Vegetable · Polygonaceae
Rhubarb
Rheum rhabarbarum
Plant it once and rhubarb pays you back for years, with tart red stalks every spring and big leaves you simply leave alone.
Full sun
Every 5–10 days
365–730 days
USDA 3–8
Overview
Rhubarb is the rare vegetable that earns its keep in the dessert bowl. The tart red and green stalks cook down into pies, crumbles, and jam, which is how it picked up the old name pie plant. It belongs to the knotweed family and shrugs off cold that would kill most garden crops, surviving winters down to -40°F (-40°C).
What sets rhubarb apart is patience. Plant a crown once and it settles in as a long-lived perennial, sending up fresh stalks every spring for a decade or more before it needs dividing. You skip the harvest the first year and take only a little the second, but from the third year on it gives back generously.
One thing to keep straight from the start: you eat the stalks, never the leaves. The big leaf blades hold oxalic acid and are toxic to people and animals, so they get cut off and thrown out. Master that one rule and rhubarb is about as easy as gardening gets.
Care
The short version: full sun, deep and fertile soil, and steady moisture with about an inch of water a week. Feed in early spring as the crown wakes, mulch to keep it cool, and lift and divide the crown every several years to keep the stalks coming strong.
Light
Rhubarb wants full sun for the best stalks, though it puts up with partial shade in warmer regions. The more light it gets, the thicker and more productive the crop comes in.
Water
Keep the soil evenly moist but never waterlogged, which works out to about an inch (2.5 cm) of water a week. Water more deeply through hot, dry spells, and lay down a thick organic mulch to hold moisture and keep the crown cool.
Soil
Plant in deep, fertile, well-drained loam worked full of organic matter. A pH between 6.0 and 6.8 suits it, and good drainage is the one thing rhubarb won't forgive, since a soggy crown rots.
Temperature
Rhubarb is built for cold and takes temperatures from -40°F to 86°F (-40°C to 30°C). It actually needs a real winter chill to go dormant and come back strong, and it sulks where summers stay hot.
Humidity
Average outdoor humidity in the 40% to 60% range is plenty, so there's no number to fuss over. Air moving freely through the big leaves matters more, since crowded, damp foliage invites leaf spot.
Feeding
Feed once in early spring as the crown breaks dormancy, using a balanced fertilizer or well-composted manure. Rhubarb is a hungry feeder, so rich soil and that yearly spring boost keep the stalks thick.
Pruning
Cut out the central flower stalk at its base the moment it appears, or the plant pours its energy into seed instead of stalks. Pull off any dead, yellowing, or frost-damaged leaves, and always bin the toxic blades rather than feed them to animals.
Repotting
Rhubarb stays in the ground, but the crown needs dividing every 5 to 10 years to stay vigorous. Thin, spindly stalks or a clump dying out in the center are your cue to lift it, split it, and replant the strong pieces.
Size & spacing
A mature plant reaches 2 to 4 feet (60 to 120 cm) tall and spreads just as wide, so give each crown 3 to 4 feet (90 to 120 cm) of room. Those big leaves need space for air to move and for the plant to fill out.
When to plant
Rhubarb runs on the cold. Set out dormant crowns in early spring as soon as you can work the soil, then hold off harvesting that first year while the plant builds its roots. Stalks come in spring through early summer, with 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 tough, and most of its troubles trace back to a crowded crown, soggy soil, or summer heat. Learn to read the stalks and the leaves and you can catch a problem early. Match what you see below, then act before it sets the plant back.
A soft, brown crown and a collapsing plant
This is crown rot, usually from wet feet in soil that drains too slowly, sometimes driven by a soil fungus like Phytophthora. There's no saving a rotted crown, so dig it out and destroy it. Replant healthy divisions on a raised, well-drained site, and never pile mulch right against the crown.
Fix:
- Remove and destroy affected crowns
- Improve drainage and replant healthy divisions on a raised, well-drained site
A tall flower stalk shooting up from the center
This is bolting, the plant's push to set seed when summer turns hot or the crown gets old and crowded. It drains energy the stalks need, so cut the flower stalk off at its base the moment you spot it. Keep the plant watered and mulched, and divide tired old crowns to head it off next year.
