Cranberry

How to recognise it

Habit

Creeping dwarf shrub only 5–15 cm high, with thread-like stems up to 80 cm long across the sphagnum.

Stem

Thread-thin and reddish brown; it roots where it lies on damp sphagnum.

Leaf

Small (4–8 mm), oval, leathery and evergreen; dark green above, bluish white below, with a rolled-under edge.

Flower

Pink, with four strongly swept-back petals and a pointed bundle of stamens, on long, thin stalks, from May to July.

Fruit

Round berry 8–15 mm across, pale with red speckles at first, deep red when ripe; ripe from August to October.

Confusion with

Small cranberry is even smaller, with hairless flower stalks and smaller berries. Bog rosemary is upright, with longer, narrow leaves and bell-shaped flowers. Cowberry has larger leaves and pinkish-white bells.

Flowering: May–July · Pruning: April

Why grow it?

• Food plant of the cranberry fritillary, a rare butterfly of the Ardennes bogs.
• The flowers are visited by bumblebees, which shake out the pollen by buzzing.
• A characteristic plant of living raised bog: where it grows, conditions are wet, acid and nutrient-poor.
• Evergreen, with red berries that can stay on the plant into winter.
• The berries are edible: sour, but tasty in compote or sauce, just like those of the related American cranberry.

Cranberry: where does it grow best?

• In the wild in raised bogs, wet heath and on sphagnum hummocks beside moorland pools.
• Always wet, acid and very nutrient-poor, fed by rainwater.
• Sun to light partial shade.
• In the garden: only in a bog bed or a wide pot with acid, lime-free compost that stays wet at all times, watered with rainwater.

Goes well with

• Round-leaved sundew: A small carnivorous plant that grows on the same wet sphagnum.
• Bog rosemary: Pink bells and blue-green leaves in the same bog bed.
• Cross-leaved heath: Pink flowers in summer on wet, acid soil.
• Common cottongrass: White tufts above the sphagnum in late spring.
• Sphagnum moss: The basis of the bed: it holds water and makes the soil acid.

Cranberry: when and how to plant it?

1. Buy plants from a nursery specialising in native or lime-hating plants; never take plants or sphagnum from a bog.
2. Make a bog bed: a hole 30–40 cm deep lined with pond liner with a few holes pricked in the bottom, or a wide, shallow pot.
3. Fill with lime-free sand mixed with peat-free ericaceous compost, and add some cultivated sphagnum on top if you like.
4. Plant in April–May or in September, 20–30 cm apart, and press the stems lightly onto the surface.
5. Water only with rainwater, because tap water contains lime; the compost must never dry out.

Care

Watering

Keep wet at all times with rainwater. Check daily in dry summers.

Feeding

Never: bog plants are made for poor soil, and fertiliser kills them.

Weeding

Remove grasses, soft rush and birch seedlings, or they will take over the bed.

Fallen leaves

Remove leaves that fall from trees; they enrich the acid bed.

Lime

Do not use lime, ordinary compost or tap water.

Tip: Collect rainwater in a butt next to the bog bed: in a dry summer it makes the difference between a living bed and a dead one.

Pruning and mowing

Pruning months: April.

When: Hardly needed; if at all, in April.

How:

• In April, shorten runners that grow out of the bed.
• Otherwise let the stems creep freely: they root and form a carpet.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Layering

Stems root by themselves in damp sphagnum; in spring, cut off a rooted piece and replant it.

Cuttings

In June–July, insert 10 cm stem pieces in damp, acid compost; they root fairly easily.

Seed

Sow seed from ripe berries in autumn on acid compost; it needs a cold spell and grows slowly.

Cranberry: how does it get through the winter?

Hardy to −30 °C.

• Evergreen: in the cold the leaves often turn reddish brown.
• Ripe berries sometimes stay on the plant into winter or even spring.
• Very hardy: it grows far into northern Europe.
• A pot can freeze solid and dry out: put it in a sheltered spot and keep the compost moist.

Diseases and pests

• Drying out: The most common cause of death in gardens. Keep the bed wet at all times and water with rainwater in dry spells.
• Yellow leaves: A sign of lime or too many nutrients. Use only rainwater and no compost.
• Being overgrown: Grasses, soft rush and birch crowd it out. Weed regularly.
• Few berries: Too much shade or a summer that was too dry. Give more light and keep the bed wet.

Through the year

• March: Check and weed the bed.
• April: Plant. Shorten long runners.
• May: First flowers.
• June: Full flower: bumblebees. Take cuttings.
• July: Last flowers. Water daily in dry weather.
• August: The berries turn red.
• September: Pick berries. Plant.
• October: Pick berries. Sow seed.
• December: Rest. The leaves turn reddish brown.

Did you know?

• The name cranberry comes from crane berry: the flower with its swept-back petals and protruding stamens looks like the head and neck of a crane.
• Oxycoccos comes from Greek and means ‘sour berry’.
• The cranberry sold in shops is a related North American species, the American cranberry (Vaccinium macrocarpon), which has even gone wild on the Dutch island of Terschelling.