Tuesday, 21 December 2010

A tree at Christmas

Chamaecyparis lawsoniana, Siskiyou Mountains, Oregon
'Garden planning in Britain is primarily the study of Lawson Cypress. Other plants are just infilling.' (Alan Mitchell 1996).

One of the botanical highlights of the year for me was seeing Chamaecyparis lawsoniana in the wild when I visited Oregon in early March. Whether one agrees with Alan Mitchelll or not, this is one of the most important of all conifers, not only for its ornamental qualities but also for its excellent timber, which is still very much in demand and rather valuable. Despite its adapatability in European conditions, in the wild it is confined to a small area of southern Oregon and northern California, growing from the coast up into the Siskiyou and Trinity Mountains in those states respectively. It was in the Trinity Mountains that seed was collected in 1854 by William Murray and sent to Lawson's Nurseries near Edinburgh where four seedlings germinated. It was promptly named in 1855 by William's brother, Andrew Murray, in honour of this establishment, presumably on the strength of dried material received with the seeds (though no early specimens are extant). In the following year a larger quantity of seed arrived: some was sown by Lawson, and some by Anthony Waterer in Surrey, with the result that the species quickly became freely available in the British horticultural trade at the peak of the Victorian conifer craze. The result is that it is responsible, according to Alan Mitchell, 'for so much monotonous funereal gloom in suburban parks and gardens.'

The British have always known it as Lawson Cypress, but in the United States it is most commonly referred to as Port Orford Cedar, after the port on the Oregon coast from which much of its timber was shipped. The finest stands close to the coast were logged long ago, though trees of 70 m or so still survive (29 m is the tallest attained in Britain,so far). To the damage done by logging now must be added the ravages of the waterborne rootrot fungus, Phytophthora lateralis, which is killing many trees in the remaining forests, and also makes the species a poor choice for gardens. (It's therefore alarming to hear this week that this disease has been recently found in Scotland, and it is to be hoped that it is swiftly contained.) The trees I saw in the Siskiyou mountains, under the guidance of Sean Hogan, seemed to be free of the disease, perhaps because of the chemical properties of the serpentinite rock on which they are growing. They were certainly reproducing freely, with abundant seedlings springing up (left).

The lack of variation seen in wild trees of Chamaecyaris lawsoniana has been commented on by many authors, usually in contrast to the proliferation of cultivars that have been selected in horticulture. I cannot think of any other plant that has given such an extraordinarily protean diversity of shapes and sizes in its basic morphology. The process started early, with the selection of an 1855 seedling by Waterer that combined an upright habit with lush verdant foliage. This is what we know as the cultivar 'Erecta Viridis' "which disfigures nearly every churchyard in the land", again according to Alan Mitchell, principally because it has a habit of dropping branches. There are some venerable specimens of it at Colesbourne Park, certainly of Victorian planting, that have avoided the fate of becoming too ragged and still present an attractive sight. In the picture below an old tree is visible behind a younger specimen. Variegated seedlings also appeared quite promptly in nurserymen's seed beds, and numerous selections have been made over the years. An early one was 'Lutea', selected in about 1870: again, there is a fine specimen at Colesbourne (below). Sparingly used, these yellow conifers are of inestimable value, bringing rich colour to the winter landscape.

C. lawsoniana 'Erecta Viridis'
C. lawsoniana 'Lutea'













In all, well over 200 named cultivars have been selected, ranging from really tiny dwarves, that stay as compact buns, to apparently slow-growing, smaller clones that given time can form a monstrous blob, as in the case of one we saw growing at Icomb Place earlier this year (picture below), obscuring half a fine view.  I cannot imagine why nobody has removed it.

C. lawsoniana at Icomb Place

C. lawsoniana 'Blue Surprise'
 There are good blue cultivars, such as 'Pembury Blue' and 'Blue Surprise' (right), which also has the distinction of retaining the juvenile form of its shoots and leaves, as several others in the 'Ellwoodii' complex do.  My favourite cultivar, however, is the extraordinary clone known as 'Imbricata Pendula', in which the shoots have been reduced to long narrow whipcords by a failure to branch. A normal dark green in colour, this is the most see-through conifer I have encountered: I'd love to use it to make the shimmering walls of a bower. Despite its lack of foliage it is surprisingly vigorous, but it does need a stake when young to ensure that the leader has some support.

C. lawsoniana 'Imbricata Pendua' in hoar frost,
December 2010


male cones in early April
One feature of the Lawson Cypress that I particularly enjoy is the display provided by its male cones in spring, with each shoot covered in little red and black blips that look almost like tiny insects. In some cultivars, especially the congested but columnar 'Wisselii', the effect is almost floral (one always has to be careful to make the point that the reproductive organs of a conifer are not flowers, however tempting it is to think of them as such). The male cones, or strobili, produce pollen that fertilizes the female structures, enabling them to develop into the familiar fruiting cones. They are opening now, shedding their seed on the snow.

fruiting cones of C. lawsoniana, early December
The late great dendrologist Alan Mitchell has supplied some humorous quotations for this post, but here is his opening paragraph in which they appear in context (from Alan Mitchell's Trees of Britain, 1996):

'The tree which is responsible for so much monotonous funereal gloom in suburban parks and gardens is nometheless surpassed in no less than three important aspects. In cultivation it is a great deal more variable than any other conifer, despite being singularly uniform in its native stands. It has yielded cultivars of an extraordinary range of patterns of foliage, textures and every colour which is available to a conifer. It is, with its cultivars, the prime tree in garden layouts for shelter, winter colour, backbone and winter form, for eye-catchers and other colour-features, for cover for birds nesting and roosting. It can also be shaped into topiary. It is bone hardy and grows happily on most soils. It is the ideal, general purpose and ornamental tree, with forms available to suit any space.Garden planning in Britain is primarily the study of Lawson Cypress. Other plants are just infilling.'

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