Are Oxalis plants poisonous? - Plant Care Guide

Yes, Oxalis plants (commonly known as wood sorrel or shamrock plants) are toxic due due to their high content of oxalic acid and soluble oxalates. While a small, incidental taste by humans or pets might only cause mild irritation due to the tart flavor, ingesting larger quantities can lead to more severe symptoms, including digestive upset, kidney damage, and tremors, particularly in pets.

What is Oxalic Acid and Why is it Harmful?

Oxalic acid is a naturally occurring organic compound found in many plants, including Oxalis species, spinach, rhubarb, beet greens, and cocoa. While present in varying concentrations, in high amounts, it can be harmful due to its interaction with calcium in the body.

Here's a breakdown of what oxalic acid is and why it's harmful:

• Chemical Structure: Oxalic acid (HOOC-COOH) is a dicarboxylic acid, a relatively strong organic acid.
• Mechanism of Harm (Binding to Calcium):
  1. Calcium Sequestration: The primary mechanism of harm is that oxalic acid readily binds with calcium (and other minerals like magnesium and iron) to form insoluble crystals called calcium oxalates.
  2. Nutrient Depletion: When ingested in large quantities, oxalic acid can bind with the body's free calcium, effectively removing it from the bloodstream. This can lead to a calcium deficiency (hypocalcemia), which can disrupt normal bodily functions, including nerve impulse transmission, muscle contraction, and blood clotting.
  3. Irritation and Damage to Tissues: The insoluble calcium oxalate crystals can precipitate in various tissues, causing irritation and damage:
     • Mouth and Throat: Immediate irritation, burning sensation, swelling, and numbness due to contact with the crystals.
     • Digestive Tract: Can cause gastrointestinal upset, vomiting, diarrhea, and abdominal pain.
     • Kidneys: If absorbed into the bloodstream, calcium oxalate crystals are filtered by the kidneys. In high concentrations, they can accumulate in the renal tubules, forming sharp crystals that can cause kidney damage, kidney failure, and urinary tract issues.
• Toxicity Level: The toxicity of oxalic acid depends on:
  • Concentration in the plant: Some plants (like rhubarb leaves) have very high, dangerous concentrations. Others (like spinach) have lower, manageable concentrations.
  • Amount Ingested: Small amounts are generally harmless or only cause mild irritation. Large quantities are problematic.
  • Body Weight: Smaller individuals or pets are more susceptible to the effects of a given amount.
• Symptoms of Oxalic Acid Poisoning:
  • Immediate: Burning sensation in mouth/throat, swelling, drooling, vomiting, diarrhea.
  • Delayed/Severe (high doses): Lethargy, weakness, muscle tremors, difficulty breathing, changes in urination, collapse, and kidney failure.

While Oxalis plants do contain oxalic acid, the amount required to cause severe toxicity is generally high. However, its presence makes all parts of the plant considered potentially harmful, especially if consumed in quantity.

What Symptoms Do Oxalis Plants Cause in Humans?

Ingesting Oxalis plants can cause several symptoms in humans due to the presence of oxalic acid and soluble oxalates. While accidental nibbling is unlikely to be life-threatening, it can be quite unpleasant.

Here are the typical symptoms Oxalis plants can cause in humans:

• Immediate Mouth and Throat Irritation:
  • Burning Sensation: The most common immediate symptom is a noticeable burning or stinging sensation in the mouth, tongue, and throat. This is due to the sharp calcium oxalate crystals coming into contact with mucous membranes.
  • Numbness: A feeling of numbness, especially around the mouth or on the tongue, can also occur.
  • Swelling: Mild swelling of the lips, tongue, or throat is possible.
  • Drooling: Increased salivation (drooling) may be observed as the body tries to flush out the irritants.
• Gastrointestinal Upset (if larger amounts ingested):
  • Abdominal Pain: Stomach cramps or discomfort.
  • Nausea and Vomiting: The body's natural response to ingesting an irritant or toxin.
  • Diarrhea: Can occur, especially if significant quantities are consumed.
• Bitter or Tart Taste:
  • Oxalis leaves have a distinctive sour or tart taste (like lemon or sorrel) due to the oxalic acid. This taste often acts as a natural deterrent, preventing people (and animals) from eating large quantities.
• Rare, Severe Symptoms:
  • While extremely rare from typical ornamental Oxalis species (which usually aren't consumed in large enough volumes), very large ingestions could theoretically lead to systemic effects such as tremors, weakness, and kidney issues, similar to severe rhubarb leaf poisoning. However, this is highly unlikely from casual exposure to houseplant or garden Oxalis.

