© Dieter Weber (User:Uellue) · CC BY-SA 3.0 · Commons
Rhubarb
Caution🐾Rhabarber · (Rheum rhabarbarum)
Knotweed family (Polygonaceae)
Description
Only the leaf stalk of garden rhubarb (Polygonaceae) is edible — traditionally harvested from April until St John's Day in late June, after which oxalic acid content rises too sharply. Its sourness comes from oxalic acid (0.5–1.5% in the stalk) and malic acid; cooking removes some acid, but rhubarb should still be eaten in moderation by anyone with kidney stones or gout. The root contains the same anthraquinone glycosides (sennosides, emodin, rhein) recognised as a medicinal drug in Chinese rhubarb, though at lower, more variable concentrations; at low doses it stimulates digestion, at higher doses it acts as a laxative — not for more than one to two weeks without medical supervision. Crucially, the leaves are toxic from their very high oxalic acid content and must never be eaten — they can cause vomiting, kidney damage and, rarely, fatal poisoning.
CONTRAINDICATED during pregnancy
Rhubarb root preparations are contraindicated in pregnancy: anthraquinones (emodin, sennosides) are embryotoxic in animal experiments and may stimulate uterine contractions. Rhubarb stalk as food in usual culinary amounts is considered safe, but should also be restricted due to oxalic acid.
CONTRAINDICATED during breastfeeding
Anthraquinones from rhubarb root pass into breast milk and may cause laxative effects in the infant. Rhubarb root preparations are contraindicated during lactation. Rhubarb stalk as food in small amounts is acceptable.
Critical drug interactions with:
Herzglykoside (Digitalis, Digoxin)
The petiole (stalk) of garden rhubarb is the only edible part of the plant and is used in cooking as a vegetable and compote fruit. It contains oxalic acid (approx. 0.5–1.5 %) and malic acid, which give it its sour taste. Cooking partially destroys oxalic acid; nevertheless rhubarb should not be eaten daily in large quantities. Leaves and root are unsuitable for culinary use (see warning).
Preparation & dosage
The Kommission E has issued a positive monograph for Rhei radix (rhubarb root): at low doses (0.1–0.3 g crude drug) as a bitter and stomachic for digestive weakness, at higher doses (1–4 g) as a stimulant laxative for constipation. The main active constituents are anthraquinone glycosides (sennosides, rhein-8-glucoside, emodin glycosides). Important note: the Kommission E monograph refers primarily to R. palmatum and R. officinale (medicinal rhubarb from China); garden rhubarb (R. rhabarbarum) contains the same class of active compounds in the root but at lower and more variable concentrations — it is not pharmacopoeially standardised as Rhei radix.
Preparation & dosage
Pour 200 ml of boiling water over 0.5–2 g dried, ground rhubarb root (R. rhabarbarum), steep for 10 minutes, strain. One cup in the evening. Do not use for more than 1–2 weeks without medical supervision. Note: Standardised Rhei radix preparations use R. palmatum/officinale.
- Dry amount
- 0.5–2 g
- Doses per day
- 1×
- Max duration
- 2 weeks
In folk medicine and older phytotherapy, rhubarb root tincture was used as a bitter tonic to stimulate bile flow and gastric juice secretion (dyspepsia, bloating). The bitters (emodin, rhein) stimulate liver secretion and intestinal motility. In small amounts (bitter dose) the tonic effect predominates; in larger amounts the laxative effect takes over.
Preparation & dosage
20–30 drops of 1:5 tincture (40–60 % ethanol) before meals in a little water. No longer than 2 weeks without a break.
- Doses per day
- 3×
In folk medicine, decoctions of rhubarb root were applied as compresses for skin itching, minor inflammations, and wounds. The tannin content (tannins, galloylglucose) acts astringently; emodin shows antibacterial activity in vitro. This external use is transmitted only through folk healing tradition.
Preparation & dosage
Simmer 5–10 g dried rhubarb root in 300 ml water for 15 minutes, allow to cool, then strain. Apply compress to affected skin areas.
- Dry amount
- 5–10 g
- Doses per day
- 2×
WARNING — TOXIC: Rhubarb leaves contain very high amounts of oxalic acid (up to 1 % oxalate as soluble potassium oxalate + insoluble calcium oxalate) as well as anthraquinones. Ingestion of rhubarb leaves can cause severe poisoning: vomiting, kidney damage, convulsions — in rare cases fatal. Leaves must NOT be eaten. Historically, rhubarb leaves were used externally (as a 'green soap') for removing stains — now obsolete.
Preparation & dosage
Rhubarb leaves are TOXIC (high oxalic acid and anthraquinone concentration) — never eat. The stalk (vegetable) is safe when cooked, but should be avoided or restricted in kidney stone disease (calcium oxalate stones), renal insufficiency, or arthritis due to oxalic acid. Rhubarb root (anthraquinone laxative): do not use for more than 1–2 weeks without medical supervision. Chronic use of anthraquinone laxatives leads to electrolyte losses (potassium depletion), pseudomelanosis coli, and laxative dependency. Rhubarb root anthraquinones are suspected genotoxic and carcinogenic with long-term use (EFSA/BfR assessment of emodin 2018/2021). ASPCA classification (accessed 2026-08-10): toxic to dogs.
⏱ Max continuous use: 2 weeks
Rhubarb root preparations are contraindicated in pregnancy: anthraquinones (emodin, sennosides) are embryotoxic in animal experiments and may stimulate uterine contractions. Rhubarb stalk as food in usual culinary amounts is considered safe, but should also be restricted due to oxalic acid.
Anthraquinones from rhubarb root pass into breast milk and may cause laxative effects in the infant. Rhubarb root preparations are contraindicated during lactation. Rhubarb stalk as food in small amounts is acceptable.
