Giant rhubarb
Gunnera manicata · Gunneraceae
The largest leaves that can be grown outdoors in a temperate garden: puckered, prickly parasols wide enough to shelter under, on thick, spiny stalks.
- Size
- 8 ft tall, 11½ ft wide
- Zones
- 7 to 10
- Light
- Part sun to part shade
- Flowers
- Grown for its leaves; flowers mid June to mid July
- Pets
- Not checked
- Job in a bed
- Specimen
A bed built around giant rhubarb
The planner designed this bed around giant rhubarb when this page was made: a 30 × 14 ft (9.1 × 4.3 m) cottage garden in zone 7, part sun. It chose the other plants from the 376 that suit those conditions and its wet soil, and says below why giant rhubarb stands where it does.
The plants
- 1 Giant rhubarb × 1, dark green leaves
- 2 Mouse-ear coreopsis 'Nana' × 46, yellow
- 3 Blue star creeper × 35, blue
- 4 Paperbush × 1, yellow
- 5 White mugwort × 3, cream
- 6 Joe Pye weed 'Little Joe' × 4, pink
- 7 Garden phlox 'Jeana' × 4, pink
- 8 Canadian burnet × 3, white
- 9 Rose turtlehead × 8, pink
- 10 Woodland phlox × 22, lavender
- 11 Virginia bluebells × 35, blue
- 12 Indian pink × 5, red
- 13 Woodland stonecrop × 63, white
- 14 Camassia × 9, blue
- 15 Double snowdrop × 24, white
Why this plant
- The only plant grown for its leaves. Leaf lasts all season, where a flower lasts a few weeks.
Why here
- Anchors a back corner. At 8 ft it is the tallest plant here, and the tallest close the ends of the bed, where they stand in front of nothing.
- A step in the back row. Next to garden phlox 'Jeana' (4 ft): no two neighbours there are the same height, so the back steps up and down like a skyline.
- One plant, alone. A feature plant is seen as an object, and needs clear ground around it.
Why now
- Here for its leaves, spring to frost. They cover the 10 weeks between early March and late November when nothing on the plan is in flower.
Planned as a cottage garden: 185 of the 230 plants (80%), bulbs aside, stand alone or in groups of no more than five, small enough for the kinds to mingle. Woodland stonecrop is planted in 15 places along the bed, which gives it rhythm. Cool colours (blue, pink and lavender) with yellow and red as the warm notes, and cream and white to calm things between them.
The planner's own design check: 10 Excellent, 6 Good, 1 Satisfactory. It flags one thing to watch: Nothing on this plan is highly poisonous or an aggressive spreader.
Open this bed in the planner Change its size, the sun or the style, move plants about, or swap one for another.
Where giant rhubarb goes in a border
At 8 ft it belongs at the back of a bed. In the planner's ten height classes it is super tall (over 6½ ft).
Its job: specimen. A feature plant with a shape of its own. It stands alone with room around it, and repeats only at a distance.
A plant for a lakeside, not a border. It needs permanently wet soil, shelter from wind, and its crown covered in winter with its own dead leaves. Nothing else gives such scale.
- Lakesides and large ponds
- A jungle effect
- Bog gardens with room
What to plant with giant rhubarb
Plants recorded as good partners for it, and what each pairing does:
- Royal fern: medium leaves against its bold ones; low enough (5 ft) to stand in front of it; happy in the same wet soil.
- Japanese iris: adds the flowers, late June to mid July; medium leaves against its bold ones; low enough (3 ft) to stand in front of it.
- Ostrich fern: medium leaves against its bold ones; low enough (4 ft) to stand in front of it; happy in the same wet soil.
Questions about giant rhubarb
Does giant rhubarb need sun or shade?
Giant rhubarb grows in part sun (4 to 6 hours of sun, including some afternoon sun) and part shade (2 to 4 hours of sun, mostly in the morning).
It wants moist to wet soil, rich in organic matter, and plenty of water.
What zones does giant rhubarb grow in?
USDA zones 7 to 10. It is hardy to zone 7, which means it survives winter nights down to about 10 °F (−12 °C).
Gardening in Canada? Use the USDA zone for your town: Canada's own zone map uses different numbers.
How far apart should giant rhubarb be planted?
10 ft (300 cm) apart, from the middle of one plant to the middle of the next. That is a little closer than its full width of 11½ ft (350 cm), so a group knits into one patch.
It grows 8 ft (250 cm) tall. Give it the full distance from anything taller, or it will lean out towards the light.
How many giant rhubarb plants do I need?
Usually one. At 10 ft (300 cm) across, it is a plant you place, not one you mass. For a hedge or screen, set them 10 ft apart: two plants for a 10 ft run.
In the bed above, the planner used one in one group.
Is there a native plant like giant rhubarb?
Giant rhubarb is not native to North America. These North American natives come closest to doing its job:
- Umbrella plant: the same job in a bed; belongs in the middle, not at the back, 5 ft shorter.
- Hollow Joe-Pye weed: the same job in a bed; 16 in shorter, 6½ ft narrower.
- Purple-stemmed royal fern: the same job in a bed; 4½ ft shorter, 7 ft narrower.
Matched the way the planner's Swap button matches plants: the same job in a bed, then size, then flowering time.
What does giant rhubarb look like in winter?
Giant rhubarb dies down to the ground and there is nothing to see until spring. The old stems can be cut in autumn, or left until spring as shelter for overwintering insects.
In these guides
Every fact on record
- Type
- Perennial
- Size
- 8 ft (250 cm) tall, 11½ ft (350 cm) wide
- Plant
- 10 ft (300 cm) apart
- Height class
- Super tall (over 6½ ft)
- Place in the bed
- Back
- Flowers
- Mid June to mid July; upright spires; green, red
- Leaves
- Bold texture, herbaceous; dark green
- Shape
- Mounding, clumping
- Hardy in
- USDA zones 7 to 10
- Light
- Part sun, part shade
- Soil
- Rich, moist to wet
- Water
- High
- Feeding
- Moderate, in spring
- Family
- Gunneraceae
Not yet checked against an outside reference: its figures rest on general horticultural knowledge. Flowering times are for zone 5: later in colder zones, earlier in warmer ones. Toxicity and spread information is a general gardening guide, not veterinary or medical advice, and invasive status varies by region. If a person or pet eats a plant, contact poison control or a vet. Check your local invasive species list before planting anything with a spread warning.