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

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

A variety of common plant foods contain cyanide 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.

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 to MAFF in the UK because of its 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. Dig it up as the seeds can stay in the ground for a number of years. 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.

Iodine can be harmful
Iodine is a vital mineral for the body, but even small amounts of iodine can be harmful. Algae has become quite popular in some dog foods, even though it contains high amounts of iodine. The connection between iodine intake and thyroid disease is well documented and studied, not only in dogs but also in humans. Using your own discretion to supplement your hovawart's diet may cause more harm than good.