Plants toxic to sheep include: Acorns
Angel trumpet (all parts)
Azalea (all parts)
Bittersweet (leaves, fruit)

Black Bryony
Bracken

Buckthorn (all parts)
Caladium (all parts)
Castor Bean (all parts)
Chinese Lantern (all parts)
Chrysanthemum (all parts)
Creeping Charlie (all parts)
Daffodil (bulb)
Delphinium (all parts)
English Ivy (all parts)
Foxglove (leaf, seeds)
Geranium (all parts)
Gladiola (bulb)

Hemlock (water dropwort)

Holly (all parts)
Horse Chestnut (flower, sprout, seeds)

Horsetails

Hyacinth (bulb)
Iris (all parts)
Jerusalem Cherry (leaf, unripe fruit)

Laburnum

Lily of the Valley (all parts)

Lupine

Mistletoe (all parts)

Monkshood

Mushrooms (all parts)
Narcissus (all parts)
Nightshade (all parts)
Oleander (all parts)
Peony (roots)
Philodendron
Potato (sprouts, vines, unripe tubers)

Ragwort

Rhododendron
Rhubarb (leaf, roots)

Green Hellebore
Stinking Hellebore
Sugarbeet tops (FRESH)

Trumpet Lily (all parts)
Vinca Vine (all parts)
Wandering Jew (leaf)
Yew (IMMEDIATELY toxic)
The above chart is from "Barnyard in Your Backyard" a book that we carry. Please see our books page for more information.
POISONOUS PLANTS
In raising livestock (or even pets and children) it's important to be aware of which plants (and which parts thereof) are poisonous. Many people inquire about buying sheep as "lawn mowers" or they put sheep (or other livestock) on unimproved land that may harbor one or more of these dangerous plants. If you intend to introduce animals to any area of your property, do a "nature walk" and be sure to identify what plants are growing there (including trees and shrubs) This is a partial list of plants compiled by Ag Agent Ken Bolton of Jefferson County, Wisconsin for FARMING. The plants in green are ones I have compiled from Dr. Henderson's book "The Veterinary Book for Sheep Farmers."
For a much more extensive list of poisonous plants, please visit Colorado State's webpage located here.
Pipestone's Toxicity Page
What to do if your sheep ingest a poisonous plant:
One veterinarian advised the following for sheep who had eaten rhododendrons - 4 tablespoons Milk of Magnesia (laxative plus antacid); 1 teaspoon baking powder; 1 teaspoon powdered ginger. Dosage was 2 ounces given twice, 12 hours apart. Also advised was to give them aspiring (3 per adult sheep)

IN AN EMERGENCY, administer charcoal from a firepit or fireplace to a poisoned sheep as soon as possible. There are charcoal products formulated on the market for poison cases, but if you don't have anything available. just scoop up some charcoat and break it up into small pieces and make the animal swallow it. I have a shepherdess friend who saved a ram from dying of cherry leaf poisoning by doing this.