Bog sage

Bog sage: how do you recognise it?

Habit

Slender, upright perennial, 1.5 m tall and about 60 cm wide, with square stems; spreads by underground runners.

Foliage

Narrow lance-shaped, 5–10 cm long, toothed, fresh green; stays fine and light.

Flower

Sky-blue lipped flowers with a white throat in spikes at the tips of the stems, from August to October.

Colour

A pure, clear blue, rare among perennials in late summer.

Roots

Thin underground runners; over the years they form a large group.

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

Why grow it?

• Sky-blue flowers from August until the first frost, a colour that is rare in late summer.
• Tall and airy: adds height without heaviness.
• Bees and butterflies visit the flowers in late summer and autumn, when little else is in flower.
• Loves moist to wet soil, where many other sages refuse to grow.
• Fits well in naturalistic or prairie-style planting.
• Spreads year after year into a lovely group.

Bog sage: where does it grow best?

• Full sun for the richest flowering; in partial shade it grows taller and floppier.
• Moist, rich loam, clay or peaty soil, acid to neutral.
• Keep the soil moist to wet during growth; in winter, water must not stand.
• A warm, sheltered spot, such as in front of a south-facing wall, helps it survive winter.
• Allow about 60 cm of space per plant.

Light

Sun

Soil type

Loam, clay or peat

Acidity

Acid or neutral

Moisture

Normal or wet

Size

1.5 m tall, 0.6 m wide

Hardiness

Half hardy (to -10 °C): protect it in harsh winters

Goes well with

• Coneflower: Yellow flowers next to the sky-blue spikes: a strong contrast.
• Ornamental grasses: Plumes such as miscanthus bring movement and calm.
• Dahlia: Warm shades that flower in the same late period.
• Michaelmas daisy: Purple and pink flowers that close the season together with the sage.

Bog sage: when and how to plant it?

Plant in May–June.

1. Plant only in May–June, when the last night frosts are over.
2. Dig a hole twice as wide as the root ball and mix in compost.
3. Set the plant at the same depth as in its pot and firm the soil well.
4. Leave 60 cm between plants and plant preferably in groups of three.
5. Water in at once and spread a layer of leaf mould mulch around the base.

Care

Water

Water generously in dry spells: it is a plant of wet soil and the foliage droops in drought.

Feeding

A spadeful of compost or organic fertiliser in spring. No more is needed.

Mulching

A layer of leaf mould in spring keeps the soil moist; extra mulch in autumn for winter.

Support

The slender stems can bend in wind. Plant it among sturdier plants or support it with twiggy branches.

Pinching

In May–June, pinch out the tips for a fuller, more compact plant with more flowers.

Runners

Slice off runners that stray too far in spring and give them away or plant them elsewhere.

Tip: Plant it in May–June in a warm, moist, sheltered spot and cover the roots in November with a thick layer of leaves. As insurance, overwinter a cutting frost-free.

Bog sage: when to prune it?

Pruning months: April–May.

When: In April–May, when you see new shoots at the base; the old stems protect the plant in winter.

How:

• Wait until you see new shoots coming out of the ground, as they appear late.
• Then cut the old stems down to just above the ground.
• In May–June, pinch out the tips of the new shoots for a more compact plant.

Caution: It makes underground runners and can advance a lot in moist soil; slice off runners that stray too far. It is not quite hardy, so protect the roots in winter.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Softwood cuttings

In August–September take cuttings of 8–10 cm from non-flowering tips, remove the lower leaves and insert them in moist cuttings compost. Overwinter them frost-free and in the light.

Division

In April–May, when the new shoots appear, split off a piece with roots and shoots and plant it elsewhere.

Bog sage: how does it get through the winter?

Hardy to −10 °C: protect in harsh winters.

• Not quite hardy: tolerates about −10 °C. In mild winters in a sheltered spot it survives; in hard winters it may be killed.
• Leave the stems standing in winter and cover the soil in November with a thick layer (10–15 cm) of leaves, compost or straw.
• Take cuttings in August–September and overwinter them frost-free and in the light, as a back-up in case the parent plant dies.
• In a pot: bring the pot indoors for winter to a cool, bright, frost-free place and water sparingly.

Diseases and pests

• Frost damage: No shoots in spring. Wait until June before giving up, as it starts late; mulch in autumn prevents much damage.
• Drought: Limp, drooping foliage. Water generously and lay a mulch.
• Flopping stems: Slender stems bend in wind and rain. Plant among other plants, pinch out the tips and support.
• Slugs: Young shoots are nibbled in spring. Pick slugs off in the evening or lay a barrier of coarse sand.
• Aphids: On young shoots and flower buds. Ladybirds often deal with them; otherwise rinse them off with water.

Through the year

• March: Do not prune yet. Leave the winter protection.
• April: New shoots appear. Remove the winter cover. Cut off old stems.
• May: Plant after the last frost. Pinch out the tips.
• June: Plant. Water. Add support.
• July: Water in dry weather.
• August: Flowering starts. Take cuttings.
• September: Full flower. Take cuttings for the winter.
• October: Flowers until the first frost.
• November: Cover thickly with leaves or straw. Put cuttings in a frost-free place.

Good for wildlife

Bees

Nectar and pollen for honeybees and wild bees.

Butterflies

Nectar for butterflies.

Did you know?

• The species name uliginosa comes from the Latin uliginosus, ‘of marshy places’, which suits its love of moist soil.
• It grows naturally in the wet grasslands of Brazil, Uruguay and Argentina.
• It flowers until the first frost, often into October, making it one of the last sages in the garden.