Tasmanian blue gum

How to recognise it

Habit

In Australia a giant of 40–60 m, in southern Europe often 30–40 m, with a straight trunk. In Belgium, in a pot or as a foliage plant for one season, usually 1–3 m.

Leaf

Two kinds. Juvenile leaves: opposite, stalkless, oval, 7–15 cm, with a blue-grey bloom, on square stems. Adult leaves: alternate, stalked, long and sickle-shaped, 15–30 cm, glossy dark green and hanging. They smell of eucalyptus when crushed.

Flower

Large, creamy white flowers made up of a brush of many stamens, usually one per leaf axil. The bud has a warty, blue-grey cap that falls off as the flower opens. In Belgium it rarely flowers.

Fruit

A woody, ribbed capsule 1.5–2.5 cm across, shaped like a spinning top, with very fine seeds.

Bark

Smooth; peels off in long strips to reveal a smooth, grey to cream trunk. Some rougher bark often remains at the base.

Look-alikes

Eucalyptus gunnii, the eucalyptus most often seen in Belgian gardens, is much hardier and has small, round juvenile leaves of 2–4 cm and small flowers in threes. The Tasmanian blue gum has larger juvenile leaves and large, single buds with a warty cap.

Flowering: January–April · Pruning: April

Why grow it?

• Beautiful blue-grey juvenile foliage, ideal as cut foliage for bouquets and wreaths: it lasts well and smells fresh.
• Grows astonishingly fast: a seedling can reach 1–2 m in a single season.
• A striking trunk, with bark that peels off in long strips.
• Aromatic: the leaves smell fresh when crushed.
• In its home range and in southern Europe it flowers in winter and early spring and is an important source of nectar for bees and birds.

Tasmanian blue gum: where does it grow best?

• In Tasmania and Victoria in open forest on moist, deep soil in valleys and on slopes, in a mild, wet climate without hard frost.
• In Belgium: full sun, in a warm spot sheltered from cold east winds.
• Well-drained but moisture-retentive soil, preferably acid to neutral; no waterlogged soil or heavy clay. In a pot: compost with a little grit.
• In open ground only in a very mild, sheltered town or coastal garden, with the risk that it freezes in a hard winter. Usually it is grown in a pot or as a foliage plant for a single season.

Goes well with

• Blue fescue: A low, blue ornamental grass that echoes the blue-grey of the juvenile leaves.
• Russian sage: Silver-grey leaves and violet-blue flowers for bees, in the same sunny, dry spot.
• Lavender: Fragrant grey leaves and summer flowers for bees and butterflies.
• Catmint: A low, blue-flowered plant for the base that blooms for a long time and attracts bees.

Tasmanian blue gum: when and how to plant it?

1. Buy a young plant of 30–60 cm in a pot: eucalyptus establishes poorly if it has been in too small a pot for a long time.
2. Or sow indoors in February–March at 18–20 °C: scatter the fine seed on moist seed compost and cover it very lightly. Prick the seedlings out into individual pots as soon as they have two true leaves.
3. After mid-May, let young plants harden off for a week in partial shade before they go into full sun.
4. Plant in a large pot with a drainage hole, or in late May in open ground in a sheltered, sunny spot. Set it at the same depth as in the pot and water generously.
5. Put in a short stake and tie the trunk low: that way the trunk can move and grow strong, but the rootball is not rocked loose by the wind.
6. Never dig up plants in the wild: buy them from a nursery.

Care

Watering

Water young plants and pot plants regularly in summer; in open ground, after that only in long dry spells.

Feeding

Little: an occasional feed for container plants in May–July. Too much feeding gives soft wood that is easily frosted.

Overwintering

Bring a pot indoors in October, somewhere light and cool at 3–8 °C, and water sparingly.

Cut foliage

In summer, cut branches with juvenile leaves for bouquets; this also keeps the plant compact.

Staking

Tie the trunk low to a short stake for the first two years.

Tip: If it is mainly the blue juvenile foliage you want, treat it as a foliage plant: cut it back every spring or sow again each year. For a permanent eucalyptus tree in the garden, the much hardier Eucalyptus gunnii is a better choice.

Pruning and mowing

Pruning months: April.

When: In April, when the hardest frosts are over and the plant starts to grow again.

How:

• To keep the blue juvenile foliage, cut the plant back every spring to 30–60 cm above the ground: it regrows with juvenile leaves.
• Cut frosted branches back to live wood; wait until you can see where new buds are appearing.
• In a pot, shorten the leader and side branches to keep it compact.
• A tree you allow to grow on only needs pruning when there are dead or broken branches.

Caution: Do not prune in autumn: the new shoots then have no time to harden off and get frosted in winter.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Seed

Sow on the surface indoors in February–March at 18–20 °C. The seed usually germinates in 1–3 weeks. Prick out the seedlings young, because older plants do not like being moved.

Cuttings

Cuttings root with great difficulty; for gardeners, sowing is the only practical method.

Tasmanian blue gum: how does it get through the winter?

Hardy to −6 °C: protect in harsh winters.

• Not reliably hardy: older plants briefly survive about −5 to −7 °C, young plants and pot plants less.
• A frosted plant sometimes regrows from the base of the trunk, if the base has not frozen.
• Evergreen: in a mild winter the leaves stay a lovely blue-grey.
• In open ground, protect the base with a thick mulch; put a pot in a light, cool place.

Diseases and pests

• Frost damage: Brown, dried-out leaves and dead twigs after frost. Wait until April to cut back; it often regrows lower down the trunk.
• Wind-rock: Because of its fast growth and small rootball, it blows over easily. Plant young, use a low stake and reduce the crown.
• Circling roots: Plants left too long in a pot develop circling roots and never stand firm later. Buy young plants and pot on in good time.
• Pests in winter quarters: Mealybugs and scale insects on stems and leaves. Wipe them off with a cloth or soft brush and overwinter cool and light.

Through the year

• January: Pot in winter quarters: light, cool, little water.
• February: Sow indoors at 18–20 °C. In southern Europe it is in flower now.
• March: Prick out seedlings. In Belgium it rarely flowers.
• April: Cut back for new blue juvenile foliage. Remove frosted branches.
• May: After mid-May, move outside or plant out.
• June: Water. Pinch out tips for a bushier plant.
• July: Cut branches for bouquets. Water in dry spells.
• August: Harvest cut foliage. Last feed of the year.
• October: Bring the pot in before the first frost. Mulch plants in open ground.
• November: Winter quarters: light and cool, little water.
• December: Check for pests in winter quarters.

Did you know?

• The name Eucalyptus comes from the Greek eu (well) and kalyptos (covered): the flower bud is closed by a little cap that falls off when it flowers. Globulus means ‘little ball’.
• It is the floral emblem of Tasmania. There, the rare and endangered swift parrot depends heavily on the nectar of its flowers during the breeding season.
• In the 19th century it was planted around Rome, among other places, to dry out wet, malaria-ridden land; this earned it the nickname fever tree.