Pinus cembra aka Arolla Pine

Pinus cembra, the Swiss stone pine, is an evergreen conifer in the pine family, Pinaceae. Other names include Arolla pine and Siberian cedar pine. It grows wild in the mountains of central and eastern Europe. Some sources extend its range into parts of Asia.

This is a slow-growing tree. In gardens it usually reaches 25 to 40 feet (8 to 12 m) tall and 10 to 25 feet (3 to 8 m) wide. In its mountain home it can reach about 70 to 80 feet (20 to 24 m). Young trees are dense and narrowly pyramidal, with branches down to the ground. With age the crown opens out, becomes broader and may flatten on top. The RHS suggests a tree may need more than 50 years to reach full size.

The needles come in bundles of five and measure about 2 to 3 inches (5 to 8 cm). They are stiff and straight yet soft to the touch, with finely toothed edges. Their colour ranges from dark green to blue-green. Bluish-white lines of stomata mark the inner faces. Each needle stays on the tree for up to five years, which gives the crown a full look. Young shoots carry a dense coat of orange-brown hairs. The bark darkens with age and breaks into scaly, fissured plates.

The tree has no true flowers. It bears separate male and female cones on the same plant, and they appear in March and April. The seed cones are egg-shaped and about 2 to 3 inches (5 to 8 cm) long. They start greenish-violet or blue-green and ripen to purplish brown. The scales never open. The cones fall and rot, and birds spread the large, wingless seeds. Small mammals eat the seeds too. The caterpillars of the imperial moth feed on the foliage.

Give this pine full sun and well-drained soil. Loam and sand both suit it, and it accepts acid, neutral or alkaline conditions. Shallow chalk soils may shorten its life. Once settled it copes with dry spells. It is very cold-hardy, rated H7 in the UK and roughly USDA zones 3 to 7. It dislikes hot, humid summers. Good air movement helps, and young trees transplant well. Pruning is rarely needed. If a young tree forms two leaders, remove one. Do any cutting between late summer and midwinter, because the wood is resinous.

Gardeners value it as a specimen or accent tree. Its narrow, tidy shape stays in scale with smaller gardens for many years. It also works in groups or as a screen. The tree can be hard to find in nurseries. Several cultivars exist, from columnar to dwarf forms. Deer tend to leave it alone.

Most sources call it resistant to pests and diseases. It shows good resistance to blister rust. Possible pests include adelgids, conifer aphid, sawfly larvae and pine shoot moth. Caterpillars, borers, bark beetles, miners, scale and mealybugs may also attack it. Possible diseases include honey fungus, needle cast, blights, rots, canker and rusts. Strong wind can damage it. The large seeds inside the cones are edible.