Pampas grass

About

Pampas grass gets bigger than anybody expects and cuts you when you deal with it.

The plumes are spectacular. Silvery-cream feathered heads up to a metre long, held 2 to 3 m above the ground from late August, standing through the winter and catching the light on a frosty morning.

The plant beneath them is a fountain of arching evergreen leaves that reaches 1.5 m tall and 2 m across within a few years, and a mature clump on a small front lawn is out of scale with everything around it. Most of the pampas grass that gets dug out of British gardens was planted somewhere it could not fit.

The leaves are the other issue. The margins carry fine serrations that work like a saw, and a hand drawn along one produces a deep clean cut. Cutting the clump back is a job for gauntlets, long sleeves and eye protection.

Its reputation as a 1970s suburban cliche has kept it out of fashion for decades, and the grass itself is a fine plant used properly. Given space, sun and free drainage it is architectural, needs almost nothing, and stands through the winter when the rest of a border has gone.

Only female plants produce the full showy plumes, which is worth knowing before buying an unnamed one.

Appearance and character

An evergreen perennial grass forming a dense clump with foliage at 1.5 m and flower stems reaching 2 to 3 m.

Leaves are long, narrow, arching, blue-green to grey-green, up to 2 m long, with margins carrying fine sharp serrations along their whole length.

The clump builds outwards from the centre and reaches 2 m across in five years, with a dense mass of old leaf bases at the base.

Plumes appear from late August into September, 30 cm to 1 m long, dense and feathered, held on stiff upright stems well clear of the foliage.

Colour runs from silvery-white through cream to pale pink in the cultivar ‘Rosea’.

Female plumes are the showy ones. Male plumes are narrower, thinner and duller, since they carry no silky hairs on the florets, and an unnamed seed-raised plant may turn out to be male.

The plumes stand through the winter and gradually shed, and they dry well for indoor arrangements if cut before they are fully ripe.

‘Pumila’ is the compact cultivar at 1.2 to 1.5 m, and it is the right choice for most gardens.

Where it is from

Southern South America, from Argentina, southern Brazil, Uruguay and Chile, growing on the pampas grassland and along river margins.

It was introduced to Europe in the 1840s and became fashionable in Victorian gardens, and it had a second wave of popularity in Britain in the 1960s and 1970s.

The plant is invasive in a number of countries with suitable climates. It is a declared weed in parts of California, Australia, New Zealand, South Africa and Spain, where it colonises coastal ground, roadsides and disturbed land in enormous numbers.

Seed production is prolific. A single female plume can carry over a hundred thousand seeds, carried on the wind for many kilometres.

Britain has not seen the same problem, because the climate limits seed ripening in most of the country, and it has naturalised locally in mild coastal areas of the south and west. Anyone gardening near the coast is worth deadheading the plumes before they shed.

The name comes from the Spanish cortar, to cut, describing the leaf edges.

A persistent urban legend that pampas grass in a front garden signals something about the householders has no basis whatever and is worth mentioning only because people ask.

How it grows

Plant in spring rather than autumn, which gives it a full season to establish before facing a wet winter.

Choose full sun and free-draining soil. It flowers poorly in shade and the crown rots in cold wet clay.

Improve drainage on heavy ground with grit, or plant on a slight mound.

Allow the space it will need, which is 2 to 3 m across for the full-sized plant and 1.5 m for ‘Pumila’. Underestimating this is the commonest mistake.

Keep it away from paths, doorways, seats and anywhere children play, because of the leaf edges.

Water through the first summer and after that leave it alone.

Cut it back in late winter, in February or early March, before the new growth starts. Cut the whole clump down to 30 cm with shears, a hedge trimmer or a pruning saw.

Wear gauntlets, long sleeves, stout trousers and eye protection. This is not optional advice.

Comb out the dead material from the base with a gloved hand or a rake afterwards, which tidies the clump and lets light in.

Do not burn it in situ. This was traditional advice, it damages the crown, and it is a real fire risk since dry pampas grass burns fiercely and fast.

Deadhead the plumes in a mild coastal garden before they shed, which stops it seeding into the wild.

Divide only if you must, in spring, and be aware that an established clump is extremely tough and may need an axe or a mattock.

Buy a named female cultivar rather than an unnamed seedling, which may turn out to be male with poor plumes.

