Stone pine

Stone pine: how do you recognise it?

Habit

Round and bushy when young; later a bare trunk with a broad, flat umbrella crown. In open ground up to about 15 m tall and 10 m wide, usually smaller here.

Needles

In pairs, 10–20 cm long, stiff, grey-green to dark green. Young plants carry short, single, blue-green juvenile needles for the first few years.

Cones

Large, ovoid to rounded, 8–15 cm, glossy brown; they only ripen in their third year.

Seeds

Large seeds with a hard shell: the pine nuts. Here they rarely ripen properly.

Bark

Reddish brown to grey, deeply fissured and flaking in plates.

Roots

A deep taproot: transplant it young and not too often.

Plants: April–May and September · Pruning: May–June

Why grow it?

• A touch of the Mediterranean in the garden or on the terrace, green all year round.
• Excellent tolerance of drought and heat once well established.
• Young trees stay compact for years and look good in a large pot.
• The large, glossy cones are decorative.
• Low maintenance: it needs hardly any pruning.

Stone pine: where does it grow best?

• Full sun, in the warmest spot in the garden.
• Light, well-drained soil: sand or loam, acid to chalky.
• Dry; it does not tolerate wet soil, especially in winter.
• Sheltered from cold east and north winds.
• In open ground it will eventually need a lot of space; in a pot it stays compact for years.

Light

Sun

Soil type

Sand or loam

Acidity

Not fussy

Moisture

Dry

Size

15 m tall, 10 m wide

Hardiness

Hardy (to -15 °C)

Goes well with

• Lavender: Mediterranean scent and colour in the same sunny, dry spot.
• Rosemary: Evergreen and just as fond of warmth and drainage.
• Rock rose: A flowering shrub for the dry, sunny border.
• Feather grass: Swaying plumes that soften the stiff silhouette.
• Thyme: A fragrant ground cover in the gravel at the base.

Stone pine: when and how to plant it?

Plant in April–May and September.

1. Plant in April–May so the roots can establish well before winter; on light soil September also works.
2. Dig a generous hole and, on heavier soil, mix in coarse sand or gravel for good drainage.
3. Set the tree at the same depth as in the pot and do not damage the taproot.
4. In a pot: choose a heavy pot with a drainage hole, put a layer of gravel in the bottom and use potting compost mixed with one third coarse sand or grit.
5. Water well after planting and keep the soil lightly moist through the first season.
6. Mulch with gravel rather than compost: this keeps the base dry.

Care

Water

In open ground only in the first year during dry spells. In a pot, regularly in summer, but let the top few centimetres dry out in between.

Feeding

Not needed in open ground. In a pot, a little organic fertiliser in April.

Repotting

Every two to three years in March–April into a slightly larger pot, with fresh, free-draining compost.

Pot feet

Stand a pot on pot feet so excess water can always drain away.

Frost protection

Keep a fleece to hand in winter for young trees and pots (see winter).

Tip: Choose a spot that is never wet and, for container growing, a heavy pot with a good drainage hole. Wet roots in winter kill more stone pines than frost does.

Stone pine: when to prune it?

Pruning months: May–June.

When: Real pruning is not needed. In May–June you can shorten the young shoots, the ‘candles’, to keep the tree compact.

How:

• Pinch or snap the young candles back by half, before the new needles have fully expanded.
• Remove dead or damaged branches back to the trunk or a healthy side branch.
• For an umbrella crown, gradually remove the lowest branches, a few each year.
• Do not cut into old wood without needles: a pine will not regrow from it.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Seed

Sow fresh, untreated seeds in April about 2 cm deep in deep pots. Keep them warm and lightly moist; they usually germinate within a few weeks. Pot on the seedlings young because of the taproot. Shop-bought pine nuts rarely germinate: they are often processed or from another species.

Cuttings

Pines hardly root from cuttings; seed is the practical method.

Stone pine: how does it get through the winter?

Hardy to −15 °C: protect young plants.

• Hardy to about −15 °C. In a normal Belgian winter it survives in open ground in a sheltered, dry spot; young plants are more vulnerable.
• Wet soil combined with frost is the greatest danger: ensure good drainage.
• In severe frost and cold wind the needles may turn brown; protect young trees with fleece at such times.
• In a pot the roots freeze more quickly: wrap the pot and stand it against a wall, or in severe frost move it to a cold, light place such as an unheated greenhouse.

Diseases and pests

• Root rot: Yellow needles and a declining tree on wet soil or in a pot without drainage. Improve drainage; badly affected trees cannot be saved.
• Frost damage: Brown needles after a hard winter. Wait for spring: as long as the buds are alive, it will grow again.
• Pine sawfly: Groups of green, caterpillar-like larvae strip the needles in summer. Pick them off by hand or cut off the twig.
• Pine woolly aphid: White, woolly tufts on shoots and needles. Spray off with water or brush them away.
• Drying out in a pot: Brown needle tips in summer. Water more regularly, preferably in the morning.

Through the year

• January: Protect the pot in severe frost. Water sparingly.
• February: Check frost protection.
• March: Remove protection in mild weather. Repot.
• April: Plant. Sow. Give potted trees a little fertiliser.
• May: Plant. Shorten the candles for a compact shape.
• June: Finish pinching the candles. Water pots regularly.
• July: Water pots in dry spells. Watch for sawfly larvae.
• August: Water pots in dry spells.
• September: Plant on light soil.
• November: Stand the pot on pot feet and move it against a wall.
• December: Wrap the pot. In severe frost, fleece over young trees.

Did you know?

• The cones take about three years to ripen, longer than in most other pines.
• The stone pines in and around Rome inspired the Italian composer Ottorino Respighi to write his symphonic poem ‘Pini di Roma’ in 1924.
• For the first few years, young seedlings have single, blue-green juvenile needles; the long paired needles only appear later.