Important Note: If any amount of Oxalis has been ingested by a human, especially a child, it is always best to contact a poison control center for advice. They can assess the risk based on the amount ingested and the individual's symptoms.

What Symptoms Do Oxalis Plants Cause in Pets?

Oxalis plants can cause more severe symptoms in pets than in humans due to their smaller body size and sometimes a greater tendency to consume larger quantities. The oxalic acid and soluble oxalates can lead to a range of issues, particularly affecting the gastrointestinal system and kidneys.

Here are the typical symptoms Oxalis plants can cause in pets (dogs, cats, and even livestock):

1. Immediate Mouth and Throat Irritation:
   • Drooling/Hypersalivation: This is often the first and most noticeable sign in pets. The oxalic acid irritates the mouth and causes excessive drooling.
   • Paw at Mouth: Pets may paw at their mouth or appear to be trying to clear something from their throat due to irritation.
   • Vocalization: Whining or crying due to discomfort.
   • Facial Swelling: Less common, but can occur.
2. Gastrointestinal Upset:
   • Vomiting: A very common symptom as the body tries to expel the ingested plant material.
   • Diarrhea: Can be present.
   • Abdominal Pain: Evidenced by restlessness, hunching, or reluctance to be touched in the abdominal area.
   • Loss of Appetite: The pet may refuse food due to discomfort.
3. Systemic Effects (with larger ingestions):
   • Tremors and Shaking: Due to the impact on calcium levels, which affects nerve and muscle function.
   • Weakness and Lethargy: The pet may appear unusually tired, weak, or uncoordinated.
   • Kidney Damage/Failure: This is the most serious concern, especially with large ingestions. The calcium oxalate crystals can form in the kidneys, leading to:
     • Changes in urination (increased or decreased urination).
     • Kidney pain.
     • In severe cases, acute kidney failure, which can be fatal.
   • Changes in Blood Calcium: Hypocalcemia (low blood calcium) can lead to more profound neurological and cardiac issues.
4. Distinctive Odor in Vomit (sometimes):
   • Some pet owners report a sour or bitter smell in the pet's vomit due to the oxalic acid.

Important Note: If you suspect your pet has ingested any amount of Oxalis, it is crucial to contact your veterinarian or an animal poison control center immediately. They can provide guidance on whether to induce vomiting, monitor for symptoms, or seek emergency veterinary care, depending on the amount ingested and the pet's size. Early intervention can be critical in preventing severe kidney complications.

Which Types of Oxalis are Common in Gardens and Homes?

There are numerous species within the Oxalis genus, and several types are commonly found in gardens and homes, both as cultivated ornamentals and as persistent weeds. All of these contain oxalic acid.

Here are the common types of Oxalis:

1. Ornamental Oxalis (Cultivated for Beauty):
   • Description: These are grown specifically for their attractive foliage (often purple, green, or variegated) and delicate, trumpet-shaped flowers (pink, white, or yellow). They are often sold as houseplants or bedding plants.
   • Characteristics: Typically grow from small bulbs or rhizomes. Their leaves often fold up at night or when stressed.
   • Examples:
     • Oxalis triangularis (Purple Shamrock or False Shamrock): Very popular houseplant with deep purple, triangular leaves that resemble butterflies and delicate pinkish-white flowers.
     • Oxalis regnellii (Green Shamrock): Similar to O. triangularis but with green leaves.
     • Oxalis tetraphylla (Iron Cross Oxalis): Four-lobed leaves with a distinctive dark purple blotch in the center. Pink flowers.
     • Varieties of Oxalis versicolor (Candy Cane Sorrel): Grown for its striped, candy-cane-like flower buds.
2. Weedy Oxalis (Common Garden Pests):
   • Description: These are often persistent and invasive weeds in lawns, garden beds, and cracks in pavement. They are prolific seed producers and can spread rapidly.
   • Characteristics: Typically have small, clover-like (trifoliate) leaves and small yellow or pink flowers. They often have explosive seed pods that can fling seeds several feet when touched or dry.
   • Examples:
     • Oxalis corniculata (Creeping Wood Sorrel, Yellow Wood Sorrel): The most common garden weed. Has small, green or reddish-purple clover-like leaves and tiny yellow flowers. Spreads aggressively by runners and explosive seed pods.
     • Oxalis stricta (Upright Yellow Wood Sorrel): Similar to O. corniculata but grows more upright.
     • Oxalis pes-caprae (Bermuda Buttercup): A highly invasive bulbous Oxalis in warmer climates (e.g., California). Forms large clumps of clover-like leaves and bright yellow flowers.

