A Dozen Potentially Harmful or Toxic Herbs to Avoid in Chicken Keeping

Most herbs have wonderful health benefits for both humans and animals and have been used down through the ages to treat, prevent and cure all kinds of ailments, but not all herbs are safe. As you likely know, I do use lots of herbs with my chickens, both in their environment and diet, but I am careful to stick to the common, culinary herbs which are safe and perfectly edible, because some herbs are toxic to chickens (and humans as well!).
While nearly anything can be harmful in exceedingly large dosages, even plain drinking water, several herbs, beneficial as they may be at the correct dose, can cause illness or even death in fairly small amounts. And since little to no scientific study has been done as far as a safe dose for chickens, and I'm not a vet or medical professional, I just choose to err on the side of caution and stay away from anything that could be a potential problem. Just because something is labeled 'herbal' or 'natural' doesn't mean it's safe. And since chickens are so small, it doesn't take much to cause serious health problems.

Some of the following potentially harmful herbs appear in all kinds of poultry products sold commercially or in homemade concoctions sold or recommended by individuals, so you want to always check the ingredient list before using any kind of herbal supplement or product with your flock - just to be on the safe side. Even if the chicken aren't meant to eat a particular product, I avoid any product that contains any ingredients that could be potentially harmful, since as we know, chickens like to nibble and taste even things not necessarily meant to be eaten! Here's a list of some of the potentially toxic herbs I try to stay away from. At the least, they can cause some pretty serious symptoms in your flock at high doses; at worst, most can cause death.

A Dozen Potentially Harmful Herbs

Aloe Vera
Abdominal pain and diarrhea can be the result of ingesting aloe vera, so while it's great topically on burns and skin injuries, its best not to use it with your chickens, who are likely to peck at anything you administer to them. Bitter Orange
If your chickens get a hold of some bitter orange, that could result in loss of consciousness, stroke or a heart attack or death.
Comfrey Taken internally in large enough amounts, comfrey can cause diarrhea or liver failure as well as cancer of the liver. Better used as an external poultice to reduce swelling or inflammation and help to heal wounds, comfrey tea is widely enjoyed by humans and many long-time chicken keepers swear by comfrey as chicken fodder. So just use caution and your own judgement with this one.

Comfrey photo credit: Bake Creek Heirloom Seeds

Eucalyptus
White not toxic itself, Eucalyptus leaves can harbor Aspergillosis spores (a dangerous fungus that can cause death in various types of birds, including chickens and ducks).
Also full-strength eucalyptus oil is toxic to both humans and animals. If you plan on using eucalyptus around your flock, be sure you are getting it from a reputable source to reduce the risk of Aspergillosis.
Foxglove (digitalis)
Foxglove, also known as digitalis, can cause heart failure in animals and humans.

Foxglove in our front flower garden - pretty, but deadly

Henbane
It's no surprise that an herb called "henbane" would be potentially risky to use around chickens! It can cause heart problems, coma and even death.

Henbane photo credit: Princeton.edu

Horse Nettle Horse nettle, which is in the nightshade family, affects the central nervous system.
Monkshood/Wolfsbane
Monkshood (also called wolfsbane) can cause heart palpitations, respiratory distress, abdominal pain, nausea, vomiting or even death if ingested.

Monkshood photo credit: Poison.org

Pennyroyal
Although a member of the mint family, which is generally innocuous and perfectly safe to ingest, pennyroyal is toxic, resulting in liver failure and eventual death.

Pennyroyal photo credit: Wikipedia

Tansy Tansy should be avoided around chickens. It can cause diarrhea, liver disease, blindness, the inability to swallow and even death.

Tansy photo credit: Illinois Wildflowers

Tea tree/Melaleuca
Tea tree is one of the more popular essential oils for everything from an anti-inflammatory, antifungal and antibacterial to exczema and healing wounds, but if taken internally and cause vomiting, paralysis, seizures, unconsciousness and even coma.
Wormwood/Artemesia/mugwort
While wormwood is an old-timers method of battling parasites, wormwood affects the nervous system and can cause abdominal pain and convulsions which can lead to seizures if ingested in large amounts. Best to steer clear.

Wormwood photo credit: Seedsavers.org

Note: Be Very Cautious Using Essential Oils

Essential oils are extremely concentrated and powerful and can be very easily misused or given in too large amounts unless you have specific training in using them or are using precise dosages, so I always opt for fresh or dried herbs instead of using oils.
For a list of the safe, beneficial culinary herbs that I use in my chicken keeping and their various health benefits for your chickens, read HERE.

Even though nesting herbs, which I love sprinkling around my coop for my girls, aren't meant to be eaten, I still only use completely safe and edible herbs in my mixes. Rose petals, lavender, calendula, chamomile, and peppermint are a few of the ingredients I specifically like to use.

References/further reading: http://www2.hawaii.edu/~amybrown/PotentiallyHarmfulHerbList%20-%20Table.pdf https://www.ars.usda.gov/pacific-west-area/logan-ut/poisonous-plant-research/docs/tansy-ragwort-senecio-jacobaea/ http://www.webmd.com/vitamins-supplements/ingredientmono-729-wormwood.aspx?activeingredientid=729 https://www.beautyofbirds.com/safewoods.html http://healthyeating.sfgate.com/can-eucalyptus-oil-dangerous-8476.html https://www.allotment-garden.org/comfrey/feeding-comfrey-poultry-livestock/ http://www2.hawaii.edu/~amybrown/PotentiallyHarmfulHerbList%20-%20Table.pdf