Black spruce

Black spruce: how do you recognise it?

Habit

The species: narrow, conical to columnar tree about 10 m tall and 4 m wide. ‘Nana’: a ball 0.5–1 m tall and wide, growing very slowly.

Needles

Short, 0.6–1.5 cm, square in cross-section, blue-green to blue-grey, packed close along the twigs.

Cones

Small, egg-shaped, 1.5–3 cm, grey-brown; they stay on the tree for years.

Bark

Thin, grey-brown and flaking.

Roots

Shallow and widely spreading: keep the soil cool and moist.

Plants: April–May and September–October

Why grow it?

• Extremely hardy, to about −45 °C.
• Tolerates acid, moist to wet soil that many other conifers struggle with.
• The dwarf form ‘Nana’ is a compact, blue-grey ball for a rock garden, heather garden, pot or small garden.
• Evergreen: structure and colour all year round.
• Low maintenance: no pruning needed.

Black spruce: where does it grow best?

• Sun to partial shade; ‘Nana’ stays densest in full sun.
• Acid, humus-rich soil: sand or loam, also peaty. No lime.
• Normal to moist: it tolerates a damp spot, but hot, dry soil is not for it.
• A cool, airy position; avoid warm walls and hot, dry corners.
• Allow 4 m width for the species; 0.5–1 m for ‘Nana’.

Light

Sun and partial shade

Soil type

Sand, loam or peat

Acidity

Acid

Moisture

Normal or wet

Size

10 m tall, 4 m wide

Hardiness

Hardy (to -45 °C)

Goes well with

• Heather: Low, colourful planting on the same acid soil.
• Dwarf rhododendron: Likes the same acid, moist soil and flowers in spring.
• Blueberry: Acid soil, lovely autumn colour and edible berries; a low shrub alongside.
• Ferns: Soft, green contrasts in partial shade.

Black spruce: when and how to plant it?

Plant in April–May and September–October.

1. Plant in April–May or in September–October, when the soil is neither frozen nor waterlogged.
2. Dig a hole twice as wide as the root ball and just as deep. Mix the excavated soil with acid leaf mould or pine bark.
3. Set the plant at the same depth as in its pot or root ball: the root collar stays at soil level.
4. Give the species 4–5 m from other trees and buildings; set ‘Nana’ at least 60 cm from neighbouring plants.
5. Water generously straight away, preferably with rainwater.
6. Spread a layer of pine bark or leaf mould mulch around the base, keeping it clear of the trunk.

Care

Water

Keep the soil slightly moist and water generously in dry spells, older plants included and ‘Nana’ in a pot above all.

Feeding

In spring, a thin layer of acid compost or a fertiliser for ericaceous conifers. Do not overfeed.

Mulching

Pine bark or leaf mould keeps the soil cool, moist and acid.

Spraying

In warm, dry weather, spray ‘Nana’ with a hose now and then, including beneath the branches: this keeps spider mite away.

Soil acidity

Do not use lime or lime-rich fertiliser, and use rainwater as much as possible.

Tip: Give it cool, acid soil and use rainwater. If ‘Nana’ grows in a warm, dry garden, a thick mulch of pine bark and regular spraying help against spider mite.

Black spruce: when to prune it?

When: It does not need pruning: the shape stays neat by itself. Only remove dead or damaged branches if necessary.

How:

• Cut dead or damaged branches back to the trunk or a side branch.
• On the species, remove a double leader and leave one strong leader.
• On ‘Nana’ it is better to do nothing: the compact ball shape does not recover after hard pruning.

Caution: Never cut into bare wood without needles: a spruce will not regrow from it.

Pruning calendar and basic rules

Propagation

Seed

Mainly for the species: collect the cones in autumn, let them dry and shake out the seeds. Sow them in spring on damp, acid compost and barely cover them; a cold period over winter helps.

Grafting and cuttings

‘Nana’ and other selections are propagated by nurseries by grafting or from cuttings; seedlings do not come true to the parent plant.

Black spruce: how does it get through the winter?

Hardy to −45 °C.

• Very hardy, to about −45 °C: no protection is needed.
• In a pot: put the pot in a sheltered spot and wrap it in hessian so the roots do not freeze. Water in dry, frost-free weather, because evergreens keep losing moisture.
• Late winter sun can scorch the needles on the sunny side; hessian or some shade helps.

Diseases and pests

• Spider mite: Fine webbing and pale, dried-out needles, mainly on the inside, in heat and drought. Hold a sheet of white paper under a branch and tap it: tiny moving dots are mites. Spray regularly with a strong jet of water and water generously.
• Brown needles: Needles turn brown from summer drought or from drying out in frost. Keep the soil moist and water in winter too, in dry, frost-free weather.
• Yellow needles: Pale foliage on chalky soil (chlorosis). Add acid compost and rainwater, and mulch with pine bark.
• Aphids: Now and then on young shoots, sometimes with sticky honeydew. Spray them off with water; ladybirds help.

Through the year

• January: Rest. Protect pots from frost and water them in dry, frost-free weather.
• March: Late winter sun: protect pots and young plants with hessian if needed.
• April: Plant. Give acid compost or a fertiliser for conifers.
• May: Plant. Apply mulch. Light green new shoots.
• June: Water in dry weather. Check for spider mite.
• July: Spray in dry, warm weather. Water.
• August: Water in dry and hot weather.
• September: Plant. The cones ripen.
• October: Plant. Water new plantings.
• November: Move pots to a sheltered spot or wrap them against frost.
• December: Rest. Water pots in dry, frost-free weather.

Did you know?

• In the wild it also spreads in bogs by natural layering: low branches take root, and a ring of smaller trees can form around a parent tree.
• The small cones often stay closed on the tree for years and release their seeds mainly after a forest fire.
• It is one of the commonest trees of the northern coniferous forests of North America.