<em>Juniperus</em>, junipers: planting, pruning and care

Description and botany

Juniperus belong to family Cupressaceae along with cypresses (Cupressus), false cypresses (Chamaecyparis), Thuja and Calocedrus. Nearly 70 species make up genus if interspecific hybrids found in the wild are excluded. Like cypresses, junipers are distributed across Old and New Worlds while thujas and false cypresses occur only in North America and the Far East. Genus shows great resistance to cold and drought, like pines which often share same open habitat.

These massive trees, reaching up to 10 m, or erect or spreading bushes, have slow growth and great longevity.

Juniperus communis – botanical illustration

Evergreen foliage occurs in two distinct forms, short needles, sometimes sharp, arranged in threes on the twigs as in common juniper (Juniperus communis), or opposite scales paired and applied to the twig as in cypresses. However, some species bear both leaf types on the same plant, such as Juniperus chinensis, while others develop an adult form of scale-leaves after initially bearing needles. In all cases, foliage has aromatic glands that give it the distinctive smell of gin when crushed or in hot weather.

Male and female flowers generally appear on different plants. Sulphur-yellow aments form small catkins at twig tips. Female flowers take the form of miniature cones whose three scales remain fleshy and eventually fuse after fertilization to form a three-seeded spherical structure. These are called galbulus or false berries and have a bluish-black or reddish colour.

Heartwood (duramen) of juniper is also known for its strong scent, hardness and reddish hue, which contrasts with whiteness of the sapwood often visible on old specimens whose bark has been worn away by time.

Juniperus essential oil has many medicinal properties, notably antiseptic and diuretic, also used in homeopathy.

Juniper fruits

Main varieties of Juniperus

Varieties with spreading or creeping habit

Varieties with rounded habit

Variety with flared habit

Varieties with columnar habit

Juniperus communis var. hemisphera Hornibrookii

Prostrate juniper forming a slightly shaggy tapetum, with fine thorny branchlets, covered in dense foliage, grey-green above and silvery-blue beneath throughout the year. This extremely hardy, slow-growth conifer is a robust and vigorous groundcover, ideal for dressing a large slope, a wall or a rockery.

• Height at maturity 45 cm

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Juniperus rigida subsp. conferta Blue Pacific

Attractive tapetum of apple-green needles in spring, taking on a bluish tint under winter cold. Tolerant of soil salinity and sea spray, it thrives in full sun and sandy, even poor, soil. Slow-growth and very hardy in very free-draining soil.

• Height at maturity 30 cm

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Juniperus x pfitzeriana Old Gold

Spreading, supple branchlets of scale-like leaves golden-yellow at the base, bright yellow at the tips, gaining bronze tones in winter. Perfect for colonising a slope or filling a border in a small garden. Melliferous, it produces pretty small fruits, first red-purple then blue-black at ripeness, much appreciated by birds.

• Height at maturity 1 m

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Juniperus horizontalis Wiltonii

Elegant creeping juniper with a spreading, mat-forming, regular habit, gradually forming a superb evergreen groundcover. Foliage soft to the touch is grey-green with a blue tinge in summer, then acquires attractive purple highlights after cold.

• Height at maturity 20 cm

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Juniperus squamata Floreant

Rare conifer with compact, rounded, bushy habit whose striking foliage bears a beautiful blue-silver tone splashed with pale yellow to creamy-white year-round, sometimes tinged with mauve. More compact and brighter than variety 'Blue Star'. In a sheltered position away from direct sun, it remains attractive throughout the year.

• Height at maturity 45 cm

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Juniperus Blaauw

Narrow conical variety, very compact, its foliage yellowish-green to golden-yellow turning blue-green in winter. Slow-growth, perfect on a large slope or in a small garden. Well suited to topiary and can be grown as bonsai.

• Height at maturity 1,80 m

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Juniperus communis Arnold

Modest-sized columnar variety with soft green-grey-blue foliage, aromatic when crushed. This juniper is a slow-growth conifer but remarkably resilient, unaffected by cold winters or hot summers. Perfect in a mixed border, as a specimen, as a backdrop to a large rockery or even planted in groups of three.

• Height at maturity 2,50 m

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Juniperus squamata Loderi

Slender, modest-sized conifer in a more or less narrow or stocky pyramid shape, clad in dense, beautiful blue-green foliage, allowing multiple uses in gardens or in pots.

• Height at maturity 2,50 m

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Planting

Where to plant Juniperus?

