How to Grow Giant Rhubarb
Gunnera manicata
Gunnera manicata produces the largest leaves of any hardy plant in UK gardens, creating a dramatic tropical effect beside ponds and streams. Plant in rich, permanently moist soil in sun or partial shade. Protect the crown in winter by folding the dying leaves over it and adding a thick mulch of straw — the crown is vulnerable to hard frost.
Yearly Lifecycle
Care Essentials
Feed generously in spring with well-rotted manure or compost. These are hungry plants that need rich soil to produce their enormous leaves.
Watch For
- Slugs on emerging shoots in spring
- Crown rot if winter protection is inadequate
- Wind damage to large leaves
Track your Giant Rhubarb care schedule — pruning, feeding, and seasonal tasks
Start planning freeCare Requirements
☀️ Light
Full sun to partial shade
Grows well in sun or partial shade. In hot sunny spots, the large leaves may scorch at the edges during drought — consistent moisture prevents this.
💧 Watering
Constantly moist to boggy soil essential
Never allow the root zone to dry out. Ideal beside ponds or streams. In drier positions, water very generously and mulch thickly to retain moisture.
🌱 Fertilizing
Generous annual feed with well-rotted manure
Apply a thick mulch of well-rotted farmyard manure or compost in spring as growth begins. These are large, hungry plants that need rich soil to reach their potential.
✂️ Pruning
Cut all foliage back in late autumn
After the first frosts blacken the leaves, cut them back and fold them over the crown as insulation. Remove remaining dead stems in early spring before new growth emerges.
❄️ Overwintering
Crown must be protected from frost
Fold cut leaves back over the crown and cover with a thick layer of straw or bracken. In very cold areas, add an extra layer of fleece or hessian. Without protection, hard frost can kill the crown.
Growing Tips
Position beside water
Gunnera needs permanently moist to boggy soil. The ideal position is at the edge of a pond, stream, or bog garden where the roots can reach constant moisture.
Winter crown protection is critical
The crown is frost-sensitive. After the first hard frost blackens the leaves, cut them and fold them back over the crown, then add a thick layer of straw or bracken. Without this, the crown may be killed in a hard winter.
Feed generously in spring
These are among the most hungry plants in cultivation. An annual top-dressing of well-rotted manure or a thick compost mulch in spring directly fuels the production of those spectacular leaves.
Give it real space
A mature gunnera can spread 3 metres or more. Plant at least 3-4 m from paths, buildings, and other plants. The leaves alone can be over 2 m across and will smother anything underneath.
Pests & Diseases
Pest Slug
Identification: Large irregular holes chewed in emerging shoots and young leaves in spring.
- Apply nematode biological control (Phasmarhabditis hermaphrodita) in moist soil above 5°C.
- Use ferric phosphate slug pellets around emerging shoots.
- Metaldehyde pellets as a last resort — use sparingly near water.
Pest Vine Weevil
Identification: Notched leaf margins; C-shaped white grubs in the root zone causing collapse of young plants.
- Apply Steinernema kraussei nematodes to moist soil in autumn or early spring.
- Imidacloprid drench for container specimens.
Pest Capsid Bug
Identification: Small ragged holes in young leaves that enlarge as leaves grow; distorted new growth.
- Insecticidal soap spray on affected shoots.
- Pyrethrum spray in the evening when bugs are active.
Disease Crown Rot Phytophthora / Pythium spp.
Symptoms: Soft, dark brown rotting at the base of stems; plant fails to emerge in spring or collapses suddenly.
Treatment: No cure once established. Remove affected plant material. Improve drainage if possible.
Prevention: Ensure the crown is never submerged in standing water — boggy but free-draining is ideal. Provide adequate winter insulation to prevent freeze-thaw damage.
Disease Gunnera Mosaic Virus Gunnera mosaic virus
Symptoms: Yellow mosaic or mottling on leaves; stunted, distorted growth.
Treatment: No cure. Remove and destroy infected plants. Control aphids which spread the virus.
Prevention: Buy virus-free stock from reputable sources. Control aphid populations.
Log Giant Rhubarb in your garden — track growth, care, and harvests year after year
Start planning free