Ash: Planting, Pruning, Care

Description and Botany

The Ash, in Latin Fraxinus, belongs to the Oleaceae family which includes jasmine, olive trees, as well as lilacs and osmanthus. The Fraxinus genus comprises around sixty species, three of which are particularly common in Europe. Among them, we find the Manna Ash (Fraxinus ornus), the Narrow-leaved Ash (Fraxinus angustifolia), the Common Ash (Fraxinus excelsior), and the Chinese Ash (Fraxinus chinensis).

Native to Europe, Asia Minor and North Africa, the ash is commonly found along riverbanks and in forests. Its upright and sturdy trunk is covered with bark, often silvery-grey, initially smooth, developing long fissures with age. It develops one or several trunks with diameters that can exceed 1 m.

Fraxinus excelsior. Botanical plate circa 1920

From a taproot, the ash forms an elegant tree with a conical to rounded, even spreading habit. The crown is airy, highly ramified with strong, slender branches. The Fraxinus excelsior ‘Pendula’, or weeping ash, stands out with its spreading parasol shape.

Ultimately, the ash reaches an average height of 5 to 20 m and up to 12 m in spread, sometimes more when mature, depending on species and growing conditions, with a growth rate ranging from fast to slow. Some ancient specimens can grow up to 40 m tall.

Sturdy branches support an airy and ample crown, finely ramified. Slender, glabrous twigs bear deciduous foliage. The ash’s foliage appears quite late in spring. It consists of pinnate leaves, each composed of 5 to 15 narrow, opposite leaflets. These leaves, lanceolate in shape, are easily recognisable by their finely dentate margins. They measure between 20 and 30 cm long and are glabrous and dark green on top, lighter underneath and slightly downy. Some, like the Fraxinus chinensis ‘Emma’s Gold’ display golden foliage, dazzling from spring to autumn. The Fraxinus angustifolia, or narrow-leaved ash, stands out with its finer and more elongated leaves compared to the common ash. As for the Fraxinus angustifolia ‘Variegata’, or variegated ash, it is distinguished by its white-edged leaflets, offering a striking visual contrast.

Fraxinus angustifolia ‘Raywood’, Fraxinus excelsior, silhouette (© Andreas Rockstein), and foliage. Right: Fraxinus excelsior ‘Pendula’ (© Leonora Enking)

In ash trees, the foliage displays a changing colour palette with the seasons, shifting from dark green in spring to flamboyant orange in autumn before falling.

Flowering typically occurs in spring, from March to May, often before the foliage appears. Oak flowering is usually not spectacular, however it is highly nectariferous, attracting many bees, bumblebees and butterflies. Their pollen can be allergenic. The ash is recognisable by its large, characteristic velvety black flower buds at the tips of stems. The flowers, devoid of petals, cluster in cream-yellow panicles, 10 to 20 cm long at the ends of annual shoots. The foliage disappears in spring beneath this fragrant, melliferous flowering, exuding a hawthorn-like scent. The Fraxinus ornus, or flowering ash, is an exception with its spectacular and massive flowering.

After pollination, greenish fruits called samaras appear in hanging clusters. These are achenes equipped with a wing, facilitating wind dispersal.

Ash trees play a vital role in biodiversity, providing habitat for numerous insects, birds and small mammals.

Flowering of a Fraxinus ornus, samaras of Fraxinus excelsior and autumn foliage of a Fraxinus pennsylvanica

Main species and varieties

Fraxinus excelsior - Ash

This is the common ash of our forests! With rapid growth, it becomes an elegant and airy tree. Perfect for a large garden or by a water feature.

• Flowering time May
• Height at maturity 30 m

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Fraxinus ornus - Manna Ash

This species stands out for its abundant and fragrant flowering in spring! This ash tree is well-suited to Mediterranean areas as it remarkably withstands drought and thrives in limestone soils.

• Flowering time June
• Height at maturity 7 m

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Fraxinus excelsior Pendula - Ash

Here is the weeping ash! It is distinguished by its spreading, parasol-shaped habit. Perfect as a standalone feature with its branches trailing down to the ground!

• Flowering time May
• Height at maturity 15 m

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Fraxinus chinensis Emmas Gold - Ash

A dwarf variety of Chinese ash with golden foliage, equally suitable for small gardens or containers.

• Flowering time May, June
• Height at maturity 5 m

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Fraxinus angustifolia - Ash

This ash tree is characterised by its very decorative fine foliage. It grows well in warm climates and tolerates temporarily dry soils.

• Flowering time May
• Height at maturity 15 m

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Fraxinus angustifolia Raywood - Ash

This variety is remarkable for the red hues its beautiful foliage takes on in autumn.

• Flowering time May
• Height at maturity 15 m

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Planting the Ash Tree

Where to Plant It?

The ash tree is very hardy down to -34°C (USDA zone 4) and adapts easily to various conditions, as it is undemanding. It tolerates all types of exposure, as long as it is not scorching. It grows readily in any good garden soil, even chalky, rich, deep and moist. Choose an open spot for it, sheltered from prevailing winds, in non-scorching sunlight. However, it does not particularly like the Mediterranean climate, which is too dry and hot, with the exception of Fraxinus ornus and the Southern Ash, which thrive in warm climates and adapt to dry, chalky soils, tolerating drought remarkably well. Generally, however, this riverside tree needs permanently moist soil, at least at depth, to grow well.