Table: Common Oxalis Types

Regardless of whether they are ornamental or weedy, all these Oxalis species contain oxalic acid and should be managed with caution around children and pets.

What is the Difference Between Soluble and Insoluble Oxalates?

Understanding the difference between soluble and insoluble oxalates is important for comprehending the varying toxicity of plants containing oxalic acid. Both forms can be harmful, but they manifest their effects differently.

• Oxalic Acid (Free Acid): This is the soluble form.
• Calcium Oxalate Crystals (Insoluble): This is the insoluble form, which is a salt of oxalic acid.

Here's the distinction:

1. Insoluble Oxalates (Calcium Oxalate Crystals):
   • Form: These are sharp, needle-like crystals of calcium oxalate (raphides) that are physically present within the plant's cells. These crystals are insoluble in water and relatively stable.
   • Immediate Effect: When chewed or ingested, these sharp, microscopic crystals directly penetrate and irritate the mucous membranes of the mouth, throat, and gastrointestinal tract.
   • Symptoms: This causes immediate symptoms like:
     • Intense burning or stinging sensation.
     • Numbness or tingling.
     • Swelling of the lips, tongue, or throat.
     • Excessive drooling.
     • Gastrointestinal upset (vomiting, diarrhea).
   • Plants with High Insoluble Oxalates: Many common houseplants, including Peace Lilies (Spathiphyllum), Dieffenbachia, Philodendrons, Pothos, and Caladiums, are high in insoluble oxalates. These plants cause immediate, intense irritation but are rarely fatal because the immediate pain prevents large amounts from being ingested.
   • Action: The primary concern is localized irritation and potential airway swelling if a large amount is ingested, but systemic toxicity (kidney damage) is less likely from insoluble oxalates alone.
2. Soluble Oxalates (Oxalic Acid and its Soluble Salts):
   • Form: These are free oxalic acid molecules or soluble salts of oxalic acid (e.g., sodium oxalate, potassium oxalate) that are dissolved within the plant's sap.
   • Systemic Effect: When ingested, these soluble oxalates are absorbed into the bloodstream from the digestive tract. Once in the bloodstream, they bind with free calcium (and other minerals).
   • Symptoms: This can lead to:
     • Hypocalcemia: Low blood calcium, affecting nerve and muscle function (leading to tremors, weakness, irregular heartbeats).
     • Kidney Damage: The calcium oxalate crystals precipitate in the kidneys, forming sharp stones that can block renal tubules, leading to kidney dysfunction or failure.
     • Gastrointestinal upset (vomiting, diarrhea) can also occur.
   • Plants with High Soluble Oxalates: Plants like Oxalis species, rhubarb leaves (stems are safe), spinach (in very high quantities), and beet greens contain significant amounts of soluble oxalates. These plants pose a greater risk of systemic toxicity if consumed in large quantities.
   • Action: The primary concern is systemic poisoning, particularly kidney damage.

Why Oxalis is Problematic:

Oxalis plants are unique because they contain both soluble oxalic acid and insoluble calcium oxalate crystals. This means they can cause both immediate mouth/throat irritation and pose a risk of systemic toxicity (kidney damage) if sufficient quantities are ingested. This dual action makes them a significant concern, especially for pets.

What to Do if Oxalis is Ingested by Humans or Pets?

If Oxalis is ingested by humans or pets, immediate and calm action is crucial. While a small taste might only cause mild irritation, it's always best to err on the side of caution and seek professional advice to assess the risk.

For Human Ingestion:

1. Do NOT Induce Vomiting: Unless specifically instructed by a medical professional, do not try to make the person vomit. This can cause further irritation or complicate the situation.
2. Rinse Mouth: Encourage the person (especially a child) to thoroughly rinse their mouth with water.
3. Offer Water/Milk: Give small sips of water or milk to help dilute the oxalic acid and soothe the throat. Milk can help bind some of the soluble oxalates.
4. Contact Poison Control: Immediately call your local Poison Control Center. In the USA, this is 1-800-222-1222.
   • Be prepared to provide:
     • The exact name of the plant (if known, e.g., Purple Shamrock, Creeping Wood Sorrel).
     • The part of the plant ingested (leaves, stems, flowers).
     • The approximate amount ingested.
     • The age and weight of the person.
     • Any symptoms observed.
   • They are experts and will provide precise instructions based on the situation.
5. Seek Medical Attention (If Advised or Severe Symptoms): If the person develops severe symptoms (difficulty breathing, extensive swelling, persistent vomiting/diarrhea, tremors) or if advised by Poison Control, go to an emergency room or seek immediate medical care.

