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

Description and botany

Juniperus belong to family Cupressaceae alongside cypresses (Cupressus), false cypresses (Chamaecyparis), Thuja and Calocedrus. Nearly 70 species comprise genus if interspecific hybrids occurring naturally are excluded. Like cypresses, junipers are distributed across Old and New Worlds, whereas thujas and false cypresses occur only in North America and the Far East. Genus shows great resistance to cold and drought, much like pines that often share same open habitat.

These massive trees, reaching up to 10 m, or erect or spreading bushy shrubs display slow growth and great longevity.

Juniperus communis – botanical illustration

Evergreen foliage occurs in two clearly distinct forms, short needles, prickly or not, arranged in threes on the shoots as in common juniper (Juniperus communis), or opposite scales paired two by two applied against the shoot as in cypresses. However some species bear both leaf types on same plant, as in Juniperus chinensis, while others develop an adult form of scale leaves after bearing needles. In all cases, foliage bears aromatic glands that give it the distinctive gin-like smell when crushed or in hot weather.

Male and female flowers are usually borne on separate plants. Sulphur-yellow aments form small catkin-like clusters at shoot tips. Female flowers are miniature cones whose three scales remain fleshy and eventually fuse after fertilization to form a spherical structure with three seeds. They are called galbulus or false berries and have a bluish-black or reddish hue.

Juniper heartwood (duramen) is also known for its strong aroma, hardness and reddish colour that contrasts with whiteness of the sapwood often visible on old specimens with bark worn away by time.

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

Juniper fruits

Main Juniperus varieties

Variétés à port étalé ou rampant

Variétés à port arrondi

Variété à port évasé

Variétés à port colonnaire

Juniperus communis var. hemisphera Hornibrookii

Prostrate juniper forming a slightly shaggy tapetum, with fine thorny twigs, covered by dense foliage, grey-green above and silvery-blue beneath throughout the year. This extremely hardy and slow-growing 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

Beautiful tapetum of apple-green needles in spring that takes on a bluish tinge under winter cold. Suited to soil salinity and coastal spray, it prefers full sun and sandy, even poor, soil. Slow-growing and very hardy in very free-draining soil.

• Height at maturity 30 cm

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Juniperus x pfitzeriana Old Gold

Spreading, supple branches of scaly leaves golden-yellow at the base and bright yellow at the tips, taking on bronze hues in winter. Perfect for colonising a slope or for filling out a bed in a small garden. Melliferous, it produces pretty small fruits that are initially red-purple then blackish-blue 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 and regular habit, which over time creates a superb evergreen groundcover. Its foliage, soft to the touch, is grey-green tinged with blue in summer, then develops lovely purple highlights in cold weather.

• Height at maturity 20 cm

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Juniperus squamata Floreant

Rare conifer with a compact, rounded, bushy habit whose striking foliage bears a magnificent silvery-blue hue splashed with pale yellow to creamy white year-round, sometimes tinged with mauve. More compact and brighter than variety 'Blue Star'. Sheltered 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 bluish-green in winter. Slow-growing, it is perfect on a large slope or in a small garden. Well suited to topiary and can be trained as a bonsai.

• Height at maturity 1,80 m

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Juniperus communis Arnold

Modest-sized columnar variety with softly grey-blue-green foliage, aromatic when crushed. This juniper is a slow-growing but remarkably resilient conifer, unaffected by cold winters or hot summers. Perfect in a bed, as a solitary 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 conifer of modest size in a more or less narrow or stocky pyramid shape, clad in dense, lovely blue-green foliage, allowing many uses in the garden as well as 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, stony or even shallow soils. Some species do well by the sea, such as beach juniper. Plant juniper at a sufficient distance from bushes with a superficial root system such as Camellia or from perennials as it could directly compete 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?

Preferably plant Juniperus in February–March or October–November.

How to plant?

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

• Immerse bucket in a bucket of water to thoroughly moisten it.
• Dig a hole three times wider than the 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 firm lightly.
• Water.

Juniperus squamata ‘Chinese Silver’

Care and pruning

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

Juniper is not very prone to pests or diseases. Slightly yellowing needles that then suddenly dry out may, however, indicate an attack by conifer aphids. Spray an insecticidal product such as fern manure, pyrethrin or black soap and repeat application after 8–10 days. If shoots turn brown, cut them off and burn them immediately. Apply copper or a horsetail decoction; this is most likely cryptogamic browning.

Pruning of Juniperus

Pruning can be done by removing one-third of this year’s shoots if a more compact habit is desired or to delay growth. Bear in mind that if you leave old wood naked, no regrowth will occur. This is an advantage for cloud pruning as you do not need to clean trunks that form the structure of the bush once it is established. Simply reduce the year’s shoots to maintain the clouds. As in the art of bonsai, you can direct branches by forming a spiralled shape with wire to instil an unusual form that will add charm and uniqueness to the specimen.

Multiplication

The simplest propagation method involves separating layers on creeping forms that spread and often produce roots. Propagation by cuttings is fairly tricky and sowing is only possible if your plant is female, produces fruit and is therefore close to a male plant of the same species. However, cultivar characteristics will not be reproduced.

Layering

• Begin by loosening the soil beneath a low shoot.
• Remove leaves from the section of shoot to be buried and lightly scrape the bark with a fingernail.
• Sprinkle the wound with plant hormone.
• Bury the portion of shoot, leaving the tip exposed and secure it with a metal staple.
• Rooting takes between 12 and 18 months.
• Then sever the layer with a pruning shear.
• Using a spade, lift the rootball and plant it promptly in a pot or directly in the chosen spot. Discover our tutorial : How to propagate conifers?

Uses and associations

Because of their slow growth, junipers are perfect candidates to fill large rockeries or to structure a garden, mark paths, form borders like box, currently suffering from many problems, or holly, more expensive.

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

Columnar forms can be planted singly or in groups of three to create more impact. Spreading or creeping forms make excellent groundcover to cover large areas or difficult-to-access zones such as embankments.

You can play with horizontal, vertical and rounded shapes of these small rockery conifers to create a graphic scene with subtle shades of green ranging from light to dark, grey, blue, even rust or purple in winter for cultivars that redden in the cold.

They also grow very well in pots and tolerate pruning well, which allows many uses. True graphic qualities of conifers naturally assert themselves in the design of a contemporary garden, which favours the aesthetics of shape, silhouette and texture over the display of flowers.

A planting idea for an embankment 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 grasses with tousled habit that complement them well. You can also plant dry-shade perennial plants at their feet with low requirements such as periwinkles, Euphorbia amygdaloides purpurea, epimediums or Trachystemon orientalis.