The junipers are deservedly gaining in popularity as garden plants and a much wider range is being introduced to the British Isles from other parts of the world to give the gardener an even better choice. Most species are very hardy and grow successfully in even the poorest of soils, whether acid or alkaline. There is such a wide range of colours, shapes and forms in this genus that one would make quite an attractive garden growing only junipers. Unfortunately only a limited selection can be made here.
Juniperus chinensis aurea is an excellent garden variety of the Chinese juniper. Although very slow growing initially, even to the point of finding it difficult to assert a leading shoot, it eventually makes a beautiful golden columnar-shaped specimen. What adds to the attraction is that the plant usually carries both adult and juvenile foliage giving it more variety in shade and texture. Perhaps growing only 3 ft. in ten years, it eventually may get as high as 30 ft.
One of the bluest junipers is J. c. pyramidalis which has a broadly conical habit and very prickly foliage. After ten years it will grow to 5 or 6 ft. and with age broaden and grow as high as 15 to 20 ft. Like many junipers it is better planted in an open position.
J. communis is one of the three conifers native to the British Isles. It has given us several useful garden forms, some upright, some prostrate. J. C. compressa is quite a unique variety with its perfectly symmetrical outline, its slowness of growth and its usefulness as a sink or trough garden conifer. It is a must for the rock garden also and looks particularly attractive planted in groups of three or more. Bright green in summer, it turns a bluish-green hue in winter. Perhaps at ten years reaching 12 to 18 in., it will be very rare to see a specimen over 3 to 4 ft.
J. c. depressa aurea is a golden prostrate form of great merit. It needs to be planted in an open position for best effect where its butter-yellow shoots in spring provide a beautiful effect. The foliage turns a bronzy hue in winter with the silver undersides of the leaves more prominent. One should expect a spread of 3 to 4 ft. in ten years and increasing after many more years to 10 to 12 ft.
J. c. hibernica, known as the Irish juniper, is useful where an upright conifer is required. This will eventually reach 18 to 20 ft. One of the best ground-cover junipers is J. c. repanda which makes a very vigorous dark green carpet which turns a greeny brown during the winter months. It has a similar rate of growth to depressa aurea.
J. horizon talis is commonly known as the creeping juniper and this name describes the habit of the species and its many varieties admirably. The species originates from North America where it and many varieties are grown widely for garden and landscape use.
The most popular form in Europe is J. h. glauca, a carpet-forming plant which roots from runners as it spreads across the ground. The foliage is bright steel blue in summer, grey green in winter. To increase the density the runners can be pruned back occasionally. Similar forms occur in douglasii, Bar Harbor and wiltonii. All will spread quite rapidly covering a diameter of 6 to 8 ft. in ten years and ultimately considerably more. New and distinct varieties are likely to be introduced to Europe from the United States but one which is available and probably the best for ground cover is J. h. plumosa, the Andorra juniper. Where varieties so far mentioned grow flat to the ground, this will reach If to 2 ft. in height providing a more effective smother to weeds. The foliage is softer and more feathery, the colour grey green turning a purple hue in winter. All J. horizontalis varieties are extremely hardy.