For Pet Ingestion:

1. Do NOT Induce Vomiting: Unless specifically instructed by a veterinarian or animal poison control, do not try to make your pet vomit.
2. Remove Remaining Plant Material: Carefully remove any remaining plant material from the pet's mouth.
3. Rinse Mouth (Cautiously): If safe to do so, gently rinse your pet's mouth with water.
4. Contact a Veterinarian or Animal Poison Control: Immediately call your veterinarian or an animal poison control center.
   • ASPCA Animal Poison Control Center: 1-888-426-4435 (consultation fee may apply).
   • Pet Poison Helpline: 1-855-764-7661 (consultation fee may apply).
   • Be prepared to provide:
     • The exact name of the plant (if known).
     • The part of the plant ingested.
     • The approximate amount ingested.
     • Your pet's species, breed, age, and weight.
     • Any symptoms observed (drooling, vomiting, tremors).
   • They will guide you on whether to monitor at home, seek emergency vet care, or bring the pet in for examination.
5. Bring a Sample (If Possible): If you visit the vet, bring a sample of the ingested plant for identification.

Prevention is always best: If you have Oxalis (ornamental or weed) in areas accessible to curious children or pets, consider removing it or placing it out of reach.

How Do I Safely Remove Oxalis Weeds from My Garden?

Safely removing Oxalis weeds from your garden is a persistent challenge due to their aggressive growth, prolific seed production, and sometimes bulbous nature. While their toxicity to humans and pets is a concern with large ingestion, the primary motivation for removal is their invasive weed status.

Here's how to safely remove Oxalis weeds:

1. Manual Weeding (Most Effective for Small Infestations):
   • Method: This is the best method for control. Dig out the entire plant, ensuring you get the full taproot or the entire underground bulb/rhizome system.
   • Timing: Best done when the soil is moist (after rain or watering) as it's easier to pull the roots intact.
   • Crucial for Bulbous Varieties: For species like Bermuda Buttercup (Oxalis pes-caprae), ensure you remove all tiny bulblets. Leaving even one behind means it will regrow.
   • Dispose Safely: Place all removed Oxalis plants in a sealed plastic bag and dispose of them in the trash. Do NOT compost them, as seeds and bulblets can survive composting and re-infest your garden.
2. Prevent Seed Production:
   • Method: Regularly prune or snip off flower stalks before they go to seed.
   • Why: Many Oxalis species (like Creeping Wood Sorrel) have explosive seed pods that can fling seeds several feet, spreading rapidly. Preventing seeds is crucial for long-term control. Use sharp garden snips.
3. Mulching:
   • Method: After clearing an area of Oxalis, apply a thick layer of organic mulch (3-4 inches) like wood chips, straw, or shredded leaves.
   • Benefit: Blocks sunlight from reaching the soil, preventing new Oxalis seeds from germinating. It also smothers small existing plants.
4. Solarization (for Large, Infested Areas):
   • Method: For heavily infested bare garden beds, cover the area with clear plastic sheeting during the hottest months of summer. Secure the edges. The sun's heat builds up underneath, "cooking" and sterilizing the top layers of soil, killing seeds and bulblets.
   • Benefit: Can significantly reduce large populations of Oxalis.
   • Consideration: Takes several weeks to months.
5. Vinegar (Household Herbicide - Use with Caution):
   • Method: A spray of concentrated horticultural vinegar (10-20% acetic acid, not household vinegar at 5%) can effectively kill Oxalis foliage on contact.
   • Caution: This is a non-selective herbicide, meaning it will kill any plant it touches, including desirable ones. It also does not kill the roots or bulbs, so repeat applications are necessary. Always wear protective gear (gloves, eye protection). You can buy horticultural vinegar.
6. Herbicides (Chemical - Last Resort):
   • Method: For very severe and widespread infestations, a broadleaf herbicide might be considered.
   • Caution: Always use extreme caution. Choose products specifically labeled for Oxalis and safe for your garden type. Follow all label instructions precisely. Avoid use around edibles or areas frequented by pets/children.

Long-term strategy: Oxalis often indicates compacted or disturbed soil. Improving overall soil health with organic matter and consistent mulching will make your garden less hospitable to this persistent weed over time. Persistence is key when dealing with Oxalis.