Cedar: planting, pruning and care

Description and botany

Cedars belong to the Pinaceae family, just like Pines and Firs. Although several other quite different resinous trees such as Chamaecyparis and Thuja are also called cedars, the genus Cedrus consists of only 2 to 4 species depending on classifications, found from Morocco to the foothills of the Himalayas in very localised areas. The Atlas cedar or Cedrus atlantica (syn. Cedrus libani subsp. atlantica) indicates that this species is the closest to the Atlantic. It grows in the Atlas Mountains, in Algeria and Morocco, between 1,500 and 2,500 m altitude, particularly on the watered northern and western slopes. The drought of recent years and especially rampant deforestation have placed this essential oil in danger of extinction. It is, in fact, a species discovered very late, around 1838, when France created the Forest Service in Algeria, whereas the Himalayan cedar (Cedrus deodara) was known and introduced to France for the first time in the 16^th century, although its widespread distribution only began in the mid-19^th century. The Cedar of Lebanon, introduced to France by Bernard Jussieu around 1734, quickly became popular as an ornamental tree, and it is not uncommon to encounter specimens with a circumference of 9 to 10 m in Great Britain and France, with heights exceeding 30 m. Native to the heights near the eastern Mediterranean coast (Turkey, Syria, and Lebanon), it is unfortunately endangered in its natural range, where it has become rarer than in all our parks and avenues!

The Himalayan cedar grows on the foothills of the famous mountain range between 1,500 and 3,300 m altitude, from Afghanistan, Pakistan, India, Kashmir, to Nepal. This large temperate forest tree, which depending on altitude is sometimes associated with resinous trees, sometimes with leafy ones, appreciates mild and humid climates and can sometimes be sensitive to spring frosts in our regions. It can reach up to 75 m in its natural range!

Cedrus deodara – botanical illustration

The name Kedros was used by the ancient Greeks to refer to both juniper and cedar. In the 18th century, this tree was successively classified in the genera Larix (larch), Juniperus (juniper), and Pinus (pine) by Carl von Linné before being established as a separate genus, Cedrus, in 1841.

These trees reach venerable ages of several centuries or even several thousand years, as evidenced by some specimens of the Cedar of Lebanon. In Europe, their heights rarely exceed 20 to 30 m. The stiff ascending branches of young Atlas and Lebanon cedars spread with age while the leading shoot bends, resulting in a very characteristic tabular habit. The tree’s height growth can sometimes be alarming, but it takes about thirty years for its silhouette to flatten out, and it’s best to avoid cutting the leading shoot. Cedrus libani ‘Nana’ benefits from very slow growth and a prostrate habit suitable for rock gardens, while the Turkish subspecies stenocoma is almost columnar.

Cedrus deodara retains a pyramidal habit with slightly pendulous branches and has more flexible and longer needles than other cedars, measuring from 3.5 to 5 cm. The bluish colour of the needles is typical of Cedrus atlantica forma glauca, also called the blue cedar. This form, very popular in our gardens, has a slightly more flexible habit than the type species with dark green needles. The Cedar of Lebanon has intermediate-length needles measuring 3 to 3.5 cm, followed by the Atlas cedar with a length between 2 and 2.6 cm, and then the Cyprus cedar with an average of 1.2 cm, as its Latin name brevifolia suggests, meaning “short-leaved”. The young shoots are downy, except for Cedrus libani, which has almost glabrous shoots. The bark, initially grey and smooth in young specimens, becomes more fissured and scaly over the years.

The evergreen leaves are arranged in rosettes of 10 to 60 needles on dwarf shoots and singly along long shoots. They persist for 3 to 6 years before falling. The tree produces resin, which gives off that pleasant smell that also permeates the wood, renowned for being very hard and rot-resistant. It is used to perfume and repel insects in wardrobes.

The cedar begins to bear fruit around the age of 40. The male aments form small yellowish clubs 3 to 6 cm long at the ends of branches in early summer, releasing their pollen in autumn. The female conelets appear at the top of the tree in autumn and mature over 2 to 3 years.

The cedar cones, green-purple then brown, have a fairly smooth egg shape and stand erect on the branch. They measure less than 8 cm long in Cedrus atlantica, 10 cm with a rounded top in Cedrus deodara, and 9 to 15 cm with a flat or concave top in Cedrus libani, which thus has the largest cones. At ripeness, the thin scales open and disintegrate in the wind, releasing the brown triangular seeds measuring 5 to 10 mm.

