Readers may be surprised to learn that some of their favorite plants have toxic components. As designers, we need to be aware of plant toxicity for the gardens and landscapes we create. For example, if designing a children's garden or a dog park, specifying oleanders would be ill advised because of their toxicity. We do, however, need to understand what is meant by the terms toxic or poisonous plants.
New Zealand's Science Learning Hub offers a comparative, where toxins are specific compounds that make something poisonous. If we look at our oleander example, oleandrin is a toxic compound formally known as a cardiotoxic glycoside, a sugar that when ingested can cause illness or death depending upon the individual circumstance. This is a key point, understanding a plant's toxin will help understand the potential harm to humans, animals, and even insects. When researching plants, references will note poisonous plants, but it will be up to the designer to evaluate levels of potential harm for specific sites. Again, we can look at oleanders, a species we see all over California, in public spaces, along our freeways, and in home gardens, where designers and homeowners have determined that the danger is low. The same evaluations can be made for most plants, but it is up to the designer or anyone purchasing plants to be informed.
This section is not evaluative. The purpose here is to note plants that contain toxic compounds; the reader should pursue further research to understand if specific plants are right for their gardens or landscapes. There are some places to start, for example, North Carolina State University Extension provides considerable information on poisonous plants, such as our example, Nerium oleander. However, I caution wholesale dismissal of plants just because they are identified as poisonous. Once again, let's look at oleanders, a desirable plant within rural communities where deer are prevalent. This is purely anecdotal, but I have known people in Sonoma County observing deer eating oleanders, then coming around the garden for more. We know two things from this observation; 1) deer were eating oleander because it was late in the summer season when their normal food can be scarce, and 2) they survived whatever stomachache they might have experienced to come back again. This example is only intended to encourage reader to do their homework to understand the level of danger by specific plants, and consider the site, the users of the site, and any potential risk.
For people and pets, the dangers can vary, from minor skin or eye irritation to nausea, heart palpitations, or death. Simultaneously, we may be surprised by just how many poisonous plants are around us everyday without causing injury. They provide other benefits that should also be considered for landscape designs.
With that said, consider this garden dedicated to the deadliest plants in the world.