Giant cowslip

Giant cowslip: how do you recognise it?

Habit

Clump-forming perennial 60–80 cm tall and about 50 cm wide, with a leaf rosette and sturdy, upright flower stems.

Foliage

Oval to broadly oval with a heart-shaped base, 15–30 cm long, toothed edge and long stalks; fresh green, dying back in winter.

Flowers

Umbel of 20–40 nodding, bell-shaped flowers of about 2 cm, from June to August.

Scent

Sweet and strong, especially on calm summer evenings.

Colour

Sulphur yellow; stems and calyces dusted with white or yellow meal. Seedlings may flower orange or red.

Roots

Fibrous and shallow; it needs permanently moist soil and does best with its feet in the water.

Flowering: June–August · Plants: March–April and September–October

Why grow it?

• Flowers from June to August, long after most primulas have finished.
• The yellow bells have a sweet scent, especially in the evening and on still days.
• Bees and bumblebees visit the flowers.
• Imposing in wet ground: stems up to 80 cm and big leaves.
• Fully hardy to about −25 °C and returns every year.
• Self-seeds in moist soil and so forms a natural group.

Giant cowslip: where does it grow best?

• Half shade or light shade; in full sun only if the soil stays wet all the time.
• Wet, humus-rich soil: loam, clay or peat, acid to neutral. Ideal at the edge of a pond or stream, or in a bog garden.
• The soil must never dry out in summer, or the leaves scorch.
• Sheltered from strong wind, which can snap the tall stems.
• Allow 50 cm between plants; in a group of 3–5 you get the finest effect.

Light

Partial shade and shade

Soil type

Loam, clay or peat

Acidity

Acid or neutral

Moisture

Wet

Size

0.8 m tall, 0.5 m wide

Hardiness

Hardy (to -25 °C)

Goes well with

• Rodgersia: Big, hand-shaped leaves and creamy white plumes in the same wet spot.
• Hosta: Large, calm foliage in the same half shade.
• Siberian iris: Slim leaves and blue flowers in early summer.
• Ostrich fern: Fresh green, elegant fronds next to the primula.
• Astilbe: Pink and red plumes in the same damp, half-shaded spot.

Giant cowslip: when and how to plant it?

Plant in March–April and September–October.

1. Plant in March–April or in September–October, when the soil is moist but not frozen.
2. Dig a generous hole and mix in plenty of compost or leaf mould so that the soil holds moisture.
3. Set the plant at the same depth as in its pot, with the centre of the rosette at soil level.
4. Plant in groups of 3–5, 50 cm apart.
5. Water in generously straight away and keep the soil constantly moist in the first year.
6. Spread a layer of leaf mould around the plants as mulch, without covering the crown.

Care

Water

Keep the soil moist at all times, especially while in flower. In an ordinary border water generously and regularly in dry weather; beside a pond or in a bog garden this is rarely necessary.

Feeding

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

Mulching

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

Spent flowers

Cut the stems down after flowering. Leave them if you want seedlings.

Tidying

Remove dead leaves in February–March so the new rosettes get light.

Slugs

Watch for slugs in spring: they love the young leaves.

Tip: It belongs at the edge of a pond or stream, where the soil stays wet all the time: there it grows strongly and self-seeds. Do not plant it in a dry spot.

Giant cowslip: when to prune it?

When: It is not pruned. Cut off spent flower stems after flowering and remove dead leaves in February–March.

How:

• Cut spent flower stems down to the base if you do not want it to self-seed.
• Leave a few stems until the seed capsules are brown and dry if you want seed.
• Pull or cut off dead, brown leaves in February–March, taking care not to damage the centre of the rosette.

Pruning calendar and basic rules

Propagation

Seed

Sow fresh seed in autumn or early spring in a tray of seed compost, without covering it: it germinates in light. Put the tray outside in the cold and keep it moist. Seedlings do not always resemble the parent plant and may flower orange or red.

Division

Divide older clumps in September, after flowering, or in early spring. Split them into pieces with roots and a bit of rosette and replant them straight away in moist soil.

Giant cowslip: how does it get through the winter?

Hardy to −25 °C.

• Fully hardy, to about −25 °C: no protection is needed in Belgian winters.
• The foliage dies back. Leave it in place until spring as protection for the rosettes.
• Wet soil in winter is not a problem; a dry summer is far more dangerous.

Diseases and pests

• Slugs: Holes in the young leaves in spring. Collect them in the evening and clear hiding places such as piles of dead leaves.
• Drought stress: Limp leaves with brown, dry edges. Water generously, lay a thick mulch and, if necessary, move it to a damper spot.
• Vine weevil: The grubs eat the roots, especially in pots, and the plant suddenly wilts. Use nematodes against the grubs.
• Too many seedlings: In wet soil it self-seeds abundantly. Pull up the young plants or cut off the seed heads before they ripen.

Through the year

• February: Remove last year’s dead leaves.
• March: Plant or divide. Give compost. Watch for slugs.
• April: Plant. Apply mulch. Keep the soil moist.
• May: Keep the soil moist. Watch for slugs.
• June: Flowering begins. Water generously in dry weather.
• July: Full flower and scent. Water in dry weather.
• August: Last flowers. Cut off seed heads or let them ripen.
• September: Divide after flowering. Plant. Sow.
• October: Plant. Mulch with leaf mould.

Good for wildlife

Bees

Nectar and pollen for honeybees and wild bees.

Did you know?

• The plant was discovered in 1924 by Frank Kingdon-Ward in Tibet and named after his wife Florinda.
• Stems and calyces are dusted with a white to yellow powder that botanists call meal.
• Unlike most primulas, it flowers only in summer, from June to August.