Vegetable · Polygonaceae
Rhubarb
Rheum rhabarbarum
Thick red-and-green stalks rise in a spring clump beneath broad, spreading leaves, the tart part you cook and the big blades you cut away.
Full sun
Every 5–10 days
365–730 days
USDA 3–8
Overview
Rhubarb sends up a clump of thick, upright stalks in shades of red and green, and those tart stalks are what cooks turn into pies, crumbles, and jam, the source of the old name pie plant. It sits in the knotweed family. Above the stalks the plant carries broad leaf blades, and the whole clump shrugs off winters as cold as -40°F (-40°C).
Each spring the same crown pushes a fresh flush of stalks straight up from the ground, a long-lived perennial clump that returns for a decade or more before it grows congested and needs splitting. The first year's stalks are left standing, the second year's picked sparingly, and from the third year the clump fills out enough to harvest in full.
Each stalk is topped by a large, broad leaf blade, and it is the blade, not the stalk, that is dangerous. Those blades are loaded with oxalic acid and toxic to people and animals, so they are cut away from the stalks and thrown out. Handle the plant by that rule and the rest of it is easy.
Care
The short version: rhubarb wants full sun, deep and fertile soil, and about an inch of water a week to swell its thick stalks. Feed it in early spring as the crown wakes, mulch to keep the crown cool, and divide the congested clump every few years so the stalks stay stout.
Light
Rhubarb colors and thickens best in full sun, though it holds up in partial shade where summers run warm. The more light the clump takes, the stouter and more plentiful the stalks stand.
Water
Rhubarb needs soil that stays evenly moist but never waterlogged, about an inch (2.5 cm) of water a week to keep the stalks swelling. Water more deeply through hot, dry spells, and lay a thick organic mulch over the crown to hold moisture and keep it cool.
Soil
Rhubarb roots into deep, fertile, well-drained loam worked full of organic matter. A pH of 6.0 to 6.8 suits it, and sharp drainage matters most, since a crown sitting in wet soil turns soft and rots.
Temperature
Rhubarb is a cold-country plant that takes -40°F to 86°F (-40°C to 30°C). It needs a real winter chill to die back and push up strong again, and it flags where the summer heat drags on.
Humidity
Ordinary outdoor humidity of 40% to 60% is all the clump needs. Air moving through the broad leaves matters more, since foliage left crowded and damp breaks out in leaf spot.
Feeding
Feed rhubarb once in early spring as the crown breaks dormancy, with a balanced fertilizer or well-composted manure. The clump feeds heavily, so rich soil and that yearly feeding are what pack thickness into the stalks.
Pruning
When a stout central flower stalk rises from the clump, cut it at the base, or the plant pours its strength into seed instead of stalks. Strip off any dead, yellowing, or frost-damaged leaves, and throw the toxic blades out rather than feed them to animals.
Repotting
Rhubarb keeps to the ground, but the crown wants dividing every 5 to 10 years as it grows congested. Thin, spindly stalks or a clump gone hollow and dead at the center are the signs to lift it, split it, and replant the firmest pieces.
Size & spacing
A full clump stands 2 to 4 feet (60 to 120 cm) tall and spreads about as wide, so give each crown 3 to 4 feet (90 to 120 cm). The broad leaves need that width for air to pass and for the stalks to reach full size.
When to plant
Rhubarb is timed by the cold. Set dormant crowns out in early spring as soon as the soil can be worked, and leave the first flush of stalks unpicked while the roots thicken. Stalks push up from spring into early summer, reaching a full harvest from the third year onward.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Sow: start seed indoors 8-10 weeks before the last spring frost (seed-grown plants are slow and variable)
- Plant: set out dormant crowns in early spring as soon as the soil can be worked (fall planting also works in mild areas)
- Harvest: harvest stalks in spring through early summer; do not harvest the first year, take only a few stalks the second year, and harvest fully from the third year onward
Hardiness
USDA hardiness zones: 3–8
Temperature: down to -40°C
Troubleshooting
Rhubarb is sturdy, and its troubles show plainly in the stalks and leaves: a thinning clump, a discolored crown, or a stalk that shoots up and flowers. A close look tells you which one you are facing. Match the symptom below and act before the clump weakens.
A crown gone soft, brown, and mushy
A crown that has turned soft, brown, and mushy is suffering crown rot, usually from soil that stays waterlogged and sometimes a fungus such as Phytophthora. Rotted tissue is past saving, so dig the crown out and destroy it. Replant firm, healthy divisions on a raised, well-drained spot, and keep mulch off the crown itself.
Fix:
- Remove and destroy affected crowns
- Improve drainage and replant healthy divisions on a raised, well-drained site
A stout flower stalk rising above the clump
The thick central stalk topped with creamy, greenish-white flower heads is bolting, the plant setting seed as summer heats up or the crown grows old and congested. It pulls strength from the leaf stalks, so cut it at its base as soon as it rises. Keep the clump watered and mulched, and split old crowns to keep it from returning next year.
Fix:
- Cut the flower stalk off at its base as soon as it is seen
- Keep plants consistently watered and mulched
Stalks rising thin, short, and spindly
Stalks that come up thin and spindly point to an overcrowded crown that has grown too congested, with lean soil and heavy picking making it worse. Lift and split the crown in early spring, replant the firmest pieces, and top-dress with compost or a nitrogen-rich fertilizer. Ease off harvesting for a season so the clump can thicken again.
