Juniperus, 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 make up genus if interspecific hybrids encountered in wild are excluded. Like cypresses, junipers are distributed across Old and New Worlds while thujas and false cypresses occur only in North America and 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 bushy shrubs have slow growth and great longevity.

Juniperus communis – botanical illustration

Evergreen foliage appears in two distinct forms, short needles, prickly or not, arranged in threes on shoots as in common juniper (Juniperus communis), or scales opposite two by two applied against the twig as in cypresses. However some species bear both leaf types on same plant, such as Juniperus chinensis; others develop into adult form of scaly leaves after producing needles. In all cases, foliage has aromatic glands that give it gin-like scent when crushed or when warm.

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

Juniper heartwood (duramen) is also known for strong smell, hardness and reddish colour which contrasts with whiteness of sapwood often visible on old, weathered specimens.

Juniperus essential oil has many medicinal properties, notably antiseptic and diuretic, and is 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 somewhat hirsute tapetum, with thin thorny branches, covered in dense foliage, grey-green above and silvery-blue beneath, all year round. This extremely hardy and slow-growing conifer is a robust and vigorous groundcover, ideal for adorning a large bank, 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 hue under winter cold. Adapted to soil salinity and sea spray, it thrives in full sun and sandy, even poor, soil. Slow-growing and quite hardy in very well-drained 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 reflections in winter. Perfect for colonising a bank or for adding substance to a bed in a small garden. Melliferous, it produces pretty small fruits first red-purple then bluish-black when ripe, much appreciated by birds.

• Height at maturity 1 m

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Juniperus horizontalis Wiltonii

Elegant creeping Juniper with a spreading, carpeting and regular habit, forming over time a superb evergreen groundcover. Its foliage, soft to the touch, is a greyish-green tinged with blue in summer, then gains lovely purple highlights under the effect of cold.

• Height at maturity 20 cm

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Juniperus squamata Floreant

Rare conifer with a compact, rounded bushy habit, whose surprising foliage displays a magnificent silvery-blue tone splashed with pale yellow to creamy white all year round, sometimes tinged with mauve. More compact and luminous than variety 'Blue Star'. When sheltered from direct sun it remains attractive all year round.

• Height at maturity 45 cm

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Juniperus Blaauw

Narrow conical variety, very compact; its foliage yellowish-green to golden-yellow becomes bluish-green in winter. Slow-growing, it is perfect on a large bank or in a small garden. Well suited to topiary art 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 soft green-grey-blue foliage, aromatic when crushed. This Juniper is a slow-growing conifer yet remarkably resilient, insensitive to cold winters as well as hot summers. Perfect in a shrub border, as a specimen, in the background of 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 form, clad in dense foliage of a beautiful blue-green, allowing multiple 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 appreciates the full sun and well-drained soil as well as cold climates, even dry in summer, rocky or shallow. Some species are happy by the sea, such as the shore juniper. Plant juniper at sufficient distance from bushes with superficial rooting such as Camellia or from perennials as it could compete directly for water and minerals.

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

When to plant?

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

How to plant?

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

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

Juniperus squamata ‘Chinese Silver’

Care and pruning

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

Juniper is not very prone to diseases or pests. Needles that turn slightly yellow 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 to 10 days. If branches turn brown, cut them off and burn immediately. Apply copper or a horsetail decoction; it is probably cryptogamic browning.

Juniper pruning

It can be done by removing one-third of this year’s shoots if one wishes to give a more compact habit or delay growth. Bear in mind that if you expose old wood, no regrowth will occur. This is an advantage for cloud training, as you do not need to clean trunks that form bush structure once bush is established. Simply reduce this year’s shoots to maintain the clouds. As in bonsai art, you can train branches into a spiral using wire to instil an atypical shape that will bring charm and uniqueness to the specimen.

Multiplication

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

Layering

• Start by loosening the soil beneath a low branch.
• Remove leaves from the section of branch to be buried and lightly scrape the bark with your fingernail.
• Sprinkle the wound with plant hormone.
• Bury the portion of branch, leaving the tip exposed and secure it with a metal staple.
• Rooting takes between 12 and 18 months.
• Then sever the layer with pruning shears.
• With a spade, lift the root ball and plant it without delay in a pot or directly in the chosen spot. Discover our tutorial : How to take cuttings from conifers?

Uses and companion plants

Because of their slow growth, junipers are perfect candidates to fill large rockeries or to structure a garden, mark pathways, form borders like boxwood, which is currently suffering many ills, or holly, which is more costly.

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

Columnar forms can be planted singly or in threes to create more impact. Spreading or creeping forms make perfect groundcovers for large areas or hard-to-access zones such as slopes.

You can play with horizontal, vertical and rounded shapes of these small rock garden conifers to create a graphic scene in nuanced tones of greens, 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 very well, allowing many uses. The true graphic qualities of conifers naturally assert themselves in contemporary garden design, which favours aesthetics of form, silhouette and texture over the parade of flowering.

An idea for a slope 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 up by perfumed golden-yellow late-winter flowering, heathers whose flowering period can cover all seasons, or scruffy grasses with very complementary character. It is also possible to plant at their base undemanding dry-shade perennial plants such as periwinkles, Euphorbia amygdaloides purpurea, epimediums or Trachystemon orientalis.