Hardy plumbago

Hardy plumbago: how do you recognise it?

Habit

Low, creeping mat 25–30 cm tall and 40 cm or more across; spreads by underground runners.

Leaves

Oval, fresh green and alternate on reddish stems; bright red in autumn.

Flower

Small, flat flowers with five lobes in dense clusters at the stem tips, from August to October.

Colour

Deep gentian blue; the flowers open one after another, so flowering lasts for weeks.

Roots

Shallow, creeping rhizomes: it can spread well in a good spot, but is easy to keep in check with a spade.

Flowering: August–October · Plants: April–May · Pruning: March

Why grow it?

• Late flowering from August into October, in an unusually intense gentian blue.
• Blue flowers and red autumn leaves at the same time: one of the finest autumn combinations in a single plant.
• A dense, low ground cover that keeps weeds down in sunny, dry spots.
• Bees and butterflies find nectar here when many other flowers are already over.
• Copes with drought and poor soil once it is well established.

Hardy plumbago: where does it grow best?

• Full sun gives the most flowers and the best autumn colour; light partial shade is fine too.
• Free-draining sandy or loamy soil, acid to chalky; avoid heavy clay that stays wet in winter.
• Dry to moist: once established it copes well with drought.
• A warm spot at the foot of a wall, in a rock garden or between paving stones is ideal.
• Plant 30–40 cm apart, or 6–8 plants per m² for quick ground cover.

Light

Sun and partial shade

Soil type

Sand or loam

Acidity

Not fussy

Moisture

Dry or normal

Size

0.3 m tall, 0.4 m wide

Hardiness

Hardy (to -20 °C)

Goes well with

• Crocus: Small spring bulbs flower in the mat before the plumbago comes up.
• Ice plant: Pink to rusty-red flat flower heads at the same time, in a dry, sunny spot.
• Lavender: Grey leaves and summer flowers, also happy dry and sunny.
• Feather grass: Light, swaying stems above the low blue mat.
• Michaelmas daisy: Lilac and pink flowers in autumn.

Hardy plumbago: when and how to plant it?

Plant in April–May.

1. Plant in April–May, once the soil has warmed up: that is when it roots fastest.
2. Loosen the soil and, on heavy ground, work in coarse sand or fine gravel to improve drainage.
3. Dig a hole slightly wider than the pot and set the plant at the same depth as it was in the pot.
4. Leave 30–40 cm between plants; they will soon grow together.
5. Water well and keep the soil lightly moist for the first few weeks.
6. Mulch thinly with gravel or fine compost; a thick layer of bark chips is not needed.

Care

Watering

Water in dry spells after planting. Once established, extra water is only needed in long droughts, and always in pots.

Feeding

Needs little: a thin layer of compost in April is enough. Too much fertiliser gives soft leaves and fewer flowers.

Marking

Put a cane or label next to the plant in winter: it only reappears in late May and is easily forgotten or dug up.

Spread

In spring, cut off runners that spread too far with a spade.

Deadheading

Not needed: it keeps flowering by itself until the first frosts.

Tip: Plant small spring bulbs such as crocuses or grape hyacinths between the clumps: they fill the space in spring, and by the time their leaves die down, the plumbago takes over.

Hardy plumbago: when to prune it?

Pruning months: March.

When: In March, before the new shoots appear. Leave the old stems standing all winter.

How:

• Cut all old, woody stems back to just above the ground, or to a few centimetres.
• Clear dead bits and fallen leaves from the clump so the new shoots get light.
• No pruning is needed in summer.

Caution: Don’t panic if there is nothing to see in April: the new shoots often only appear in May.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Division

In April–May, cut a piece with roots and runners from the edge of the clump with a spade and replant it straight away.

Softwood cuttings

In June–July, take 5–8 cm cuttings from young, non-flowering shoots and root them under plastic in moist cutting compost.

Runners

In spring, detach rooted runners at the edge and pot them up.

Hardy plumbago: how does it get through the winter?

Hardy to −20 °C.

• Hardy to about −20 °C: no protection is needed in most Belgian gardens.
• Wet soil in winter is more dangerous than frost: make sure drainage is good.
• Leave the old stems as natural protection and only cut them back in March.
• In a pot: stand it in a sheltered spot against a wall and wrap it in hessian or bubble wrap in hard frost.

Diseases and pests

• Late emergence: Not a problem but a trait: the plant only comes up in May. Mark the spot so you don’t dig it up.
• Root rot: The plant disappears after a wet winter, especially on heavy clay. Plant in a well-drained or raised spot.
• Powdery mildew: White powder on the leaves in hot, dry summers. Give plants space and cut off affected leaves; so late in the season it is usually harmless.
• Few flowers: Too much shade or too much fertiliser. Move it to a sunnier spot and feed less.

Through the year

• January: Rest. Leave the old stems standing.
• March: Cut old stems back to just above the ground.
• April: Planting. A thin layer of compost.
• May: New shoots appear. Plant or divide.
• June: Take softwood cuttings. Water in dry spells.
• July: Water during prolonged drought.
• August: Flowering begins. Bees and butterflies visit.
• September: Full flower; the leaves start to turn red.
• October: Blue flowers and red autumn leaves together.
• November: Leave the stems standing as winter protection.

Good for wildlife

Bees

Nectar and pollen for honeybees and wild bees.

Butterflies

Nectar for butterflies.

Did you know?

• The family name Plumbaginaceae comes from the Latin plumbum, lead, which is also where the Dutch name loodkruid (lead herb) comes from.
• Ceratostigma means horned stigma: the stigma of the flower carries small, horn-like outgrowths.
• It is related to the well-known blue Cape leadwort grown in pots, but unlike that tender plant it survives our winters outdoors.