Although there are many plants that are toxic or poisonous to dogs relatively few are fatal.

List of toxic/poisonous plants to dogs

Dog owners should never assume that human food is safe for their pet.

At least 1,000 species of plants and micro-organisms from 90 families have been shown to contain one or more of nearly twenty compounds capable of producing cyanide (Seigler, 1976) including garden beans and peas, and members of the rose family, especially bitter almond, peach and apricot, along with cherry, loquat, and apple. The flesh of these fruits (the part we eat) does not contain the cyanide, but the seeds do. Tapioca (Cassava root) must be specially processed (by drying and washing) to remove the cyanide prior to consumption. Contact with water removes the cyanide from the food and releases it into the air.

Some plants contain cyanide amongst other things in their leaves, which discourages herbivores and insects from eating them - but if eaten, digestion converts it to cyanide gas, which can quickly lead to asphyxiation by disrupting the conversion of oxygen into energy within cells. In addition to plants some insects can produce cyanide. Species of centipedes, millipedes, beetles, moths and butterflies synthesise and excrete cyanide for defensive purposes

In nature many neurotoxins are found in plant and animal matter; for example the neurotoxin aesculin is found in the horse chestnut (Aesculus hippocastanum) and the California Buckeye or California Horse-chestnut (Aesculus californica).

Examples of very dangerous or toxic plants

The castor bean or castor plant (Ricinus communis) contains Ricin and can be fatal causing hemorrhages of the heart, degradation of the kidneys and liver and intense inflammation and erosion of intestinal membranes.

Ragwort - Senecio jacobaea, and Ben Weed are notifiable in the UK because of their toxicity to livestock. If you have it on your land, dig it up and burn it. Do not leave it lying around as its toxicity increases and the roots can regenerate and the seeds can stay in the ground for a number of years. All three species of Senecio contain Pyrrrolizidine alkaloids. Dogs and other animals may die by eating a small amount whilst grazing on long grass.
List of toxic/poisonous plants to dogs

Cocoa bean mulch is poisonous to dogs.

The mulch, a byproduct of chocolate production is sold as garden mulch. The smell of the mulch is attractive to dogs, and they sometimes eat it. The mulch contains a chemical called theobromine, which is poisonous to dogs. The mulch causes a gastrointestinal upset when dogs eat it in small amounts. Large qauntities can cause gastrointestinal obstruction, tachycardia, muscle tremors and seizures.

If your dog eats this mulch, immediately contact your veterinarian.

Raisins & Grapes are toxic

Grapes of all varieties and growing conditions (including homegrown) have been implicated. Raisins are usually made from white seedless grapes, but all raisins of any source should be considered kidney toxic (chocolate covered raisins as well).

The toxic principle is unknown. Grapes contain low amounts of tannins compared to acorns, a known kidney toxicant in large animals. Grapes lack significant amounts of Vitamin D, another known kidney toxicant. It is unlikely pesticide residue is involved due to the wide variety of grape types involved. So far the majority of toxicosis reports have been in dogs. However, feeding grapes or raisins to cats and ferrets should also be discouraged, as poisonings have been reported in these species as well. Raisins, having lost their water content are considered more toxic

The symptoms?

Symptoms appear 6-24 hours after the dog eats raisins or grapes (average is 12 hours). Initially, symptoms are gastro-intestinal signs, followed by kidney problems. Vomiting is usually the first sign, with diarrhea, depression/lethargy, anorexia, colic, dehydration and sharply decreased urine output.

If your dog eats grapes or raisins, immediately contact your veterinarian.

Poisoned wildlife

The use of poisoned bait is cruel, indiscriminate and a special threat to dogs. The secondary fatal poisoning of domestic pets and wildlife is well documented; often via contaminated carcasses, killing dogs, cats, birds of prey, as well as foxes and badgers.

Strychnine for example has been banned in most countries for many years, but other equally potent substances are still in use and are illegally used to intentionally poison wildlife.

Including the following :- Alpha chloralose Carbofuran – a very toxic carbamate pesticide sold under the trade names Furadan and Curater, amongst several others. Fluoroacetate - (Sodium monofluroacetate ) highly toxic to mammals and insects. (a dose of 2–10mg/kg of fluoroacetate is lethal to humans).

Winter hazards

Many dogs are attracted to the sweet taste of anti-freeze, screen wash and some types of de-icers. They contain ethylene glycol which is an extremely dangerous chemical that is poisonous to dogs even in small amounts. Local authorities and others use chemicals and salt to melt the ice on roads and pavements, it can irritate their pads and be toxic if swallowed. Rinse it off the paws when you get home or try some special "snow boots" designed for dogs.