Reed sweet-grass

How to recognise it

Growth habit

Perennial grass, 1–2.5 m tall, which forms large, dense stands on the bank and in shallow water thanks to its creeping rhizomes.

Leaf

Long and strap-shaped, 30–60 cm long and 1–2 cm wide, glossy fresh green with a rough edge and a clear midrib. Where the blade bends away from the sheath there are often two small brownish marks.

Flower

Large, loose and much-branched panicle of 15–40 cm, with numerous green to purplish spikelets of 5–12 mm, from June to August. Wind-pollinated.

Stem

Sturdy, upright and smooth, with closed leaf sheaths; in water often lying flat at first and rooting at the nodes.

Roots

Thick, creeping rhizomes in the mud, which spread a good deal further every year.

Confusion with

Common reed has blue-green leaves with a ring of hairs at the base of the blade and a fluffy, purple-brown plume that only flowers from August. Reed canary-grass has dull blue-green leaves and a dense, lobed flower head. Reed sweet-grass has glossy, fresh green leaves and an open, green panicle from June.

Flowering: June–August · Pruning: February–March

Why grow it?

• Dense marginal growth where moorhens and ducks shelter and nest, and where frogs and newts find cover.
• The seeds feed ducks and other waterbirds in late summer.
• The leaves feed the caterpillars of several moths.
• The creeping rhizomes hold the bank together and slow down erosion.
• It takes up a lot of nutrients from the water and is therefore sometimes used in planted filter beds.
• Decorative from June to August, with flower heads that sway in the wind and leaves that turn straw-yellow in autumn.

Reed sweet-grass: where does it grow best?

• In the wild along ditches, streams, rivers and canals, in marshes, reed beds and wet hay meadows that flood in winter.
• It loves nutrient-rich water and mud: where a lot of fertiliser ends up in the water, it becomes very dominant.
• Sun to partial shade; on a wet, muddy bank or in shallow water up to about 20–30 cm deep.
• In the garden only suitable for a large pond, wildlife pond or wet area; in a smaller pond, grow it in a sturdy planting basket.
• It tolerates changing water levels and a bank that dries out for a while in summer.

Goes well with

• Yellow iris: Yellow flowers in May–June among the fresh green leaves, on the same wet bank.
• Purple loosestrife: Purple spikes in summer, much visited by bees and butterflies.
• Meadowsweet: Creamy, scented plumes on the wet bank.
• Marsh marigold: Yellow spring flowers at the water’s edge, before the sweet-grass starts growing.
• Water mint: Fragrant, flowers in late summer and attracts many insects.

Reed sweet-grass: when and how to plant it?

1. Buy reed sweet-grass from a nursery that sells water and marginal plants. Never dig up plants from the wild, not even from a ditch.
2. Plant from April to June, when the water warms up: that is when the rhizomes establish fastest.
3. In a small or medium-sized pond, grow it in a sturdy planting basket filled with heavy clay or aquatic compost, topped with gravel, so that the rhizomes cannot spread through the whole pond.
4. Place the plant in the marginal zone, with its base 5–20 cm under water; on a wet bank, simply plant it in the mud.
5. One to three plants are enough for a large pond, at least 1 m apart: they soon close up.
6. You can also sow it: sow fresh seed in autumn on wet, muddy compost and leave the pot outside over winter. Division is much quicker, though.

Care

Water

No extra water needed as long as the base stays wet. If the pond dries out briefly in summer, it survives without problems.

Feeding

Never feed: nutrient-rich water makes it even more rampant and encourages algae.

Spreading

Every one or two years, in autumn, cut back the edges with a sharp spade and remove part of the rhizomes from the pond.

Pond life

Leave removed plants on the bank for a day so that larvae, snails and newts can crawl back into the water. Then put them on the compost heap.

Planting basket

Check every spring whether rhizomes are growing over the edge of the basket and cut them off.

Tip: In a small pond, always grow reed sweet-grass in a sturdy planting basket and cut off any rhizomes that grow over the edge every spring: you get a handsome margin without it taking over the pond.

Pruning and mowing

Pruning months: February–March.

When: From late February to late March, before the new shoots appear.

How:

• Leave the dead stems and flower heads standing all winter: insects overwinter in the hollow stems and birds search them for seeds.
• Cut or mow them in late February or March to just above the water line.
• Remove the cuttings so they do not rot in the pond and enrich the water.
• On a long bank, preferably cut in sections: one part this year, another part next year, so there is always some shelter.

Caution: Do not work on the bank from March to July, when waterbirds are nesting and frogs and toads are spawning.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Division

In April–May, cut off a piece of rhizome with a few shoots using a spade and plant it in mud or a planting basket. It almost always takes.

Seed

Sow fresh seed in autumn on wet, muddy compost and leave it outside over winter. It germinates in spring.

Reed sweet-grass: how does it get through the winter?

Hardy to −30 °C.

• The leaves die back in autumn and turn straw-yellow; the rhizomes overwinter safely in the mud.
• Fully hardy, even when the water freezes over.
• The standing stems shelter overwintering insects and spiders.
• From March, the fresh green new shoots grow quickly.

Diseases and pests

• Spreading: In a small pond it fills everything within a few years. Use a planting basket and thin it out every year.
• Ditch closing up: In a ditch it can hinder the flow of water. Clear the ditch in autumn, but only one section at a time, so that animals can move elsewhere.
• Aphids: Sometimes on young shoots in May–June. Birds and ladybirds deal with them; never spray in or near water.
• Dark streaks: Long, dark streaks on the leaves are usually a smut fungus. Not serious: cut off badly affected leaves and leave the rest.

Through the year

• February: Cut old stems back to just above the water line.
• March: Last chance to remove old stems. The new shoots appear.
• April: Plant or divide. Check planting baskets.
• May: Rapid growth. Waterbirds nest in the dense growth.
• June: Flowering begins: the flower heads appear.
• July: Full flower. Do not work on the bank during the nesting season.
• August: The seeds ripen. Ducks feed on them.
• September: Cut back the edges and remove part of the rhizomes from the pond.
• October: The leaves turn yellow. Leave removed plants on the bank for a day.
• November: Leave the stems standing for insects.
• December: Rest. Hardy, even in frozen water.

Did you know?

• Glyceria comes from the Greek glykeros, sweet: the seeds of related species taste sweetish. Those of floating sweet-grass were once harvested and eaten in Eastern Europe as ‘manna’.
• In North America, Australia and New Zealand, reed sweet-grass is an introduced species that overruns marshes and ditches; there it is controlled as an invasive plant.
• There is a variegated form with cream-yellow striped leaves, which grows a little less vigorously and is often sold as a pond plant.