× Cupressocyparis leylandii (Dallim. & Jacks.) Dallim.

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Article from Bean's Trees and Shrubs Hardy in the British Isles

Recommended citation
'× Cupressocyparis leylandii' from the website Trees and Shrubs Online (treesandshrubsonline.org/articles/x-cupressocyparis/x-cupressocyparis-leylandii/). Accessed 2021-09-20.

Synonyms

  • × Cupressocyparis leylandii Dallim. & Jacks.

Glossary

clone
Organism arising via vegetative or asexual reproduction.
article
(in Casuarinaceae) Portion of branchlet between each whorl of leaves.
clone
Organism arising via vegetative or asexual reproduction.
cone
Term used here primarily to indicate the seed-bearing (female) structure of a conifer (‘conifer’ = ‘cone-producer’); otherwise known as a strobilus. A number of flowering plants produce cone-like seed-bearing structures including Betulaceae and Casuarinaceae.
hybrid
Plant originating from the cross-fertilisation of genetically distinct individuals (e.g. two species or two subspecies).
pollen
Small grains that contain the male reproductive cells. Produced in the anther.
pollination
Act of placing pollen on the stigma. Various agents may initiate pollination including animals and the wind.

References

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Credits

Article from Bean's Trees and Shrubs Hardy in the British Isles

Recommended citation
'× Cupressocyparis leylandii' from the website Trees and Shrubs Online (treesandshrubsonline.org/articles/x-cupressocyparis/x-cupressocyparis-leylandii/). Accessed 2021-09-20.

This cross between Cupressus macrocarpa and Chamaecyparis nootkatensis first occurred at Leighton Hall, near Welshpool, at that time the property of a Mr Naylor. In 1888 seed was sown there from a cone of Nootka cypress and of the seedlings six were seen to differ from the rest; they were, in fact, the result of cross-pollination by a tree of Cupressus macrocarpa growing nearby, although this was not appreciated until later. These six were taken by Naylor’s brother-in-law, C. J. Leyland, and planted on his property, Haggerston Hall, Northum­berland, in 1892-3. Five of these still exist and are the parents by vegetative propagation of × C. leylandii, Clones 1 to 5.

About 1911 the same cross was again raised at Leighton Hall, but this time C. macrocarpa was the seed parent and Chamaecyparis nootkatensis the pollinator; from this batch two seedlings were picked out and planted on the property. One of these (Clone 10) was blown down in 1955 but was propagated before its death; the other (Clone 11) still grows on the hill behind the house.

However, these trees did not come to the attention of botanists until 1925. Their hybrid origin and parentage was established by Dallimore and Jackson, who published a description in the Kew Bulletin in the following year, giving the hybrid the name Cupressus × leylandii. But the recognition of Chamaecyparis as a genus distinct from Cupressus necessitated the transfer of the Leyland cypress to the hybrid genus × Cupressocyparis and it first appeared under that name in the Kew Hand-list of Conifers in 1938.

To complete the story, it should be added that the same hybrid was again raised in a Dorset nursery around 1940; the two trees that resulted are the parents of Clones 20 and 21, both of which are in commerce and resemble Clone 11 (‘Leighton Green’) in habit and foliage.

The Leyland cypress is one of the most important tree introductions of recent times, having all the virtues for which Cupressus macrocarpa has been so widely planted and none of its vices. It is, in the first place, of very rapid growth, capable of making a fine specimen 55 to 60 ft high in twenty-five years. Like the Monterey cypress, it is resistant to sea-winds, but whereas the use of that species is restricted to the milder parts, the Leyland cypress inherits from its other parent the ability to resist the worst of our winters without damage and is likely to prove a reliable and fast-growing shelter-belt tree over much of the country. It also makes an excellent hedge plant; its ability to withstand restriction is shown by the flourishing dwarf hedges in the Arboretum nursery at Kew, planted in 1947, which have been kept by mechanical trimming to a height of 4 ft and show no resentment at such drastic treatment. Finally, it makes a fine specimen tree of columnar habit but it is to be hoped that gardeners will not be tempted by its rapid growth into using it to excess.

For the following descriptions of the main clones of Leyland cypress (and for much of the historical account) we are indebted to the study by H. Ovens, W. Blight and A. F. Mitchell in Quarterly Journal of Forestry, Vol. 53, Jan. 1964.

From the Supplement (Vol. V)

The statement in the first paragraph that C. J. Leyland was Mr Naylor’s brother-in-law is incorrect. He was the son of John Naylor (d. 1889) and took the surname Leyland when he inherited the entailed estates of Leighton and Haggerston from his great-great-uncle Thomas Leyland, in 1892. He was probably already managing the Leighton part of the estate for his father when the first Leyland cypresses were sown (1882). These were removed to Haggerston Hall, where he lived. He subsequently sold his life interest in Leighton to his brother John Naylor (d. 1906), whose son Captain J.M. Naylor came to live at Leighton Hall in 1909, staying there until 1931. The second Leyland cross took place in his time, and it was he who corresponded with William Dallimore of Kew after the hybridity of the Leyland cypresses had come to notice. For further details see the letter from E. H. M. Harris in Journ. Roy. For. Soc., Vol. 76 (1982), p. 132.