Fix:
- Cut the flower stalk off at its base as soon as it is seen
- Keep plants consistently watered and mulched
Stalks coming up thin, short, and weak
Thin stalks almost always mean an overcrowded crown that has outgrown its space, though poor soil and over-harvesting add to it. Lift and divide the crown in early spring, replant the strongest pieces, and feed with compost or a nitrogen-rich fertilizer. Ease off the harvest for a season so the plant can rebuild.
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
Spots or chewed holes on the big leaf blades
Round tan-to-purple spots point to a fungal leaf spot such as Ascochyta or Ramularia, while ragged holes are the work of slugs or the rhubarb curculio. Pull off the worst leaves and destroy them, open the planting up for better airflow, and water at the base. Hand-pick the beetles and stay on top of 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 safe and dangerous parts, so the line matters. The cooked stalks are good food, but the large leaf blades hold oxalic acid and anthraquinone glycosides that are toxic to people, cats, dogs, horses, and livestock. Cut the leaves off, throw them out where no animal can reach them, and never feed trimmings to pets or grazing stock.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds
Safe for
People
Cats Moderate
A cat that nibbles the leaf blades usually starts drooling and pawing at its mouth, then vomits and turns sluggish. A large mouthful is worse, since the oxalates can bring on tremors and strain the kidneys.
Dogs Moderate
Expect drooling, an upset stomach, a lost appetite, and a dog that just wants to lie around after it chews the foliage. Eat enough and the same crystals can trigger tremors and kidney damage.
Horses Moderate
The blades irritate a horse's mouth and set off heavy drooling, colic-like cramping, and weakness. A big feed risks lasting kidney harm, so fence them away from the foliage.
Rabbits Toxic
The oxalic acid in the leaves is genuinely dangerous to rabbits and there's no safe amount. Keep the blades and trimmings out of reach entirely.
Livestock Toxic
Cattle, sheep, and goats that graze the leaves can suffer severe oxalate poisoning, with drooling, gut pain, staggering, and kidney failure. Never toss leaf trimmings into a pasture or pen.
Birds Toxic
The same oxalic acid and anthraquinone compounds make the leaves unsafe for poultry and pet birds alike. Don't let backyard hens scratch through discarded blades.
People Stalks safe
Cooked rhubarb stalks are a kitchen classic and safe to eat, but the leaf blades are not. They hold oxalic acid that brings on a burning mouth, nausea, and vomiting, so trim the leaves off and throw them out.
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
Only a handful of rhubarb cultivars turn up in most gardens, and they differ mainly in color, sweetness, and how well they hold up. These are the ones worth knowing by name.
Victoria
A vigorous heirloom with green stalks blushed pink at the base, and the one cultivar most often grown from seed.
Canada Red
Keeps its deep red color all the way up the stalk and runs sweeter and less stringy than most.
MacDonald
Carries tender, bright red stalks and good resistance to root rot, which makes it the pick for heavier soils.
Glaskins Perpetual
Its lower oxalic acid content stretches the harvest later into the season than other types allow.
How to propagate
Rhubarb is easiest to multiply by splitting an established crown, though you can also start it from seed if you don't mind the wait and a little surprise.
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
Division is the surest way to make more rhubarb. Lift a dormant crown in early spring and cut it into pieces, each with one or two strong buds and a good chunk of root, then replant with the buds sitting just at or below the soil line. Give it a year or two before a light pick, and a full harvest comes by the third year. Best of all, every division stays 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
You can grow rhubarb from seed, but it's slow and a bit of a gamble. Sow indoors 8 to 10 weeks before your last spring frost, then transplant out, and expect 2 to 3 years before a full harvest. Seedlings vary and won't come true to a named cultivar, so save seed for the adventurous and stick with division for known varieties.
Myths
The whole rhubarb plant is poisonous and none of it can be eaten.
Only the leaf blades are toxic, thanks to oxalic acid and soluble calcium oxalates. The cooked stalks are a safe, everyday food that has filled pies and crumbles for generations. Cut the blades off, bin them, and enjoy the stalks.
Rhubarb stalks turn poisonous once the plant flowers or after a hot summer.
Flowering and heat don't make the stalks toxic at all. The poison lives in the leaf blades, never the stalks, so a bolting plant is still safe to harvest. Just snap off the flower stalk to keep the crop coming.