Juniper favours full sun and well-drained soil as well as cold climates, even dry in summer, rocky or even shallow soils. Some species do well by the sea, such as beach juniper. Plant juniper at sufficient distance from bushes with shallow root systems such as camellia or from perennials, as it could compete directly for water and minerals.

Common junipers in particular possess a superficial root system that makes them vulnerable to strong winds. Choose a spot sheltered from prevailing winds, especially if bush has an erect habit. Creeping or spreading species present no risk of uprooting.

When to plant?

Plant Juniperus preferably in February–March or October–November.

How to plant?

This plant presents no difficulty in cold, even dry climates.

• Dip bucket in a bucket of water to thoroughly moisten it.
• Dig a hole three times wider than rootball and loosen soil around with tines of garden fork.
• Add a few handfuls of sand and gravel to ensure good drainage around roots. In heavy soil, opt for planting on a mound or within a rockery.
• Add well-rotted manure or compost if soil is sandy.
• Place plant in planting hole.
• Replace soil and tamp down lightly.
• Water.

Juniperus squamata ‘Chinese Silver’

Care and pruning

Water during the first summer following planting: soil must remain slightly moist to ensure good establishment.

Juniper is not very susceptible to diseases or pests. Needles that turn slightly yellow and then suddenly dry out can, however, indicate an attack by conifer aphids. Spray with an insecticidal treatment such as fern manure, pyrethrin or black soap and repeat the application after 8 to 10 days. If branches turn brown, cut them off and burn them immediately. Apply copper or a horsetail decoction; this is probably cryptogamic browning.

Pruning Juniperus

It can be done by removing one-third of the year’s shoots if you want to give a more compact habit or slow growth. Bear in mind that if you expose naked old wood, no regrowth will occur. This is an advantage for cloud training because you do not need to clean the trunks that make up the structure of the bush once the bush is formed. Limit yourself to reducing the year’s shoots to maintain the clouds. As in the art of bonsai, you can guide the branches by forming a spiralled shape with wire in order to instil an atypical form that will give charm and uniqueness to the specimen.

Multiplication

Simplest propagation is to separate layers from creeping forms that spread and often produce roots. Propagation by cuttings remains fairly delicate and sowing is possible only if your plant, female, produces fruit and is therefore near a male plant of same species. However, cultivar characters will not be reproduced.

Layering

• Start by loosening soil beneath a low branch.
• Remove leaves from area of branch to be buried and lightly scrape bark with fingernail.
• Sprinkle wound with plant hormone.
• Bury section of branch leaving tip protruding and hold in place with a metal staple.
• Rooting takes between 12 and 18 months.
• Then sever layer with pruning shear.
• Using spade, dig up rootball and plant promptly into a pot or directly in chosen spot. Discover our tutorial: How to take cuttings from conifers?

Uses and associations

Because of their slow growth, junipers are perfect candidates for filling large rockeries or structuring a garden, marking paths, forming borders like box, currently afflicted by many problems, or holly, which is more costly.

An autumn planting idea: Juniperus squamata ‘Blue Star’, Cornus sanguinea ‘Winter Beauty’ and Cotinus coggygria ‘Lilla’

Columnar forms can be planted singly or in threes for greater impact. Spreading or creeping forms make perfect groundcovers for large areas or hard-to-reach spots such as banks.

You can play with horizontal, vertical and rounded shapes of these small rockery conifers to create a graphic scene in nuanced tones of green — from pale to deep — grey, blue and even rust or purple in winter for cultivars that redden in cold.

They also do very well in pots and tolerate pruning extremely well, allowing many uses. The true graphic qualities of conifers naturally assert themselves in contemporary garden design, which favours aesthetics of shape, silhouette and texture over flowering displays.

Planting idea for a bank or large rockery: Juniperus communis ‘Compressa’ (or ‘Arnold’, ‘Gold Cone’ with golden foliage), Yucca gloriosa ‘Variegata’, Carex testacea ‘Prairie Fire’ (in very dry soil, replace with fescues, blue oat grass or Sporobulus) and Euphorbia myrsinites

Juniperus can be planted alongside mahonias, those bushes with holly-like foliage lit by a perfumed golden-yellow late-winter flowering, heathers whose flowering period can span all seasons, or windswept grasses whose character complements them well. You can also plant at their feet perennial plants for dry shade with low requirements such as periwinkles, Euphorbia amygdaloides purpurea, epimediums or Trachystemon orientalis.