Blackthorn

Blackthorn: how do you recognise it?

Habit

Dense, thorny shrub of 1–4 m that forms wide thickets through suckers.

Leaf

Alternate, small (2–4 cm), oval and finely toothed.

Bark

Dark, almost black, with sharp, thorny side shoots.

Flower

Small white flowers, massed on the bare branches in March–April.

Fruit

Blue sloes with a waxy bloom; astringent, better after frost (sloe gin).

Difference from hawthorn

Hawthorn has lobed leaves and flowers in May, after the leaves.

Flowering: March–April · Harvest and fruit: October–November · Pruning: June–August and November–February

Identify by feature: White blossom · Blue berries · Thorns or prickles

Looks like it, but isn’t

• Hawthorn Crataegus monogyna: lobed leaves and flowers in May, after the leaves. Difference from hawthorn

Why grow it?

• White blossom in March–April, one of the first sources of nectar for bees.
• A thorny thicket: a safe nesting place for birds.
• Sloes for liqueur and jelly, after the first frost.
• Food plant of the rare brown hairstreak.

Blackthorn: where does it grow best?

• Full sun; in shade it flowers and fruits little.
• Any soil, dry or moist, including chalky soil.
• Allow 3 m width, and more if you let the suckers spread.
• At home in a mixed hedge, hedgerow or wild edge; because of the suckers, less suited next to a lawn or border.

Light

Full sun

Legal basis

Any garden soil

Moisture

Dry to wet

Size

4 m tall, 3 m wide

Hardiness

Throughout Belgium, no protection needed

Goes well with

• Hawthorn: Flowers just after blackthorn: together a thorny native hedge full of blossom and berries.
• Dog rose: Flowers in June and hips in autumn, for the same sunny hedge.
• Hazel: Catkins in January, blackthorn blossom in March: an early spring for bees.
• Spindle: Pink fruit in autumn alongside the blue sloes.

Good and bad companions

Goes well with

• Together a mixed native hedge, good for birds and insects: hawthorn, hazel, dog rose, common dogwood, guelder rose, wild privet, field maple, hornbeam

Best kept away from

• Do not plant under the dense crown of these trees: norway spruce, european silver fir, nordmann fir, douglas fir, yew, horse chestnut, norway maple, sycamore

Blackthorn: when and how to plant it?

1. Plant from November to March, bare-root.
2. In a mixed hedge: place it among hawthorn, dog rose and hazel, preferably on the sunny side.
3. After planting, cut the branches back to 20–30 cm so that it bushes out densely from below.
4. To limit suckers, bury a root barrier or plant it where you can mow all around.

Care

Watering

Only in dry spells during the first year.

Feeding

Not needed.

Suckers

Regularly mow or dig out suckers outside the hedge; young suckers can also be replanted.

Harvest

Pick the sloes in October–November, ideally after the first frost.

Tip: If you pick the sloes before the frost, put them in the freezer overnight: they come out softer and less astringent.

Blackthorn: when to prune it?

Pruning months: June–August and November–February.

When: In winter as a shrub; after flowering as a hedge.

How:

• A freely growing shrub: now and then in winter, saw the oldest stems off at the base.
• A hedge: trim it into shape in summer after flowering, preferably not the whole hedge every year.
• Wear sturdy gloves: blackthorn pricks easily become infected.

Caution: Before summer pruning, check that no birds are nesting, and never cut everything at once: the eggs of the brown hairstreak overwinter on the young twigs.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Suckers

In winter, dig up a sucker with roots and replant it separately; nothing could be easier.

Sowing

Sow the stones outdoors in autumn; they often only germinate after eighteen months.

Blackthorn: how does it get through the winter?

Hardy throughout Belgium: no protection needed.

• Fully hardy.
• The sloes hang on into winter: food for thrushes and other birds.

Diseases and pests

• Suckers: It conquers its surroundings with suckers. Mow or dig them out regularly, or plant it where they do no harm.
• Ermine moths: Caterpillars sometimes wrap the whole shrub in a silvery web and strip it bare. It looks dreadful, but the shrub simply leafs out again in summer.
• Prick wounds: Thorn pricks easily become infected. Wear sturdy gloves and disinfect any prick properly.
• Few flowers or fruit: Too much shade, or frost during flowering. Give it a sunny spot.

Through the year

• January: Winter pruning of freely growing shrubs.
• February: Last winter pruning; dig out suckers.
• March: White blossom on the bare branches: first nectar for bees.
• June: Trim the hedge after flowering; watch out for nests.
• July: Hedge trimming.
• August: Last hedge trim; the sloes turn blue.
• October: Sloes ripen; wait for the first frost.
• November: Pick sloes and plant; winter pruning can begin.
• December: Winter pruning.

What can you use it for?

Food and drink

Sloes for liqueur (sloe gin) and jelly, ideally after the first frost.

For wildlife

Early flowers for bees; nesting sites and berries for birds.

Caution: Produces lots of suckers.

Edible and useful

Fruit (October–November)

Sloes are ripe when they are blue-black with a bloom and give slightly when pressed, usually in October–November. After the first frost, or a night in the freezer, they are less astringent. Too sour to eat as they are, but delicious in liqueur, jelly, syrup or cooked with apple.

Storing

Freeze sloes: that way you also give berries picked before the frost their ‘frost’. Liqueur and jelly keep for a long time.

Caution: As in all Prunus species, the stone contains substances that can release cyanide: do not crack or grind the stones, and leave them whole in liqueur and jelly. Do not confuse sloes with poisonous black berries such as those of privet, alder buckthorn or purging buckthorn: a sloe is a small plum with a hard stone, on a shrub with sharp thorns. Pick away from busy roads and sprayed fields.

Eating and using is at your own risk: see the terms of use.

Recipes

• Sloe gin (Liqueur · ± 1 litre · 20 min + 3 months steeping)
• Sloe and apple jelly (Jelly · ± 4 jars · 1 hour + overnight draining)
• Fermented sloe ‘olives’ (Fermentation · ± 1 jar of 500 ml · 20 min + 3–4 weeks fermenting)
• Sloe ketchup (Other · ± 500 ml · 1 hr)

Good for wildlife

Caterpillars

Host plant: caterpillars of butterflies or moths eat the leaves.

Bees

Nectar and pollen for honeybees and wild bees.

Birds

Berries, seeds or insects as food, or a place to nest.

Hoverflies

Open flowers for hoverflies; many of their larvae eat aphids.

Hedgehogs

Shelter and a layer of leaf litter full of insects.

Did you know?

• Food plant of the rare brown hairstreak, a small brown butterfly.
• The red-backed shrike impales insects and mice on its thorns, as a larder.
• In Ireland its hard, tough wood was used for the shillelagh, a traditional walking stick.
• A cold spell while blackthorn is in flower is known in English as a ‘blackthorn winter’, and in German as ‘Schlehenwinter’.
• The shillelagh, the traditional Irish walking stick and cudgel, has long often been cut from blackthorn wood.