Gunnera manicata: overwintering giant rhubarb in UK and Northern Europe

TL;DR

Gunnera manicata (giant rhubarb) is the most spectacular foliage plant for UK and Northern European gardens. Leaves can reach 2.5 meters. It survives winter outdoors in milder zones (USDA 5-6: southern UK, Belgium, Friesland) with simple frost protection: leaf mould, straw, and shelter. In colder winters (northern UK) keep in pots and move. The plant demands abundant water and semi-shade, but rewards you with foliage drama that stops neighbours in their tracks.

Gunnera manicata: the giant of your garden

Gunnera manicata is no ordinary plant. In one season leaves grow from zero to 2-2.5 meters. Petioles thicken like your arm. This is pure drama-architecture - one plant dominates an entire corner. Perfect for the front yard if you want passersby to stop and ask questions.

Gunnera is a giant rhubarb-like plant from South America. Leaves are heart-shaped, gigantic, with undersides riddled with deep veins. The plant grows from a massive rootstock. In full summer with abundant water, it is relentless.

Frost hardiness: roughly -12°C it can sometimes survive without protection, but frost damage is normal below -10°C. In the UK and Northern Europe you must always provide winter protection for outdoor survival.

Planting Gunnera: location and soil

Light. Semi-shade is ideal. Full sun can cause leaf scorch in hot summers. Under trees, against west-facing walls, or spots with afternoon shade - perfect.

Soil. Gunnera loves moist, organically rich soil. Drought and poor drainage are death. Add generous amounts of compost and leaf mould. If your garden is sandy, mix 40% compost into the planting hole. Heavy clay - work it over, add compost, improve drainage.

Space. A mature Gunnera can spread 2-3 meters wide. Plan accordingly. No narrow border - this plant demands a corner or open view.

Planting time. April-May. They dislike transplanting, so plant in the right spot first. Don't move for 3 weeks after planting.

Summer care: water is life

Gunnera drinks heavily. In dry summers you water daily, sometimes twice. The plant is 90% water. Good rain sorts itself, but drought beyond 5 days stops all growth.

Water trick: Mulch around the base with 5-10 cm leaf mould. This maintains soil moisture and temperature.

Feeding. In June add organic slow-release fertiliser (e.g. blood meal or fish emulsion). Gunnera won't grow hard without feeding. Repeat in July/August.

Weeds and cleanup. Remove dead or yellowed leaves in spring. Gunnera puts all energy into new foliage, so some old leaf litter can stay.

Frost protection: the critical months

This is where many Gunnera growers fail. November-March is the danger period.

Method 1: Leaf mould + straw tent (for outdoor). Late October/early November:

• Cut all leaves back to 10 cm above ground
• Heap leaf mould/compost to 30-40 cm high around the plant
• Cover with straw or wood chips (never plastic - that suffocates)
• Lean branches over for heavy snow protection

Method 2: Pot + move (safer for colder regions). For northern UK:

• Plant in large pot (60+ litres) instead of open ground
• In October move the pot against a warm wall (south-facing greenhouse, garage)
• Cover the pot with leaf mould too
• Water minimally in winter (plant sleeps)
• March/April move back to permanent spot outdoors

Method 3: Combo protection (best results).

• Plant half in ground, half-pot-grown sections lifted
• Root-planted plant in soil, top growing parts in large pot
• Expensive, but works for very cold spots

Recovering from frost damage

Sometimes frost damage still happens. Gunnera usually recovers. In March:

• Remove all dead leaf matter
• Wait until April/May
• New leaves emerge from the central growing point
• By June no one sees the damage

Gunnera in the front yard: design tips

Gunnera is a statement plant. You build the garden around it, not vice versa.

• Place against low wall or corner (gives backdrop)
• Low plants nearby: Hosta, Astilbe, small ferns
• Gravel or pebbles at the base (contrast with giant leaves)
• Lighting: solar lamps for evening silhouette

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Step-by-step: Gunnera manicata overwintering

Step 1: Plant preparation (May-June)

Plant your Gunnera in semi-shade with moist, compost-rich soil. Water well in first weeks.

Step 2: Summer care (June-September)

Water daily in dry spells. Add fertiliser. Let it grow.

Step 3: Autumn prep (October)

Cut all leaves back. Heap leaf mould/compost and straw around plant.

Step 4: Winter watch (November-March)

Monitor frost. Extra straw in extreme cold. Water minimally. Check in February for damage.

Frequently asked questions

Can Gunnera grow in semi-shade?

Yes, even better. Semi-shade prevents leaf scorch. Full shade slows growth, but semi-shade is ideal.

How fast does Gunnera really grow?

In ideal conditions (abundant water, heat, feeding) 10-20 cm per week in summer. By August leaves can reach 1.5-2 meters.

Which Gunnera variety is hardiest?

Gunnera manicata is standard. Gunnera tinctoria is smaller, slightly hardier. Gunnera monostachia very small. For maximum drama: manicata.

Can I move Gunnera?

Bad idea. Deep-rooted, stress-sensitive. Plant on permanent spot and leave it. Moving in pots stresses the plant.

Does Gunnera grow from seed?

Theoretically yes, but seed is rarely available. Much faster: buy young plants (£20-50). Grows to dramatic size in 1-2 seasons.

Plan your exotic garden

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