The fabulous blue cedar: male aments, bluish needles, and female cone

Cedar wood, prized for its resistance, is used in shipbuilding, timber framing, cabinetmaking, as well as in crafts and as firewood. It was used to build the doors of Solomon’s Temple and holds strong symbolism in the three monotheistic religions. The essential oil extracted from the wood and needles and its resin have antiseptic, diuretic, and sudorific medicinal properties.

There are remarkable forest stands of Atlas cedar in the Luberon, Ventoux, Aigoual, and Lauragais regions.

The main varieties of Cedar

The length of the needles as well as the shape and size of the cones are the main criteria for identifying the 3 recognised species.

Large-growing varieties

Cedrus libani subsp. atlantica Glauca - Blue Atlas Cedar

A majestic conifer with a lofty, broad and pyramidal habit, featuring splendid bright blue needle foliage in spring. It takes on beautiful silvery-grey hues in summer. Over the years, this tree becomes an imposing specimen with extraordinary aesthetics, absolutely stunning in a large garden!

• Height at maturity 20 m

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Cedrus libani - Lebanese Cedar

Its spreading branches, arranged almost horizontally, give the Cedar of Lebanon its characteristic tiered and tabular silhouette, while its very dark green foliage allows it to stand out admirably in the landscape. The hardiest of cedars, to be planted in full sun, in ordinary but deep, well-drained soil.

• Height at maturity 50 m

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Low-height variety

Cedrus libani atlantica Pendula - Lebanese Cedar

With its extremely weeping habit and slow growth, this magnificent conifer forms over many years a mass 4m high and 6m wide, cascading down in dark green with silvery tones. An exceptional specimen to plant as a standalone or by a water feature.

• Height at maturity 4 m

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Planting a cedar tree

Where to plant?

Cedars are conifers resistant to urban pollution, though the Lebanon cedar is slightly less resilient, and fairly hardy, tolerating frosts down to -15°C. However, we observe an increasing order of hardiness as follows: deodara, atlantica, then libani. They thrive in zones 6 to 9, except for the deodara, which is limited to zones 7 to 9 (minimum -16°C). The latter is also more sensitive to late frosts.
Cedars prefer fertile, deep and moist soils, but they can adapt to much less favourable conditions as long as the soil is well-draining, and tolerate summer drought once established.
Choose a very sunny spot, open and unshaded, but sheltered from wind tunnels, and most importantly, anticipate the future growth of this tree! It dislikes being moved as its root system needs to anchor firmly in the soil to withstand drought and wind.

When to plant?

Plant preferably from September to November or February to June, especially in slightly heavy soils.

How to plant?

This plant is easy to cultivate if young plants are used. Choose a well-branched specimen with a balanced silhouette and a leading shoot to grow into a tall tree.

• Soak the root balls thoroughly before planting by immersing the pot in a bucket of water while digging the hole.
• Dig a deep hole, 3 times wider than the root ball, and aerate the surrounding soil with a fork. Avoid heavy, waterlogged soils in winter.
• Add a few handfuls of sand and gravel to ensure good drainage around the roots.
• Incorporate well-rotted manure or compost if the soil is poor.
• Place the plant in the planting hole with 2 or 3 stakes driven deep around the root ball.
• Backfill the soil and firm gently.
• If the young plant is already large, secure the trunk to the stakes with flexible ties.
• Create a watering basin and water generously.

A few cedars: Cedrus libani, Cedrus deodara, Cedrus atlantica and Cedrus libani atlantica Pendula

Pruning and maintenance

Pruning Cedar Trees

For cedars intended to grow into large specimens, simply gradually prune the lower branches flush with the trunk up to the desired height, as the lower branches – which can eventually become obstructive – don’t always shed naturally. Then remove dead wood and small shoots growing inside the canopy to clear the main branches and create “windows” to reduce wind resistance. The intervention of a tree surgeon is often necessary for large specimens to lighten the branches and prevent breakage. Remove dominated branches (the most horizontal ones) that take time to shed naturally. If branches are torn off during a storm, cedar wood tolerates heavy pruning and heals well. Pruning can be done year-round except during the bud burst period in spring.