J. media includes some forms which may be listed under J. chinensis in books and catalogues. I think it is now generally accepted that they should belong in this grouping but the main thing from a gardener’s point of view is that all those mentioned here are excellent garden plants. J. m. hetzii is an extremely vigorous semi-prostrate variety. It has grey-green foliage the year through and can be used as a specimen plant, as a low hedge or as a ground-cover plant. To increase density pruning will be necessary but in no way detrimental to the plant. Tolerant of alkaline soils it will grow better in sun than shade. An all-purpose plant but give it room as by the time it is ten years old it will be 5 ft. high and 6 ft across, eventually spreading 12 ft. across by 8 to loft, in height. But also remember the pruning! Old Gold is in my opinion better in a smaller garden than J. m. pfitzeriana aurea.lt is much more compact in growth with a better, year-round golden colour. It will probably reach 2f to 3 ft. in ten years and spread 3 to 4 ft. against 3 ft. by 6 ft. for pfitzeriana aurea over the same period. Ultimately it may be 6 ft. high and 8 ft. across whilst pfitzeriana aurea might be 6 ft. high but 12 ft. or more in diameter. The green J. m. pfitzeriana is even more vigorous although like the garden form an excellent ground coverer. It is not for the small garden I suspect but hardy and adaptable succeeding well on chalk. Forms may vary from nearly prostrate to maybe loft, or more in height. The growth rate for pfitzeriana aurea applies but perhaps add 30 per cent. On both the ten-year and ultimate figures. J. sabina, the savin juniper, has given us many useful garden forms, mostly prostrate or semi-prostrate in habit. All have the pungent odour of the species when the foliage is crushed. The variety Blue Danube doesn’t really live up to its name as far as the blue is concerned but otherwise it is a very attractive garden plant, especially when used as a ground coverer. It will grow quite rapidly — in ten years about 3 ft. high and a spread of 6 to 8 ft., eventually 4 ft. high and 15 ft. across.
Almost the most popular prostrate variety of juniper is J. s. tamariscifolia which makes a beautiful specimen with age, building itself up in layers and covering a wide area. It is particularly attractive on a large rock garden or a bank where it moulds itself into the contours. The foliage colour is grey blue. After ten years it should grow about 1 ft. high but spreading 3 ft. However, as branches root along the ground, it can spread to 15 ft. or more in time and attain a height of 18 in. to 2 ft.
Of recent introduction to Europe are forms of J. scopulorum, the Rocky Mountain juniper, which are very popular in the United States. They are mostly medium growers with conical or pyramidal habits. They would appear to be tolerant of most soil conditions but need to be placed in exposed or sunny situations for best results. Perhaps the best known is Skyrocket, a name which speaks for itself. This makes an extremely narrow column of blue grey, growing 7 to 8 ft. in ten years and ultimately 20 to 25 ft. It is extremely useful as an accent plant as are some of the others such as Blue Heaven of similar growth rate but a more pyramidal habit. The colour of the foliage is an intense silvery blue in summer but dulls somewhat in winter. Springbank has bright silver-grey foliage but much thinner branches. It is somewhat slower in growth than the previous two mentioned.
J. squamata has given us a few good forms and Blue Star, although only of recent introduction, promises to be one of the best for the smaller garden. It is slow growing with dense steel blue foliage and a bushy habit. It is likely in ten years to be 12 to 18 in. in height with a similar spread, and (taking a guess at it) probably at maturity 2 to 3 ft. high by 3 to 4 ft. across. Probably the best-known form of the species is meyeri which was introduced from China early this century and is now grown all over the world. It is also steel blue in colour, making a somewhat irregular bush with nodding leading shoots which are typical of the species. It needs an open position and some trimming may be necessary from time to time — these precautions will help to prevent the browning of the foliage sometimes seen on older specimens.
J. virginiana is native to the eastern United States and Canada and there is known as the pencil cedar as the species generally has a narrowly columnar shape. It and the garden forms it has produced are all very hardy and amenable to most soil conditions. The variety burkii is known in the British Isles but not used widely which is a pity. It is a useful plant with a broadly conical habit, the dense foliage blue grey in summer, turning a purplish hue in winter. Growing 8 to loft. High in ten years, it will ultimately reach 20 to 25 ft.
One of the best of all the semi-prostrate junipers is J. v. Grey Owl which has thin spreading branches of grey blue and is extremely vigorous in growth. A useful ground-cover plant it will, however, eventually need more space than is available in some gardens. After- ten years it will probably reach 12 to 18 in. in height and spread 8 to 10 ft. and after several more years 3 to 4 ft. in height with a spread of 15 to 18 ft.