like flowers that are pleasantly fragrant. The flowers are somewhat reminiscent of Wisteria (albeit yellow not purple-blue) and often bloom at the same time. They do have a couple of negative points: they have no appreciable fall colour, the flowers are messy as they fade and, as a warning, all parts of the plant are extremely toxic. In the wild, they hail from south-central and south-eastern Europe, often in mountainous regions where soils are limestone-based.
The difference between the two species is subtle. Generally, the leaves of L. alpinum are smoother, less hairy on the undersides, than L. anagyroides. The growth habit of L. alpinum is more shrubby and shorter with flower racemes nearly twice the length of those of the other species. Laburnum alpinum is also a tad hardier. The habit of L. anagyroides is more stately as they often form single-trunk specimens. Both species have weeping forms called ‘Pendulum'. The best of both worlds is in their hybrid L. x watereri ‘Vossii', which has longer, more dense racemes than either parent species.
Goldenchains are extremely popular in Europe but are almost unknown in North America. Why is that? They are only reliably hardy to zone 5, which would preclude many areas of central North America. However, even throughout the New England and southeastern states, this tree is uncommon or unknown. Goldenchains are tolerant to a wide variety of soil types (except poorly drained sites) and will withstand considerable wind exposure, roadside/coastal salt-spray and industrial pollution. They are easy to grow from seed and even large specimens will transplant with relative ease. In my region, few insects or disease seem to bother them. They seem the perfect tree! Despite this, about the only areas outside of Newfoundland and coastal Nova Scotia, where this tree is known to any degree is coastal Oregon, Washington and British Columbia. The problem with this tree is that it dislikes hot summers. To thrive, they need temperate summers with little temperature extremes. That describes Newfoundland to a tee! Temperatures above 30 C (85 F) and this tree starts to suffer. We rarely reach that warm in Newfoundland but most of North America commonly exceeds that in summer. Europe, on the other hand, has less extreme summer heat than North America, hence Goldenchains thrive in their climate too. Another problem with Goldenchains is that their thin, smooth bark makes them susceptible to winter bark splitting under sunny conditions. Newfoundland, coastal Pacific Northwest and much of Europe have such cloudy winters that bark splitting rarely causes a problem.
So I hate to say that most North American gardeners will have to enjoy this tree vicariously through us who hail from cool summer-cloudy winter regions. As a consolation, many North American gardeners can grow a wider diversity of ornamental plants than I can, so please forgive my gloating in my ability to grow this wonderful flowering tree!