The remarks in the last paragraph on page 797 need qualification. The Leyland cypress is certainly of value as a free-growing screen or, except in very exposed localities, as a windbreak. It can also be used as a high hedge if the equipment and labour are available to keep it within bounds. But it is not suitable for the usual garden hedge, being far too vigorous for such a purpose. (It should incidentally be mentioned that the Leyland hedge in the Arboretum nursery at Kew has been removed.) With regard to the value of Leyland cypress as a fast-growing specimen, it should be added that ‘Leighton Green’ (clone 11) is far more suitable for this purpose than ‘Haggerston Grey’ (clone 2), which is what is commonly sold as Leyland cypress, at least in garden centres. See further below.

The volume number in the reference given at the top of page 798 was wrongly printed. It should be Vol. 58. A later article, with much interesting information, is: Alan Mitchell, ‘Growth Rate of Leyland Cypress’, The Garden (Journ. R.H.S.), Vol. 104 (1979), pp. 451-2.

cv. ‘Haggerston Grey’ (Clone 2). – Alan Mitchell, who chose the cultivarname for this clone, would be the first to admit that it is not apt. It is true that a spray seen close-to has a hint of grey in it, but at no time does the whole plant appear anything but green. Indeed, in shade of green there is really little difference between this and ‘Leighton Green’, but an obvious difference in the form of the foliage sprays, the lateral branchlets being decidedly irregular in ‘Haggerston Grey’, but flat and frond-like in ‘Leighton Green’. Also in the latter the ramifications are much stouter than in ‘Haggerston Grey’.

specimens: Haggerston Castle, Northumb., pl. 1892, the largest 92 × 834 ft (1984); Kyloe Wood, Northumb., cuttings from the Haggerston trees, pl. 1897, 90 × 814 ft and 95 × 734 ft (1977); National Pinetum, Bedgebury, Kent, in Avenue, 97 × 734 ft (1980) and in Valley, 102 × 7 ft (1982), both pl. 1935; Royal Horticultural Society’s Garden, Wisley, Surrey, pl. c. 1928, 98 × 12 ft (1981); Wakehurst Place, Sussex, in Pinetum, 105 × 712 ft and, above Pinetum, 102 × 534 ft (1979); Bicton, Devon, pl. 1916, 118 × 912 ft and 105 × 814 ft (1983); Inveraray, Argyll, 105 × 1112 ft at 3 ft (1982); Headfort, Co. Meath, Eire, pl. c. 1916, 104 × 912 ft (1980).

cv. ‘Leighton Green’ (Clone 11). – Although not difficult to propagate, this clone gives a lower percentage strike than ‘Haggerston Grey’, and is consequently scarcer in commerce. For hedging or screening there is no difference between them, but ‘Leighton Green’ makes the better specimen, being shapely even when young and developing a stout trunk more quickly. Apart from the difference in foliage already mentioned, another distinctive character of ‘Leighton Green’ is that it cones abundantly.

specimens: Leighton Hall, Powys, original tree pl. 1912, 98 × 1112 ft (1984); Royal Horticultural Society’s Garden, Wisley, Surrey, pl. c. 1928, 92 × 914 ft (1981); Wakehurst Place, Sussex, 75 × 834 ft (1979); Westonbirt, Glos., pl. 1933, 82 × 7 ft (1980); Borde Hill, Sussex, pl. 1935, two trees, 75 × 834 ft (1974) and 84 × 6 ft (1981); Powerscourt, Co. Wicklow, Eire, 72 × 8 ft (1980).

To show the rate of growth of a young tree: Chase Cottage, Haslemere, pl. c. 1963, 62 × 434 ft (1986).

Mention was made in the fourth paragraph on page 797 of clones 20 and 21. The original trees of these were seedlings of Cupressus macrocarpa and were raised at the Stapehill Nursery, about 1940. It was at one time doubted whether the trees were referable to × C. leylandii, on the grounds that no Nootka cypress grew in the vicinity to provide the pollen. But resin analysis by L. Gough has confirmed the hybrid parentage. Of the two clones ‘21’ is greatly superior to ‘20’ and in vigour rivals ‘Haggerston Grey’. Recent measurements of the original trees are: clone 20, 52 × 5 ft and, clone 21, 52 × 612 ft (1984).

