Yellow loosestrife

Yellow loosestrife: how do you recognise it?

Habit

Upright, sparingly branched stems of 0.6–1 m, from a creeping rootstock with runners.

Leaves

Lance-shaped, 5–12 cm, opposite or in whorls of three or four, with tiny black or orange gland dots that you see against the light.

Flower

Bright yellow, star-shaped, 1.5–2 cm, with five petals, in sprays at the stem tips, from June to August.

Oil

The flowers produce no nectar, but oil and pollen: a reward for specialised bees.

Roots

Creeping rootstock with underground runners; after a few years it forms a sizeable patch.

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

Why grow it?

• Bright yellow flower sprays from June to August, a vivid colour by the water.
• Essential for the yellow loosestrife bee, a wild bee that collects oil and pollen from the flowers.
• Other bees and hoverflies also visit the flowers for pollen.
• It grows in wet soil and along pond edges, where many garden plants rot.
• Native, tough and very hardy.
• The stems give insects shelter in winter.

Yellow loosestrife: where does it grow best?

• Sun or partial shade; it flowers best in sun.
• Wet to very moist soil: sand, loam, clay or peat, acid to chalky. It copes well with temporary flooding.
• Ideal on a wet bank or in the marsh zone of a pond, down to about 5 cm under water.
• Give it room: allow 60 cm per plant and, in a small garden, plant it with a root barrier or in an aquatic basket.
• For the loosestrife bee: plant a group in a sunny spot, with some bare ground nearby where it can nest.

Light

Sun and partial shade

Soil type

Sand, loam, clay or peat

Acidity

Not fussy

Moisture

Wet

Size

1 m tall, 0.6 m wide

Hardiness

Hardy (to -30 °C)

Goes well with

• Purple loosestrife: Purple spikes next to the yellow: a classic waterside pairing.
• Hemp agrimony: Pink flower heads in late summer, as the loosestrife finishes.
• Meadowsweet: Creamy, scented plumes in the same wet spot.
• Yellow flag iris: Yellow flowers in May–June, before the loosestrife starts.
• Water mint: A low, scented plant for the base, in the same wet soil.

Yellow loosestrife: when and how to plant it?

Plant in March–May and September–October.

1. Plant in March–May or in September–October.
2. Dig a hole twice as wide as the root ball; in a small garden, surround it with a root barrier or a bottomless bucket.
3. Plant at the same depth as in the pot and firm the soil. In the pond, use a basket of heavy soil topped with gravel, 0–5 cm under water.
4. Leave about 60 cm between plants.
5. Water in well and keep the soil wet until the plant has established.

Care

Water

The soil must stay wet; water in dry summers or top up the pond with rainwater.

Feeding

Not needed; in a pond, fertiliser only feeds algae.

Keeping in check

Every spring, chop off runners that stray beyond where you want it.

Support

Usually not needed; in a windy spot the stems may flop.

Stems

Leave the faded stems over winter and cut them down in March.

Tip: Plant a group of at least three in a sunny spot: the more flowers, the better the chance that the loosestrife bee finds your garden. Leave the stems standing over winter.

Yellow loosestrife: when to prune it?

Pruning months: March.

When: Cut the dead stems down in March, just before the new shoots appear.

How:

• Cut all old stems down to just above the ground.
• Leave the stems until then: insects shelter in them over winter.
• Faded flower sprays can stay; there is no need to cut them off.
• While tidying, chop off any runners that have spread too far.

Caution: Do not leave pieces of rootstock lying around: every piece can grow into a new plant.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Division

In March–April or in October, chop off a piece of the clump with rootstock and buds and replant it elsewhere.

Runners

In spring, detach runners with a few buds and plant them straight away or pot them up.

Seed

Sow fresh seed in autumn in a pot of moist seed compost and leave it outside over winter; keep the pot wet.

Yellow loosestrife: how does it get through the winter?

Hardy to −30 °C.

• Very hardy, to about −30 °C: no protection needed.
• The top growth dies back; the rootstock regrows in spring.
• Leave the stems over winter: they shelter insects and decorate the bank.
• An aquatic basket can simply stay in the water.

Diseases and pests

• Spreading: Runners pop up among other plants. Chop them off every spring and grow the plant in a basket or with a root barrier.
• Aphids: On the shoot tips in spring. Hose them off; do not use pesticides near the pond.
• Slugs: Young shoots are eaten in April–May. Pick them off in the evening; older plants are hardly bothered.
• Few flowers: Too much shade or soil that is too dry. A sunnier, wetter spot helps.

Through the year

• March: Cut down old stems. Plant or divide.
• April: Plant. Chop off runners that spread too far.
• May: Plant. Watch out for slugs.
• June: First yellow flowers.
• July: Full flower. The loosestrife bee is on the wing, collecting oil and pollen.
• August: Last flowers. Water or top up the pond in dry spells.
• September: Plant or divide.
• October: Plant. Leave the stems standing.
• December: Resting. The stems decorate the bank.

Good for wildlife

Bees

Nectar and pollen for honeybees and wild bees.

Did you know?

• The yellow loosestrife bee collects oil from the flowers: it uses it to waterproof its nest cells and mixes it with pollen as food for its larvae.
• In Dutch the bee is called slobkousbij, gaiter bee, after the dense hairs on the females’ hind legs, which carry the oil and pollen.
• Its English name loosestrife is shared with purple loosestrife, but the two plants are not related.