Plants are extremely diverse organisms. And we should respect them for their ability to poison as well as feed us.
There is no set manner by which plants poison. Most must be eaten to become toxic, while others can be touched (in the case of skin reactions).
The toxicity depends on the amount of plant material ingested. For example, all parts of the sunflower (Helianthus annuus) fall on the "slightly toxic" plant list.
Since sunflowers are a large part of our snack food diet, this comes as a surprise. But it's a perfect example of toxicity as a function of ingested amount. Doesn't ice cream make us sick if we eat too much of it?
So, should we fear all plants in the landscape? Should we keep our children locked in boxes so they don't risk their lives around plants? Certainly not!
Just because a plant produces poisonous berries or leaves doesn't automatically exclude it from use in a home landscape.
In his book, Plants for Play, Robin C. Moore says the great majority of our landscape plants are "highly beneficial and perfectly safe" for children. But many plants contain poisonous substances and warrant precaution.
Adults should learn about their landscapes and be able to distinguish those plants that may be hazardous. In turn, they should caution their children about those plants and plant parts that carry toxins.
There is no need to make children afraid of plants. But there is a great need to change the child's perspective to that of respect for all plant life, so the child has less risk of exposure to dangers. The education process provides a great opportunity for parent and child to share and grow in enjoying the environment.
The age of the children playing in the yard is a major consideration when planning your landscape. Plants with berries at perfect heights for small children, such as the poisonous fall berries of Convallaria majalis (lily of the valley), are much more of concern for toddlers or small children than 10-year-olds.
Recent trends in home landscaping involve a strong wildlife interest as a major factor in plant selection. Homeowners are asking for plants that produce berries to feed birds, squirrels, chipmunks and other creatures.
These berries appeal not only to wildlife, but to small children as well. Patterning after parents picking blackberries, strawberries and other edible fruits may encourage a child to pick and eat other tempting, but poisonous, berries.
The best way to protect small children from plant poisoning is to teach them to not eat any plant parts without adult supervision until they are old enough to be positive that the plant is safe to eat.
We can't ignore plants -- the hand that feeds us, so to speak. Human and animal life can't exist apart from green flora. So we must learn how to live with it. This means plant education for all people, big and small.
Here are some common landscape plants and their toxic parts (from the book, Learning from Poisonous Plants).