The ash tree is a large tree that can reach 20 m or more with age. Unless you choose a compact species, it should be planted in a garden large enough to accommodate it. Such a majestic tree requires a carefully chosen location, in deep soil and a very open position. If you are lucky enough to have a large garden, consider planting your ash tree as a standalone specimen or as part of an avenue. If you wish to incorporate it into a border, make sure you have enough space for it to develop freely. Its airy branches pleasantly filter the light in summer without creating too much shade. It will look splendid as a standalone by a pond, in a mixed hedge or a wooded border for the less bulky varieties.

Fraxinus excelsior in autumn, imposing and majestic (© manuel m.v.)

When to Plant It?

Ash trees are ideally planted in autumn, a favourable time for root establishment before winter, in any properly prepared and sufficiently deep soil. However, if you haven’t had time to plant it in autumn, you can do so until spring, avoiding frost periods. For container-grown specimens, planting can be done year-round, provided they are well watered during the first year. If you choose to plant in summer, regular watering is essential to prevent the tree from suffering from drought.

How to Plant It?

Choose a sunny and very open spot, shaded in hot climates. The ash tree is a large tree that requires ample space to develop properly. It is therefore particularly suited to large gardens where it can thrive without constraints. Allow at least 4 m between your ash tree and another tree. Be sure to respect planting distances so each plant has enough space to grow. Add organic matter at planting time, especially if your soil is poor.

• Dig a planting hole, two to three times the size of the root ball (approx. 1 to 1.40 m in diameter and 0.80 to 1 m deep)
• Spread a 30 cm layer of clay pebbles or gravel at the bottom of the hole
• Add one to three spadefuls of well-rotted compost
• Place the ash tree in the centre of the hole, ensuring the collar is not buried: the root ball should be level with the soil surface
• Backfill with soil and firm gently
• Stake with 1 to 3 supports
• Water thoroughly
• Spread a layer of mulch around the base to retain moisture and suppress weeds
• Water generously for the first few weeks to encourage establishment, especially during dry spells

Cultivation, care, pruning

The ash tree requires no maintenance, except for regular watering during the first three years, and in case of prolonged drought. The first year: maintain regular watering during the summer. Once well established, it can withstand temporary drought. In case of extreme heat, do not hesitate to increase water supply.

Mulch in summer to retain moisture at its base. Add compost in spring by lightly scratching the surface around the tree to encourage its growth.

Stake young plants to protect them from strong winds.

Pruning the ash tree

Pruning is only necessary if the tree becomes too large and the allocated space proves insufficient. It involves reducing the development of the crown. It is usually carried out in late winter, before the first leaves appear or after the bud burst period, avoiding frost periods. Limit pruning to small-diameter branches and, for mature trees, avoid severe pruning and cutting branches with a diameter exceeding 10 cm. Every three years or annually if needed, to rebalance the branches:

1. Remove dead or poorly oriented branches,
2. Shorten the longest branches to balance the tree’s habit
3. Thin out the centre of the crown

Fraxinus ornus

Diseases and potential pests

Ash trees are generally very resistant to diseases and pests. However, since 2012, they have been endangered by ash dieback, a formidable fungal disease that is decimating European ash trees and for which there is no treatment. Ash dieback causes necrosis at the collar, branches and can lead to the death of the tree. They may also be susceptible to honey fungus or root rot, a fungus that also leads to the death of the tree. As no treatment is effective against these deadly fungi, ensure perfect drainage when planting and avoid severe and repeated pruning, which leaves many wounds that serve as entry points for fungi and bacteria.

Pest insects (aphids, caterpillars…) may attack your tree, but they are not dangerous.

Propagation

The ash tree tends to self-seed very easily if conditions are favourable. To propagate it, you can collect the seeds in autumn, stratify them during winter (i.e., expose them to cold by placing them in the refrigerator), then sow them in spring. Sowing from fresh seeds is the simplest method of propagation. Propagating ash trees by grafting or cuttings remains a task for professionals.

By sowing

• Harvest the samaras in autumn, when they are fully ripe and detach easily from the tree
• Place them in cold conditions
• Soak the seeds in water for a day to encourage germination
• Fill a tray or pot with compost, then sow 1 or 2 seeds per pot
• Cover them with a thin layer of compost, then water lightly.
• Place the tray or pot outdoors, sheltered from harsh weather
• Let nature take its course during winter. The seedlings should begin to germinate in spring

Associations

With its elegant foliage and beautiful autumn colours, the ash tree is ideal as a standalone feature, in a row, or as a backdrop in a flower bed. Many plants thrive in the shade of large trees! The deciduous foliage of the ash tree provides welcome shade for plants that prefer partial or full shade. It will host lush ferns, Hostas, and the delicate, fresh flowering of Solomon’s Seals. Hydrangeas will also appreciate the shade provided by the ash tree’s foliage. An Acer campestre will also make a fine companion for creating a dazzling natural autumn display. It pairs well with the Cornelian cherry, as well as other spring-flowering bushes like Lilacs or Syringa.

Consider also creating vibrant, colourful ground cover by planting a variety of small spring bulbs beneath your ash tree; daffodils, tulips, and other spring bulbs can enjoy the sunlight before the ash tree develops its foliage. Some shade-loving perennials will take over for the summer, such as creeping bugleweed, Geranium macrorrhizum, and Pachysandra terminalis, forming a resilient flowering tapetum at its base, resistant to tree roots.

Common ash, Geranium macrorrhizum ‘Olympos’, hostas, tulips, and field maple

Did you know?

Particularly hard and dense, ash wood is used in cabinet-making and carpentry, especially for crafting tool handles. The Manna Ash, Flowering Ash (Fraxinus ornus), offers another fascinating asset: its manna, a sweet and syrupy sap harvested after incising the bark. Once widely used by apothecaries, manna is still valued in herbal medicine for its purgative and diuretic properties.