Amy Stewart is the award-winning author of Wicked Plants, Wicked Bugs, and The Drunken Botanist, among other horticultural titles such as Flower Confidential, The Earth Moved and From the Ground Up. With a subtitle like “The Weed That Killed Lincoln’s Mother and Other Botanical Atrocities,” Wicked Plants is by far the most unique. Here is a little Halloween scare from the deadly, dangerous, destructive, illegal, and intoxicating plants you should take caution to prevent…

Deadly Blue-Green Algae: If Toxic Blue-Green Algae is not a convincing enough reason to curb overuse of synthetic fertilizer, I don’t know what is! Although scientists are still investigating what causes algae bloom, fertilizer runoff and warming water temperatures are two possible explanations. Blue-Green Algae are technically classified as bacteria. These tiny organisms can cause severe gastro-intestinal distress, seizures, paralysis, and even death. For more information about the threat of Blue-Green Algae, visit CDPH.

Dangerous Sago Palm: Use primarily as an ornamental, the Sago Palm has a stunning form, if not a very “soft” plant in the landscape. Not only is this plant estremely poky and sharp, it is highly toxic to animals, including huamns. According to ASPCA, the Sago Palm is one of the most harmful plants to pets due to the rapid effect a phytotoxin (cycasin) for which the plant is named (Cycas revoluta). 

Destructive Johnson Grass: Considered to be one of the ten worst weeds in the world, Sorghum halepense has adaptive characteristics that make it harmful to cattle and land alike. As a perennial weed, Johnson Grass crowds out cash crops in fields, vineyards, and orchards. It can produce toxic amounts of hydrocyanic acid, which is poisonous to livestock when eaten.

Illegal Opium Poppy: According to Stewart, this plant is the only Schedule II narcotic that can be ordered through a garden catalog or purchased at a nursery, despite a request from the DEA to stop domestic distribution.From the Middle East, papaver somniferum

has been cultivated for thousands of years. The plant itself is not illegal, but the seeds are due to the milky sap contained in the seed, which is used to produce opium, an ingredient in prescription pain medication. Poppy seeds are a popular food ingredient, but ingesting too much could result in a positive drug test! Read about famed food writer Michael Pollan’s encounter with this illegal plant.

Intoxicating Mandrake: Despite the curiosity incited by Harry Potter, this member of the Solanaceae family has a sordid history. The mangled roots resemble human figures, which may be why they are associated with superstitious practice, religion, and witchcraft. But if ingested, it can be hallucinogenic. Like all nightshades (e.g., tomatoes, peppers, potatoes, etc.) the plant roots and leaves contain alkaloids that cause unpleasant effects.

Of course, many of the above-listed are not first choices for school gardens, but the cautionary lessons from these types of plants have more general implications for school gardens:

1. Be weed wise. Take seasonal interest in the wickedest weeds in your school garden and keep records of how and when each weed is tamed. Follow Integrated Pest Management practices for the best results.
2. Know thy enemy. Just because a plant is poisonous, does not mean you can’t plant it. Be aware of what part of the plant is toxic (e.g., leaves but not fruit of tomatoes) and how much one would need to ingest to become ill.
3. Attempt to educate. Intentionally include some simple toxic plants, especially ones with visual interest (e.g., morning glory, foxglove, or larkspur). Just be sure to accurately label these plants and provide adequate warning signs.

The family name of these plants are not always dead giveaways, so be sure to do research before putting that oh-so-unique or coveted plant in the school garden. For more information about Wicked Plants, see Untamed Science.  Middle and High School teachers might enjoy this free CCSS aligned resource. Happy Halloween!