Fix:
- Divide the crown in early spring and replant vigorous pieces
- Top-dress with compost or a nitrogen-rich fertilizer
- Reduce or stop harvesting for a season to let the plant recover
Spotted or hole-punched leaf blades
Round tan-to-purple spots with clean margins mark a fungal leaf spot such as Ascochyta or Ramularia, while ragged, chewed holes come from slugs or the rhubarb curculio. Pull off the worst-marked blades and destroy them, open the clump so air moves through, and water at the base. Hand-pick the beetles and keep after the slugs.
Fix:
- Remove and destroy badly affected leaves
- Improve air circulation and avoid overhead watering
- Hand-pick beetles and manage slugs
Toxicity
Rhubarb splits cleanly into two parts, and the eye can tell them apart. The thick cooked stalks are safe to eat, but the large leaf blades hold oxalic acid and anthraquinone glycosides that are toxic to people, cats, dogs, horses, and livestock. Cut the blades from the stalks, dispose of them out of reach, and keep trimmings away from pets and grazing stock.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds
Safe for
People
Cats Moderate
A cat that bites into a leaf blade drools and paws at its stinging mouth, then vomits and goes limp and quiet. A larger mouthful is worse, since the oxalates can set off tremors and strain the kidneys.
Dogs Moderate
A dog that chews the broad leaves drools, turns queasy, loses its appetite, and sinks into a dull, sluggish rest. Enough of the same crystals can bring on tremors and kidney damage.
Horses Moderate
The blades sting a horse's mouth and bring on heavy, ropey drooling, colic-like cramping, and weakness. A large feed risks lasting kidney harm, so horses are fenced clear of the foliage.
Rabbits Toxic
The oxalic acid packed in the leaves is genuinely dangerous to rabbits, with no safe amount. Every blade and trimming is kept well out of their reach.
Livestock Toxic
Cattle, sheep, and goats that graze the leaves can fall into severe oxalate poisoning, drooling, cramping in the gut, staggering, and failing at the kidneys. Leaf trimmings are never tossed into a pasture or pen.
Birds Toxic
The oxalic acid and anthraquinone compounds in the blades make them unsafe for poultry and pet birds alike. Backyard hens are kept from scratching through discarded leaves.
People Stalks safe
The cooked stalks are a safe, long-loved food, but the broad leaf blades are not. They carry oxalic acid that burns the mouth and brings nausea and vomiting, so the blades are trimmed off and thrown away.
The red or green leaf STALKS (petioles) are safe to eat when cooked, but the large LEAF BLADES are toxic to pets and people and must never be eaten or fed to animals. Cut blades off and dispose of them; do not leave trimmed leaves where pets or livestock can reach them.
Helpline numbers
United States
ASPCA Animal Poison Control: (888) 426-4435 (fee applies)
United Kingdom
Animal PoisonLine: 01202 509000 (fee applies)
Australia
Animal Poisons Helpline: 1300 869 738
Varieties
A few rhubarb cultivars turn up in most gardens, and they are told apart mainly by the color of the stalk and how deep that color runs. These are the ones worth knowing on sight.
Victoria
Victoria is a vigorous heirloom whose green stalks blush pink at the base, and it is the cultivar most often raised from seed.
Canada Red
Canada Red carries its deep red color the full length of the stalk and eats sweeter and less stringy than most.
MacDonald
MacDonald bears tender, bright red stalks and resists root rot well, which makes it the pick for heavier soils.
Glaskins Perpetual
Glaskins Perpetual holds less oxalic acid and can be picked later into the season than other types.
How to propagate
The surest way to make more rhubarb is to split a congested crown into rooted pieces. Seed is a slower route, and the seedlings it throws are a mixed, unpredictable lot.
DivisionEasy
Early spring while the crown is dormant (fall is also possible) · 1-2 years before light harvest, with full harvest by the third year
Splitting a crown is the surest way to raise more rhubarb. Lift a dormant crown in early spring and cut it into pieces, each carrying one or two plump buds and a firm chunk of root, then replant with the buds set just at or below the soil line. Give each piece a year or two before a light pick, with a full harvest by the third year. Every division grows up true to its parent.
SeedModerate
Start indoors 8-10 weeks before the last spring frost, then transplant out · 2-3 years to a full harvest
Rhubarb grows from seed too, but slowly and with no promise of a match. Sow indoors 8 to 10 weeks before the last spring frost, set the seedlings out, and expect 2 to 3 years to a full harvest. The seedlings vary in color and vigor and will not come true to a named cultivar, so seed is for the curious while division holds a variety's looks.
Myths
The whole rhubarb plant is poisonous and none of it can be eaten.
Only the broad leaf blades are toxic, from oxalic acid and soluble calcium oxalates. The cooked stalks are a safe, everyday food that has gone into pies and crumbles for generations. Cut the blades from the stalks, throw them out, and eat the stalks.
Rhubarb stalks turn poisonous once the plant flowers or after a hot summer.
Flowering and heat leave the stalks unchanged. The toxin stays in the leaf blades, never the stalks, so a plant that has thrown up a flower head is still safe to pick. Cut off the flower stalk and the stalks keep coming.