Warminster broom

Warminster broom: how do you recognise it?

Habit

Dense, rounded shrub 1–1.2 m tall and up to 1.5 m wide, with many thin, arching shoots.

Shoots and leaves

Green, finely ribbed shoots that take over much of the work of the leaves. The leaves are small, narrow and grey-green and drop early.

Flower

Small, cream-yellow pea flowers, singly or in pairs along the whole length of the shoots, in April–May.

Scent

The flowers have a heavy, sweetish scent that not everyone finds pleasant.

Fruit

After flowering, small, flat pods with poisonous seeds.

Roots

A deep taproot with nodules in which bacteria fix nitrogen from the air. It dislikes being moved.

Flowering: April–May · Plants: March–April and September–October · Pruning: May–June

Why grow it?

• A lavish spring display: in April–May every shoot is covered in cream-yellow flowers.
• The flowers attract bees and bumblebees.
• Ideal for poor, dry, sandy soil: it fixes its own nitrogen and needs no feeding.
• The green shoots give structure even in winter, although the small leaves drop early.
• Compact enough for a small garden, a rock garden, a bank or a large pot.

Warminster broom: where does it grow best?

• Full sun: in shade it hardly flowers and becomes floppy and bare.
• Poor, dry, well-drained soil: sand or light loam, acid to neutral.
• No wet or heavy soil: the roots rot there in winter.
• An open, warm spot; some shelter from strong wind stops the shoots being blown out of shape.
• Allow 1–1.5 m per plant; as a low hedge or on a bank, plant 80–100 cm apart.

Light

Sun

Soil type

Sand or loam

Acidity

Acid or neutral

Moisture

Dry

Size

1.2 m tall, 1.5 m wide

Hardiness

Hardy (to -20 °C)

Goes well with

• Heather: Enjoys the same poor, acid, sunny soil; together they make a colourful, low-maintenance heather garden.
• Lavender: Flowers in summer, after the broom, and sets silver-grey leaves next to the green shoots.
• Blue fescue: Blue tufts next to the yellow flowers, in the same dry spot.
• Rock rose: A low ground cover for the front, for sun and drought.
• Grape hyacinth: Little blue flowers at its feet, flowering in April together with the broom.

Warminster broom: when and how to plant it?

Plant in March–April and September–October.

1. Plant in March–April or September–October.
2. Choose a young pot-grown plant: broom establishes poorly if its taproot is damaged, and moving a larger plant rarely works.
3. Dig a hole twice as wide as the pot; on heavier soil, mix coarse sand or grit into the soil. No compost or fertiliser.
4. Ease the plant out of its pot without breaking the root ball and set it at the same depth as it was in the pot.
5. Water in well and water in prolonged dry spells during the first year.
6. In a windy garden, give it a short stake for the first year.

Care

Watering

Only in dry spells in the first year. After that it manages without; too much water is worse than too little.

Feeding

Not needed: it fixes its own nitrogen. Fertiliser makes it floppy and shortens its life.

After flowering

Cut back the faded shoots every year (see pruning); it then sets less seed and stays dense.

Snow

Shake wet snow off the shrub, or the shoots may split or bend out of shape.

Lifespan

Broom is not long-lived: after ten years or so it often becomes bare and woody. Replace it with a young plant.

Tip: Start pruning every year after flowering while the plant is young: that keeps the shrub dense and compact. A broom that has gone bare is better replaced with a new plant.

Warminster broom: when to prune it?

Pruning months: May–June.

When: Straight after flowering, in late May or June. Start when the plant is young and prune every year, or it soon becomes bare.

How:

• Cut back the shoots that have flowered by up to two-thirds, just above a young side shoot.
• Always stay in the green, young wood: never cut into the old, brown branches.
• Remove dead and broken shoots.
• An old, bare broom cannot be rejuvenated by hard pruning: replace it with a young plant.

Caution: Broom does not reshoot from old, brown wood: cutting into it leaves bare stumps.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Semi-ripe cuttings

In July–August, take 8–10 cm cuttings from young side shoots, ideally with a heel of older wood. Put them in sandy cutting compost in a cold frame or under plastic. Pot them up separately in spring, before the taproot grows too long.

Seed

Not worthwhile: as a hybrid it does not come true from seed. Take cuttings or buy a young plant.

Warminster broom: how does it get through the winter?

Hardy to −20 °C.

• Hardy to about −20 °C: in Belgium it comes through normal winters without protection.
• Wet soil in winter is more dangerous than frost: make sure drainage is good.
• Shake heavy snow off the shoots so they do not split.
• In a pot: stand it against a sheltered wall, wrap the pot in hessian and keep the compost on the dry side.

Diseases and pests

• Becoming bare: The shrub becomes woody and bare at the base and only flowers at the tips. Prevent it with yearly pruning after flowering; replace an old plant.
• Root rot: Branches suddenly die on wet, heavy soil. Little can be done: plant a new broom in a drier spot or a raised bed.
• Aphids: On young shoots in spring. Ladybirds usually deal with them; otherwise spray them off with water.
• Broom gall mite: Small, cauliflower-like growths on the shoots, caused by a mite. Cut out affected shoots and put them in the household waste.

Through the year

• January: Shake wet snow off the shoots.
• March: Plant. No fertiliser.
• April: Flowering begins; bees and bumblebees on the flowers.
• May: In full flower. Straight after flowering, cut back the faded shoots.
• June: Finish pruning after flowering, before the pods ripen.
• July: Take semi-ripe cuttings. Water young plants in dry spells.
• August: Take cuttings.
• September: Plant.
• October: Plant pot-grown plants before winter.

Edible and useful

Not edible. Broom and Spanish broom are poisonous in all their parts, especially the seeds in the pods: their alkaloids cause nausea and vomiting, among other things. The flat pods look like those of peas or beans, and the yellow flowers are not edible flowers. Teach children not to open the pods, and do not plant broom in or next to a field: horses, sheep and goats, and dogs and cats too, can fall ill from it. 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.

Did you know?

• It arose around 1867 as a chance cross in a nursery at Warminster, in southern England; that is where its English name comes from.
• Its parents are two brooms from south-western Europe: Cytisus multiflorus, with white flowers, and the yellow-flowered Cytisus purgans.
• Praecox means ‘early’: it flowers earlier than most other brooms.