Rhubarb stalk (vegetable, cooked) suitable for children from approx. 2 years in small amounts. Rhubarb root as a laxative not recommended for children under 12 years (insufficient safety data, electrolyte risk). Leaves strictly contraindicated.
Drug interactions
Herzglykoside (Digitalis, Digoxin)
Chronic use of anthraquinone laxatives can lead to potassium depletion. Hypokalaemia considerably increases the toxicity of cardiac glycosides.
Antiarrhythmika (Klasse I und III, z.B. Amiodaron, Chinidin)
Hypokalaemia from laxative misuse potentiates the arrhythmogenic effect of antiarrhythmic drugs.
Antikoagulantien (Warfarin, Phenprocoumon)
Emodin and rhein inhibit CYP enzymes in vitro; possible influence on anticoagulant metabolism with long-term rhubarb root intake.
Contraindications
- Intestinal obstruction (ileus) — contraindication for all anthraquinone laxatives
- Renal insufficiency and kidney stone disease (calcium oxalate stones) — due to oxalic acid in the stalk and anthraquinones in the root
- Chronic inflammatory bowel disease (Crohn's disease, ulcerative colitis)
- Pregnancy and lactation (rhubarb root preparations)
- Known hypersensitivity to rhubarb or anthraquinones
Harvested part: leaf stalks (April–June, traditionally until 24 June / St. John's Day)
- Time of day:
- Harvest in the morning, break or cut stalks close to the base. Do not eat the leaves.
- Drying:
- Do not dry stalks — use as fresh vegetable or process into compote, jam, or juice. For stalk juice: press fresh.
- Storage:
- 1 months — Fresh stalks: cool (4–6 °C), wrapped; up to 1 week. Frozen: up to 12 months (blanched).
- Time of day:
- Autumn (October–November) or spring (March) before budding — anthraquinone content is highest. No time-of-day restriction.
- Drying:
- Clean root, slice, and dry at 40–50 °C. Store dried material in well-sealed, dark containers.
- Storage:
- 24 months — Dark, dry, cool (below 20 °C), airtight — protects light-sensitive anthraquinones.
- Sennoside A und B (Dianthron-Glykoside)GlycosideContent: 0,5–3 %Root
Principal compounds for the Kommission E indication; stimulate intestinal motility via propulsion and inhibit fluid reabsorption in the colon. Standardised in Rhei radix as total hydroxyanthracene derivatives.
- Emodin (Trihydroxymethylanthrachinon)GlycosideRoot
Free anthraquinone aglycone; laxative, antibacterial in vitro; suspected genotoxic with chronic high-dose exposure (EFSA 2018). Sensitive to light and heat.
- Rhein (Cassiglucoside)GlycosideRoot
Monohydroxy anthraquinone glycoside; cholagogue and mildly anti-inflammatory in vitro; main intestinal metabolite alongside emodin.
- Oxalsäure (Oxalat)OtherContent: 0,5–1,5 % im Stiel; bis 10 % im BlattLeaf
In the stalk: potassium oxalate (soluble, absorbable, nephrotoxic in high amounts). In the leaf: highly concentrated — acute poisoning risk. Cooking the stalk partially inactivates oxalic acid.
- Tannine (Gallotannine, Ellagtannine)TanninRoot
Astringent tannins in the root; explain the folk medicinal external use as a wound remedy; partly antidiarrhoeal effect at low doses.
- Stilbene (Resveratrol-Analoga, Rhapontigenin)Phenolic acidRoot
Stilbenoids typical for Rheum roots; antioxidant, weak oestrogen-like activity; rhapontigenin as a marker for garden rhubarb root vs. R. palmatum.
- CatechinFlavonoidAerial parts
Flavan-3-ol in the stalk and leaf; antioxidant; contributes to the overall polyphenol profile.
- Äpfelsäure (Malat)OtherContent: 1–2 % im StielAerial parts
Organic acid in the stalk; alongside oxalic acid mainly responsible for the sour taste; physiologically harmless.
- [1]MonographKommission E Monographie: Rhei radix (Rhabarberwurzel) — Bundesanzeiger Nr. 22a, 1.2.1990(accessed: 2026-05-24)
- [2]MonographEFSA Panel on Food Additives (2018): Safety of emodin as a feed additive — EFSA Journal 16(1):5131(accessed: 2026-05-24)
- [6]MonographASPCA Animal Poison Control — Pie Plant (Rheum rhabarbarium)(accessed: 2026-08-10)
- [7]MonographCliniTox Giftpflanzen — Rheum rhabarbarum L.: schwach giftig (+) (Institut für Veterinärpharmakologie und -toxikologie, Universität Zürich)(accessed: 2026-08-10)
- [5]BookPlants For A Future (PFAF): Rheum rhabarbarum — Rhubarb(accessed: 2026-05-24)
- [3]WikipediaWikipedia DE: Rhabarber (Rheum rhabarbarum)(accessed: 2026-05-24)
- [4]WikipediaWikipedia EN: Rhubarb (Rheum rhabarbarum)(accessed: 2026-05-24)
🤝 Permaculture Partners
In your garden, this plant acts as:
✨ Best symbiotic partners
- 🌿 Garlic Garlic deters rhubarb pests and root fungi.
- 🌿 Cabbage Rhubarb leaves shade the soil, cabbage benefits from the retained moisture.
- 🌿 Red cabbage Rhubarb leaves shade the soil — red cabbage likes it too.
- 🌿 Lettuce Lettuce as ground cover beneath the large rhubarb leaves.
⚠️ Better not planted together
- 🥬 Carrot Both deep-rooting — compete for the same root space.
📦 Part of these planting sets:
Source: Helga und Margarete Langerhorst, Mein gesunder Naturgarten (eigene Kuration)