The following clones of Leyland cypress have come into commerce since 1970:

cv. ‘Castlewellan Gold’. – Foliage golden when young, but usually becoming greenish yellow in winter. It is arranged as in ‘Haggerston Grey’. The history of this cultivar is that in the severe winter of 1962-3 snow broke off a coning branch from a large specimen of Cupressus macrocarpa ‘Lutea’, growing in the Forest Park at Castlewellan, Co. Down. Since a tree of a slightly golden form of Chamaecyparis nootkatensis grew nearby, John Keown sowed seed from the cones in the hope that some of the seedlings might be hybrids between the two. One proved to be so and was propagated. The clone was put into commerce in 1970 and soon became widely available. The original tree, put in its present position in 1965, measures 26 × 3 ft (1981).

cv. ‘Robinson’s Gold (‘Robinson’). – Foliage arranged as in ‘Leighton Green’, but bright yellow when young and perhaps rather brighter and more persistently coloured than in ‘Castlewellan’. It was found as a self-sown seedling among rhododendrons in Belvoir Park near Belfast, and put into commerce in 1975. The original tree measures 36 × 3 ft (1982).

There are also two clones of Leyland cypress with silvery foliage. ‘Harlequin’ arose as a sport on ‘Haggerston Grey’ at Weston Park and was distributed by the late Lord Bradford in 1975. Unfortunately, it is apt to make a forking leader. Better is ‘Silver Dust’, a sport of ‘Leighton Green’ raised in the USA, which keeps a straight stem and is vigorous.

† × C. notabilis A.F. Mitchell – A hybrid between Cupressus glabra and Chamaecyparis nootkatensis, raised in the Forestry Commission’s Genetics Nursery at Alice Holt, Hampshire. The seeds were collected in 1956 from a tree of C. glabra growing at Leighton Hall near to the Nootka cypress which forty-five years earlier had produced × C. leylandii (‘Leighton Green’ and ‘Naylor’s Blue’). Of the seedlings raised, two were abnormal and proved to be of hybrid origin. Planted at Alice Holt, one of the seedlings had attained 41 × 3 ft by 1980 and was accidentally felled a year later. The other measures 39 × 212 + 2 ft (1979). A propagation at Westonbirt, Gloucestershire, measures 40 × 2 ft (1980).

The Alice Holt cypress makes a narrow specimen of greyish aspect, with rather open sprays. See further in: A. F. Mitchell, Conifers in the British Isles (1972), p. 95 and fig. 71.

† × C. ovensii A.F. Mitchell – This hybrid was raised by Howard Ovens at Tan-y-Cae, Dyfed, from seeds (collected 1961) from a tree of Cupressus lusitanica growing at Westonbirt in the vicinity of Chamaecyparis nootkatensis. Several seedlings showed hybrid characters, and the description was made from one of three plants given to the Forestry Commission by the raiser. It is intermediate between the two parents and a vigorous grower. An example planted at Westonbirt measures 35 × 134 ft (1981).

These two hybrids were first described by A. F. Mitchell in Journ. R.H.S., Vol. 95, pp. 453-4 (1970).


'Haggerston Grey' (Clone 2)

Branchlets unevenly spaced, lying in two planes at right-angles and with side-shoots arranged irregularly round the axis; finest divisions also in more than one plane and circular in cross-section at the tips. This is the commonest of the clones in cultivation; in its system of branching it is nearer to the pollen parent Cupressus macrocarpa. The original tree at Haggerston Castle, planted in 1892, measured 72 × 5{3/4} ft in 1960 but has been outstripped by several of its offspring. Some of the tallest of these are: Bicton, Devon, 90 × 5{1/4} ft (1960); Wakehurst Place, Sussex, 77 × 5{3/4} ft (1964); R.H.S. Garden, Wisley, Surrey, 72 × 5{1/2} ft (1964); Inveraray Castle, Argyll, 74 × 6{3/4} ft (1960).

'Leighton Green' (Clone 11)

Leaves greener than in ‘Haggerston Grey’; branchlets and their subdivisions mainly in one plane and thus recalling the pollen parent, Chamaecyparis nootkatensis. This form is also in commerce but large specimens are rarer in gardens, perhaps because it is somewhat difficult to strike. The original tree at Leighton Hall measured 95 × 9{1/2} ft in 1968. Of its offspring some of the largest are: Wakehurst Place, Sussex, 63 × 6{1/2} ft (1964); R.H.S. Garden, Wisley, Surrey, 64 × 5{3/4} ft (1964); Westonbirt Arboretum, Glos., pl. 1933, 62 × 4{1/2} ft (1963).Other clones which have received names are: ‘Green Spire’ (Clone 1) and ‘Naylor’s Blue’ (Clone 10). The latter is only represented in cultivation by young plants, the parent having been blown down in 1955; it has the most glaucous foliage of the set and is the one that most closely resembles the Monterey cypress in general aspect.The Leyland cypress must be propagated by cuttings taken from side growths in March before growth commences or in late summer from half-ripened growths; these should be about 3 in. long and struck in sand with slight bottom-heat. When used for a windbreak, it is essential that the plants should be young and whippy, with a healthy and freely developed root-system. Heavy plants, or those which have had their anchorage roots forced downwards by constriction in a pot, will not be wind-firm.