Maintenance

• Water generously in the first few years and during prolonged drought, and hoe the soil or mulch to retain moisture.
• Optionally apply a “conifer” fertiliser in April if you wish to accelerate growth, which is typically only 3-4 m over 10 years for standard species, less for golden or weeping forms.
• Protect young Himalayan cedars with winter fleece in case of late frosts.

Potential Pests and Diseases

Cedars are rarely diseased but may occasionally suffer an attack from processionary caterpillars, as with pine trees. This pest is identified by large silky nests in the branches and columns of blackish, villous caterpillars. These butterfly larvae have the drawback, in addition to feeding on the tree’s needles, of expelling urticating hairs at the slightest disturbance.

To learn more, visit this guide: “Pine Processionary Caterpillar: Risks and Control Methods”

Black aphids and red spider mites may attack the needles. Deter them with a jet of water.

Propagation

The most common method of propagation is sowing in late autumn or spring, for botanical species and certain blue-leaved varieties. Grafting is practised for cultivars to preserve their character, but this is a task for specialists. The rootstock can be any of the 3 species, regardless of the nature of the scion, except for Cedrus libani ‘Glauca’, which requires Cedrus deodara as the rootstock.

Sowing

The germination rate is only around 30%. Seeds can be stored for a maximum of 2 years in a dark, dry place.

1. Collect the seeds when the cones begin to disintegrate on the tree, usually after 2 or 3 years of ripening.
2. Stratify the seeds by sowing them in late autumn in a pot covered with fine mesh, or refrigerate them for 1 to 2 months before spring sowing.
3. Keep only the strongest young plants.
4. Do not wait too long to transplant the young plants, as cedars dislike root disturbance.

Uses and Combinations

The cedar forms a stunning standalone specimen that spreads both in height and width over 5 to 10 m. Allow for a large open space, as a single large conifer is sufficient in a garden under 2000 m². The blue cedar creates a spectacular scene in autumn when placed in front of leafy trees such as maples or liquidambars. Its silhouette and longevity also make it a highly valuable bonsai.

Cedrus deodara Aurea, or golden Himalayan cedar, is one of the most widely planted due to its compact size (3 m in diameter and 8 to 10 m in height at 20-25 years) and the brightness of its distinctly yellow shoots, which turn greenish-yellow in summer. ‘Kelly Gold’, with its slightly narrower and more compact habit, will tolerate sun exposure better.

From left to right: Cedrus libani and Cedrus deodara

Be cautious with the weeping Atlas cedar, which can exceed 15 m in diameter despite its very slow growth. However, you can train its long branches along sturdy supports and control its spread with careful pruning. It makes an exceptional specimen, best planted alone or even, why not, beside a water feature that will reflect its image in a grand romantic gesture. In this setting, it will serve the same ornamental role as a weeping willow, while being far less demanding regarding soil conditions. Indeed, the Atlas cedar is not only very hardy but also capable of thriving in poor, rocky, and dry summer soils.

In a very large garden, you could also plant several specimens along a driveway leading to a grand residence. This approach will take on an entirely new dimension, exuding both elegance and romance. Space the trees sufficiently, 7 to 10 m apart, to avoid overcrowding as they mature.

The striking graphic qualities of dwarf cedars (Cedrus deodara ‘Golden Horizon’, ‘Feeling Blue’) or those trained as bonsai naturally lend themselves to contemporary garden design, which favours the aesthetics of shapes, silhouettes, and textures over the fleeting dance of flowering. These enduring, reassuringly permanent plants provide lasting structure to borders, define pathways, and edge terraces, easily replacing the strong presence of clipped boxwood or holly. The key is to play with volumes and colours.

Create bold contrasts by pairing blue or golden cedars with vibrant spring and autumn-flowering mollis azaleas.

You can insert lungworts or bulbs such as Naples cyclamen, wood hyacinths, or squills at the base of large cedars to create delightful surprises. Don’t hesitate to plant a perennial border in the foreground to enliven the view from the house.

Did you know?

Although closer to home, the Atlas cedar was only discovered around 1830, whereas the Lebanon cedar was described and introduced under Francis I by Pierre Belon between 1546 and 1549, during a diplomatic mission to Suleiman.