Through the seasons

Winter the plumes stand through the season and are at their best under frost, and the foliage remains evergreen.

Spring is cutting-back time in February or early March, followed by fresh growth from April.

Summer builds the clump, and the plumes start to emerge in late August.

Autumn is the peak, with the plumes fully out from September and holding through the autumn.

Care difficulty

Easy in the right place.

It needs no feeding, no watering once established, no staking and no pest control, and it lives for decades.

The two difficulties are both about the gardener rather than the plant. Giving it enough room, and cutting it back once a year while properly protected.

Crown rot in cold wet clay is the only cultural failure worth mentioning, and it is a drainage problem.

Watering

Water through the first summer after planting.

Established pampas grass needs no watering in Britain and tolerates drought well.

It dislikes waterlogged ground far more than dry, so improve drainage rather than adding water.

Mulch lightly in spring with compost if the soil is poor, keeping it clear of the crown.

Warning signs, diseases and pests

A clump that has grown far larger than expected is normal, and it is the commonest complaint. Plant ‘Pumila’ next time and allow 2 to 3 m for the full-sized plant.

Thin dull narrow plumes is a male plant. Only female plants produce the full silky display. Buy a named female cultivar.

No plumes at all is usually shade, a plant that is still too young, or cutting back too late in spring and removing the developing growth.

A dead brown centre with growth only around the edges is a congested old clump. Cut it hard back in late winter and comb out the dead material, or divide it.

The crown failing to grow away in spring after a wet winter is rot. Improve drainage and plant on a mound.

Seedlings appearing around the garden or on nearby waste ground is the plant seeding, which matters most in mild coastal areas. Deadhead the plumes before they shed.

There are almost no pests or diseases worth mentioning.

Growing environment

Full sun. It flowers poorly in shade.

Free-draining, reasonably fertile soil. Improve heavy clay with grit and avoid ground that waterlogs.

Fully hardy in most of Britain, and it does best in the milder south and west and along the coast, where it also tolerates salt wind well.

Allow 2 to 3 m of space for the species and 1.5 m for ‘Pumila’.

It suits a large lawn as a specimen, a big gravel garden, a coastal garden, a border back, a screen or a modern architectural planting.

Do not plant it beside a path, a door, a seat or a play area, and do not plant a full-sized one in a small front garden.

Grow it with plants of a similar scale. Phormium, yucca, large ornamental grasses, kniphofia and eryngium all sit comfortably with it and want the same free-draining sunny conditions.

Deadhead in a mild coastal garden to stop it seeding into surrounding land.

Its wildlife value is fair. The dense evergreen clump gives good winter shelter for insects and small mammals, and the plumes are used as nesting material by birds.

Feeding

None needed on reasonable soil.

Feed once in spring with a balanced general fertiliser on poor sandy ground.

Mulch lightly with compost in spring, keeping it clear of the crown.

Avoid high-nitrogen feeds, which give soft leafy growth and fewer plumes.

A plant without plumes is short of sun or is male rather than short of nutrients.

Troubleshooting

When do I cut it back? February or early March, before the new growth starts. Cut the whole clump to 30 cm and comb out the dead material from the base.

Should I burn it off? No. The old advice to set fire to it damages the crown and is a real fire hazard, since dry pampas grass burns fiercely and fast.

How do I cut it without getting cut? Gauntlets, long sleeves, stout trousers and eye protection, without exception. The leaf margins are serrated and produce deep clean cuts, and eye injuries have occurred.

My plumes are thin and dull. You have a male plant. Only female plants produce the full silky plumes. Buy a named female cultivar rather than an unnamed seedling.

How big does it get? Two to three metres across and 2 to 3 m tall in flower for the full sized plant. ‘Pumila’ reaches about 1.5 m and is the right choice for most gardens.

It has no plumes. Too much shade, a plant that is still young, or cutting back too late in spring. Move it into full sun and cut it back in February.

Is it invasive? Seriously so in California, Australia, New Zealand, South Africa and Spain. In Britain the climate limits it and it has naturalised locally in mild coastal areas. Deadhead the plumes if you garden near the coast.

Can I dry the plumes? Yes. Cut them before they are fully ripe, in early autumn, and hang them upside down somewhere dry and airy.

It has died out in the middle. A congested old clump. Cut it hard back in late winter and comb out the dead material, or divide it, which takes a mattock on an established plant.