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"Poisonous" does not mean deadly. Some manifestations of toxicity are subtle. The dose, as always, determines if a plant is safe source of nutrients or a toxic hazard.

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BRIEF: Do you have any information on the pyrus, prunus and malus genus of trees?

Our landscape firm is working on a garden design for elderly persons, including some with Alzheimer's/dementia. As you may or may not know, late stage Alzheimer's patients often eat whatever plant material they come across, and it is therefore important that we not include highly toxic plants in our plant list. However, many plants that are listed as toxic are not necessarily toxic to humans, or need to be consumed in such large quantities in order to be toxic, that poisoning is very unlikely to occur. We would like your opinion on the overall toxicity levels of the pyrus, malus and prunus genus of trees. I have consulted the Canadian Agricultural Department's database of poisonous plants online, and a couple of other sources which say they contain cyanide, including the seeds, leaves and stems. If this is so, do you have any idea how much of these parts of the plant would have to be ingested before they would likely causetoxic poisoning? The answer to this question would greatly aid us in our decision as to whether or not to use the plants.


Pear and apple trees are not particularly toxic, nor are the ripe fruit. The seeds contain amygdalin, which is a glycoside that can release cyanide. One would have to eat a lot of seeds to ever get cyanide poisoning by this route. If eating the seeds were incidental to eating the apples, I think you would OD on apple before getting sick from cyanide. Same with pears. Cherries and other members of the prunus genus have more amygdalin in the leaves than apples and pears, but I don't think they would eat enough fresh leaves to do them in before they were caught at it. Freezing or wilting increase the rate of cyanide release, but I think you would need to make a tea or something to get in trouble. On the other hand, eating the nut inside the peach or apricot pit (other members of prunus) as if it were an almond can be harmful, especially in quantity. The landscaping that can kill include oleanders, yew, and to some extent, privet. many herbaceaous ornamentals (foxeglove, castor, etc.) can cause a problem, too. It does not take much of these plants to cause serious illness or death.