Purple loosestrife

Purple loosestrife: how do you recognise it?

Habit

Upright clump 1–1.2 m tall and about 60 cm wide, with angular stems.

Leaves

Narrow, lance-shaped and stalkless, opposite or in threes; sometimes turning red in autumn.

Flower

Long, slender spikes of many flowers with crinkled petals, from June to September.

Colour

Magenta-pink to purple-pink; varieties also in soft pink or a deeper red-pink.

Roots

A sturdy, woody rootstock that grows larger over the years but does not run.

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

Why grow it?

• Long flowering from June to September, with eye-catching pink spikes.
• A magnet for bees, and also loved by butterflies and bumblebees.
• Native: it suits a wildlife garden and the edge of a pond or rain garden.
• It thrives in wet spots where few other flowering plants do well.
• The stems stand through winter and give insects a place to shelter.

Purple loosestrife: where does it grow best?

• Sun or partial shade; it flowers most freely in full sun.
• Any soil will do: sand, loam, clay or peat, acid to chalky.
• Wet soil: at the pond edge, in a bog garden, a rain garden or a border that never dries out. It also tolerates very shallow water.
• Plant 50–60 cm apart, 3–4 plants per m².

Light

Sun and partial shade

Soil type

Sand, loam, clay or peat

Acidity

Not fussy

Moisture

Wet

Size

1.2 m tall, 0.6 m wide

Hardiness

Hardy (to -30 °C)

Goes well with

• Yellow flag iris: Yellow flowers in May–June and sword-shaped leaves on the same wet bank.
• Meadowsweet: Creamy, scented plumes in summer, also native and fond of wet soil.
• Hemp agrimony: Dusky pink heads in late summer, another butterfly magnet.
• Yellow loosestrife: Yellow flower clusters as a contrast to the pink spikes.
• Ornamental grasses: A calm green backdrop for the bright colour.

Purple 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 poor sandy soil mix in some compost.
3. Set the plant at the same depth as in the pot and firm the soil well.
4. Water in generously and keep the soil wet for the first months.
5. By a pond: plant in the wet margin or in a planting basket with heavy soil, with the base no more than a few centimetres under water.

Care

Water

The soil must never dry out. In an ordinary border, water generously in dry summers.

Feeding

Not needed. Certainly do not feed by a pond: it encourages algae.

Faded spikes

Cut them off in September if you do not want it to self-seed.

Support

Usually not needed. In a windy spot you can hold the clump together with a few canes and string.

Division

Every 4–5 years, when the clump gets too big or flowers less in the centre.

Tip: Leave the stems standing all winter and only cut them down at the end of February. If you do not want seedlings, cut off the faded spikes in September.

Purple loosestrife: when to prune it?

Pruning months: February.

When: At the end of February, just before the new shoots appear. Leave the stems standing all winter.

How:

• Cut all old stems down to just above the ground.
• Leave them until then: hollow stems shelter overwintering insects.
• If you do not want seedlings, cut off the faded spikes in September.
• Broken or diseased stems can simply be cut off at the base in summer.

Caution: It self-seeds in wet soil. Cut the spikes off in time if you do not want that, and weed out seedlings while they are small.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Division

In March–April or in September: cut the clump into pieces with a sharp spade. Old clumps have a woody base that is hard to divide; young clumps are easier.

Cuttings

In April–May: cuttings from young shoots at the base, in wet cutting compost. They root readily.

Seed

In spring on wet soil; it germinates easily and also self-seeds. Named varieties do not come true.

Purple loosestrife: how does it get through the winter?

Hardy to −30 °C.

• Fully hardy, to about −30 °C: no protection is needed.
• The plant dies back above ground and shoots again in spring.
• Leave the stems until the end of February: they are winter quarters for insects and give structure.

Diseases and pests

• Drought: In dry soil it stays small, flowers poorly and the leaves discolour. Move it to a wetter spot or water regularly.
• Leaf beetles: Small beetles and their larvae eat holes in the leaves. They usually do little harm; cut off badly affected stems.
• Aphids: On young shoots in spring. Ladybirds usually clear them; otherwise spray them off with water.
• Too many seedlings: In wet soil many young plants come up. Cut the spikes after flowering and weed seedlings early.

Through the year

• February: Cut old stems down at the end of February.
• March: Plant and divide.
• April: Take cuttings from young shoots. Watch for aphids.
• May: Plant. Keep the soil wet in dry weather.
• June: First flowers. Keep the soil wet.
• July: In full flower. Bees and butterflies.
• August: Flowering. Water if the soil dries out.
• September: Cut faded spikes to prevent self-seeding. Plant or divide.
• October: Plant. Leave the stems standing.
• December: Dormant. The stems stay up for insects.

Good for wildlife

Bees

Nectar and pollen for honeybees and wild bees.

Butterflies

Nectar for butterflies.

Did you know?

• Purple loosestrife has three kinds of flowers, with a short, medium or long style. Charles Darwin studied this in detail.
• A wild bee, Melitta nigricans, collects its pollen almost only from this plant.
• It is native in Europe, but in North America it is a notorious invasive plant that takes over whole marshes.