Jooni

An exemplary photo of a Common Ash bonsai

Common Ash

1 Species

Species

Fraxinus excelsior

The Common Ash (Fraxinus excelsior), also called European ash, is a fast-growing deciduous tree native to Europe, with grey bark, pinnate leaves and conspicuous black winter buds. A Common Ash bonsai is an outdoor tree all year round that needs a cold winter dormancy and should never be kept indoors.

It is hardy, vigorous and forgiving, which makes it a reasonable choice for beginners. Its large compound leaves and long internodes make fine ramification slow to achieve, so it is best grown as a larger bonsai in informal upright, broom or forest styles.

At a glance Fraxinus excelsior

Difficulty
Beginner
Placement
Outdoors
Light
Full sun
Watering
High
Min. temperature
-10°C (14°F)
Foliage
Deciduous

Fertilizing

Feed every four weeks from spring, once the new leaves have opened, until late summer, using a balanced fertilizer. Ash is vigorous and does not need heavy feeding; too much nitrogen only lengthens the internodes and enlarges the leaves.

  • Use solid organic fertilizer or a liquid fertilizer at the dose on the label.
  • Stop feeding in autumn so the tree can harden off before winter.

Placement

Keep your Common Ash bonsai outdoors year-round in full sun, where it develops shorter internodes and smaller leaves. Good air circulation helps prevent fungal problems.

The tree itself is very frost hardy, but roots in a shallow pot are more exposed than in the ground. When temperatures fall below about -10°C (14°F), protect the pot by sinking it into the ground, mulching it or moving it to an unheated shed or cold frame.

Pruning

Ash has opposite buds and a strong leading bud on each shoot, so it tends to grow long, straight branches. During the growing season, let shoots extend and then cut them back to one or two pairs of leaves, which forces buds lower down and builds ramification.

  • Do structural pruning in late winter or early spring, just before the buds open.
  • Partial leaf pruning in early summer can reduce leaf size on a healthy tree.
  • Wire in late winter before bud break, check often and remove wire before it bites into the fast-thickening branches.

Repotting

Repot young trees every 2 years and older trees every 3-5 years, in early spring when the buds begin to swell. Ash tolerates root pruning well, so you can remove up to about a third of the root mass of a healthy tree.

Use a well-draining bonsai mix, for example akadama, pumice and lava rock with a little pine bark. Ash is not fussy about pH and grows well in slightly acidic to slightly alkaline soil (pH 6-7.5).

Watering

Ash likes moisture and should never dry out completely in the growing season, as this causes leaf scorch and die-back. Water thoroughly as soon as the top layer of soil feels slightly dry, which may be daily in summer.

Avoid permanently soggy soil, which leads to root rot. In winter the leafless tree needs much less water, but keep the soil slightly moist.

Seasonal care

  • Spring: Repot and do structural pruning as the buds swell, then start feeding once the new leaves have opened. Watch for aphids on the soft new shoots.
  • Summer: Water often, even daily, and cut long shoots back to one or two pairs of leaves. Partial leaf pruning in early summer can reduce leaf size.
  • Autumn: Stop feeding and let the tree harden off; the leaves often drop early and with little autumn color. This is a good time to see and plan the branch structure.
  • Winter: Leave the tree outdoors for its dormancy and protect the pot when temperatures fall below -10°C (14°F). Keep the soil slightly moist and wire if needed before the buds open.

Common problems

The Common Ash is robust, but watch out for these problems.

  • Ash dieback: A fungal disease (Hymenoscyphus fraxineus) causing wilting leaves, dark diamond-shaped lesions on the bark and dying shoots. Cut out affected branches well into healthy wood, rake up fallen leaves and do not collect material from infected trees.
  • Long internodes and large leaves: Caused by too much shade, too much nitrogen or letting shoots run unchecked. Give full sun, feed moderately and cut shoots back to one or two pairs of leaves.
  • Leaf scorch and early leaf drop: Usually a sign that the soil dried out in hot weather. Water as soon as the surface is slightly dry and shade the pot during heat waves.
  • Aphids and scale insects: They suck sap from young shoots and leaves. Rinse off aphids with water and treat heavier infestations, or scale on the bark, with horticultural oil or insecticidal soap.