Purple loosestrife, Lythrum salicaria, is a tall-growing hardy herbaceous perennial, native to the the British Isles. It thrives in moist soil or in the shallow water at pond margins. Upright stems are clothed with slender light green leaves and topped with long spires made up of numerous rosy-mauve flowers through summer. In autumn, the leaves briefly turn bright shades of red and orange before falling, then through winter the dead vertical woody stems retain their form to create excellent structure in the garden. Purple loosestrife is a fantastic wildlife plant as the flowers are rich in pollen and nectar, and attract bees, butterflies and moths. However, purple loosestrife is likely to self-seed freely and can become invasive.
How to grow purple loosestrife
Plant purple loosestrife in autumn or spring into moist soil or at the pond edge. Remove faded flowers if self-seeding might be a problem and cut back dead stems by early spring. Propagate by seed or division.
Where to grow purple loosestrife
Purple loosestrife suits a naturalistic garden style. This is a moisture-loving plant that either needs a reasonable soil that doesn’t dry out, shallow water at the margins of ponds, or a bog garden. Purple loosestrife grows best in full sun but flowers reasonably well in partial shade.
How to plant purple loosestrife
Purple loosestrife is hardy and can be planted in autumn or spring, or in mild spells during winter. If planting in the shallow water at the edge of a pond or stream, plant into an aquatic planting container (a mesh basket) makes pond management easier in future when it becomes necessary to restrict or divide plants. For planting in ponds, use aquatic planting compost or sieved garden soil that hasn’t been fertilized, otherwise the nutrients would encourage the growth of green algae in pond water.
How to care for purple loosestrife
If planting loosestrife in soil in spring, ensure plants are kept watered for their first growing season until established. Cut back the dead stems of purple loosestrife before new growth emerges.
How to propagate purple loosestrife
Collect seed when brown and ripe, sow immediately into pots of moist compost, or sow where plants are to grow. Or allow plants to self-seed and transplant the young seedlings to their planting position.
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Divide established clumps while dormant, any time from autumn to early spring.
Growing purple loosestrife: problem solving
Purple loosestrife is a trouble-free plant to grow. However, it can self-seed freely and the resulting seedlings can become a nuisance as they soon develop deep roots and need to be dug out, rather than just pulled up. To prevent self-seeding, cut off the faded flower heads before the seed ripens and falls.
Advice on buying purple loosestrife
- Purple loosestrife can be found on sale with herbaceous perennials or in the aquatic plant section of nurseries and garden centres, or from mail order suppliers
- Young plants (plugs) can be bought by mail order from suppliers of UK native (wild) plants