Blue holly

Blue holly: how do you recognise it?

Habit

Dense, upright shrub about 2–2.5 m tall and 1.5 m wide; fairly slow-growing.

Leaves

Oval, 3–6 cm long, glossy blue-green with spiny teeth along the edge, on purple twigs.

Flower

Small white flowers in the leaf axils in May. Male and female flowers are on separate plants.

Berries

Glossy red, about 1 cm, only on female plants and only if there is a male holly nearby.

Roots

Fairly shallow and branched; older plants do not move well.

Flowering: May · Plants: April–May and September–October · Pruning: April and August

Why grow it?

• Green all year, with a blue sheen that is rare among evergreens.
• Red berries on female plants from autumn well into winter: decorative and food for thrushes and blackbirds.
• The small May flowers provide nectar and pollen for bees.
• Ideal as a dense hedge or clipped into shape; the spines deter unwanted visitors.
• Grows in sun, partial shade and even shade.

Blue holly: where does it grow best?

• Sun, partial shade or shade; in sun it becomes densest and carries the most berries.
• Any well-drained garden soil: sand, loam or clay, acid to chalky.
• Moderately moist; it dislikes waterlogging and long droughts.
• Somewhat sheltered from bright winter sun and cold, drying winds, which can scorch the leaves.
• Plant single shrubs 1.5 m apart, a hedge 40–50 cm apart. One male plant nearby can pollinate several females.

Light

Sun, partial shade and shade

Soil type

Sand, loam or clay

Acidity

Not fussy

Moisture

Normal

Size

2.5 m tall, 1.5 m wide

Hardiness

Hardy (to -25 °C)

Goes well with

• Christmas rose: White flowers in winter at the foot of the dark leaves.
• Snowdrop: A white carpet in February beneath the evergreen shrub.
• Witch hazel: Fragrant yellow or orange winter flowers beside the red berries.
• Red-barked dogwood: Red winter stems as a contrast to the blue-green leaves.
• Ferns: Fresh underplanting for the shady side.

Blue holly: when and how to plant it?

Plant in April–May and September–October.

1. Plant in April–May or September–October.
2. Dig a hole twice as wide as the root ball and mix in some compost.
3. Set the plant at the same depth as it was in the pot or root ball and firm the soil well.
4. Leave 1.5 m between single shrubs, or 40–50 cm for a hedge.
5. Water thoroughly straight away and regularly in dry weather during the first year.
6. Spread a mulch of leaf mould or bark around the base.

Care

Water

Regularly in dry weather in the first year, including a dry spring. After that only in long dry spells.

Feeding

Some compost or organic fertiliser in April.

Mulching

A layer of leaf mould keeps the soil cool and moist.

Pollination

Berries only form on female plants with a male nearby; ‘Blue Prince’ is a good pollinator.

Gloves

Wear sturdy gloves when pruning and clearing up: the leaves prick.

Tip: Plant one male holly, such as ‘Blue Prince’, among the female plants: it can pollinate several, so they all carry plenty of berries.

Blue holly: when to prune it?

Pruning months: April and August.

When: In April or late August, if you want to keep it in shape. A free-standing shrub hardly needs pruning.

How:

• Trim a hedge once a year, in April or late August, with shears or secateurs.
• Keep a hedge slightly wider at the bottom than at the top, so it stays leafy right down to the ground.
• Prune female plants moderately: the harder you cut, the fewer flowers and berries.
• Remove dead or damaged branches back to healthy wood.

Caution: Wear sturdy gloves and clear up prickly clippings and fallen berries, especially where children or pets go.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Semi-ripe cuttings

In August–September take 10–15 cm cuttings with a heel and insert them in moist cutting compost under plastic or in a cold frame. They root slowly, often only after several months.

Layering

In spring, make a small cut in a low branch, lay it in the soil and peg it down. Sever and replant after 1–2 years.

Seed

Takes 1–3 years to germinate, and you cannot tell whether the plant will be male or female. Not worth it for the garden.

Blue holly: how does it get through the winter?

Hardy to −25 °C.

• Hardy to about −25 °C, and hardier than common holly: in Belgium it needs no protection.
• Bright winter sun on frozen ground can turn leaves brown: a spot with some winter shade helps.
• The red berries often stay on until late winter, until the birds eat them.
• In a pot: stand it against a wall and wrap the pot in hessian in severe frost.

Diseases and pests

• Holly leaf miner: Yellow to brown blotches and tunnels in the leaves, made by the larvae of a small fly. Harmless to the plant; cut off badly affected leaves.
• Scale insects: Small brown or white scales on twigs and under the leaves, often with sticky leaves. Brush them off or wash the leaves with a mild soap solution.
• No berries: The plant is male, or there is no male holly nearby. Plant a male pollinator.
• Brown leaves: Caused by winter sun on frozen ground, drought or waterlogging. Ensure good drainage, water in dry weather and give some winter shade.

Through the year

• April: Plant. Prune into shape. Give compost.
• May: Small white flowers. Plant.
• June: Water in dry weather.
• August: Trim a hedge in late August. Take semi-ripe cuttings.
• September: Plant. Take cuttings.
• October: Plant. The berries turn red.
• November: Red berries: food for thrushes and blackbirds.
• December: Cut sprigs with berries for Christmas decorations, out of reach of children and pets.

Edible and useful

Not edible. Holly berries and leaves are poisonous: a few berries can cause vomiting, stomach ache and diarrhoea in a child, and dogs and cats fall ill from them too. The glossy red or black berries stay on the plant well into winter, and come indoors too with branches for Christmas decorations. Do not plant female plants where small children play, pick up fallen berries and hang decorations with berries out of their reach. Birds, however, eat the berries without harm. If any is swallowed, call a poison centre (in Belgium 070 245 245) or your doctor at once.

Good for wildlife

Bees

Nectar and pollen for honeybees and wild bees.

Birds

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

Did you know?

• It was raised by Kathleen Meserve, an amateur gardener on Long Island near New York, and is named after her.
• Holly is dioecious: each plant is male or female, and only female plants carry berries.
• Thanks to its Japanese parent it copes with severe frost better than common holly.