Saturday, April 18, 2009

Houseplant Toxicity Week: Part 1 (Introduction and Disclaimers)

If you have landed on this page because you are concerned about a child or pet who has eaten a plant, seek emergency medical help.

In the U.S., you can call Poison Control at 1-800-222-1222 (for children), the ASPCA at 1-888-426-4435 (for pets; $60 consultation fee applies), or the Pet Poison Helpline at 1-800-213-6680 (pets; $35 fee applies)
Part 1 of a seven-part-and-two-appendix series. (Part 2) (Part 3) (Part 4) (Part 5) (Part 6) (Part 7) (Appendix 1) (Appendix 2 - Index)

And it begins.

As I explained a couple weeks ago, this was originally planned to be a single, albeit very long, post, and then when I realized that it was on-track to be roughly the size of a smallish novel, I had to scrap that plan and come up with a different way of presenting the information. So I have divided the houseplant-toxicity list into seven posts (plus two appendices), which will go up over the course of this week. I'm not entirely happy about dividing it up, but nobody's going to read a 19000 24000 word post all in one sitting.

Lantana camara 'Rose Glow Improved.' Like all Lantana, it is toxic.

So this post is for the introduction and disclaimers. Let's do the disclaimers first:

1) I cannot guarantee that the information which follows is accurate, though I have done the best I could, and I'm fairly certain about most of it. When possible, I have referred to books which are specifically about plant toxicity and have beaucoup scientific references to back up what's being said. For other plants, I've used on-line lists (when a consensus existed) or used guilt-by-association (assuming that plants in the same family, and especially in the same genus, share similar levels of toxicity).
2) Differing species will react differently to the same plant. What is toxic to parrots will not necessarily be toxic to turtles, or cats, or babies. For the most part, my references are interested in humans, not pets, so my list is also primarily focused on humans. Some humane societies, pet enthusiast websites, etc., have their own lists, all of which I find problematic in some way or another (or else I wouldn't have felt compelled to come up with my own), but if you're interested in safety for a specific organism, you should probably also consult a list particular to that organism, however questionable some of the information in it might be.1 When a normally-safe plant is known to be exceptionally harmful to a particular species of interest, I have tried to note this in the text.
3) Even a normally safe species has the potential to be harmful if it has recently been treated with a pesticide, particularly systemic pesticides (which are by design taken up into the tissues of the plant). I did not find evidence that this kind of poisoning has ever actually happened, at least not in humans: the amounts involved would not normally be enough to matter.2 But it's not impossible.

Agave victoriae-reginae, I think. Since writing that profile, I've become less certain about the ID. Agave spp. are, of course, potentially dangerous due to their spines, even if they weren't also somewhat toxic and indigestible.

4) Plants that are not actually poisonous may still be dangerous if ingested due to spines, thorns, etc. and should still not be eaten. (It does sometimes happen that a thorn or sharp projection can slice or perforate esophagus or intestines or whatever on the way through the system of an animal or child. It's rare, and in any case you should already know that there are thorns or whatever and consider the plant dangerous enough to keep out of reach -- you knew about people poking their eyes out, if not about the intestine thing -- but even so I figure I should say it explicitly.) I have taken this into account when deciding which list to place certain thorny plants in.
5) Plants which are not actually poisonous may, on rare occasion, cause potentially life-threatening allergic reactions in susceptible individuals. Allergic reactions are hard to predict, vary in intensity, may develop over time, can happen in response to pretty much any plant, and happen more often with plants that are dangerous for other reasons anyway, so I haven't made a point of taking this into account.

Ficus benjamina 'Midnight.' Ficus spp. cause allergic reactions in a lot of people, though these are rarely if ever life-threatening. I personally mostly just get itchy.

6) In the interests of not making the post any longer than it absolutely had to be, I've declined to provide photos of all of the plants. I've included a few pictures throughout the posts, for decorative / illustrative purposes, and if the plant was the subject of a PATSP profile, I linked to the profile, where there will be other pictures. Googling a plant name will normally turn up a picture anyway, so do that if there's a question.
7) I have chosen very deliberately to include a lot of information here, because I feel like I'm having to serve a lot of masters at once (dog owners, parents, herp enthusiasts, recreational drug users, recreational drug users with snakes and children but not dogs, etc.) and I figure it's better to include stuff that may not be relevant to you than it would be to leave something out that is. So this is not going to be a quick and clear reference to everything you want to know. There will be extraneous information. I would have given you only the information you wanted to know if I knew in advance what information that was.
8) I make frequent reference to two books:
Nelson, Lewis S., Richard D. Shih, and Michael J. Balick. Handbook of Poisonous and Injurious Plants, 2nd ed., Springer Science + Business Media, New York, NY, 2007.
Spoerke, David G., Jr., and Susan Smolinske. Toxicity of Houseplants, CRC Press, Inc., Boca Raton, FL, 1990.
These are often abbreviated to Handbook and Toxicity, respectively, in the text. Just in case you wanted to know where this is all coming from.

Epipremnum aureum. One of a gazillion plants that contain microscopic needles of calcium oxalate, so that if you try to bite them, they stab you back, causing pain and swelling and so forth. Dangerous-ish, insofar as it hurts a lot but usually nobody dies.

9) Please do try to keep this all in perspective. Most of the time, ingestion of a houseplant is not going to result in serious problems. Dangerous plants absolutely do exist, but it's actually very rare that anyone dies, or even has any serious long-term effects. According to one site, in the U.S. in the year 2000, there were six deaths due to "other and unspecified venomous animal or plant" (i.e., either the animal wasn't identified, it was an animal other than snake, lizard, spider, hornet, wasp, or bee, or it was a plant), which even if all six were plants, I'd be surprised if all six were houseplants. By contrast, hornets/wasps/bees killed 82 people in that year, and suicide killed 32,637. So not only are you probably safer indoor gardening than outdoor gardening, you're (statistically) at least a few hundred times safer alone in a room with your houseplant than you are alone in a room with yourself.3 4 5

So anyway. I'm very much in favor of people knowing which plants they have and how dangerous they are. I approve of people taking some basic precautions to keep plants out of the reach of kids and pets. I think there are situations where you should wear goggles (and maybe long sleeves) if you're pruning or taking cuttings to propagate. I think keeping kids and pets away from plants, and making sure they're not top-heavy (the plants, not the kids and pets6) and won't tip over on the kids, is a good thing. I also think there are situations where it's handy to know what's what, just so you can make an educated choice and buy safer plant B instead of the more dangerous plant A. However. I do not approve of some of the sites I came across in the course of the research here, which seemed to be less about useful information than trying to scare people: I don't think ZOMG YR PLANTZ WILL KILL U W/ POIZEN!!!1!!!!1!!!! is a realistic or useful message, even though some of them sure enough can.

If readers have direct personal experience about any plant, whether on or off of this list (or if anyone outside the U.S. wants to let me know about their country's version of Poison Control and how to contact them, for the advice at the top of the post), please leave it in the comments. I probably will not have the time to respond individually to each and every comment, but that doesn't mean that your feedback might not prove to be useful to someone else, and eventually I will get around to checking out whatever it is, so please, don't hold back.

Tradescantia zebrina. Mild skin irritant for a few people. Generally considered safe.

So here's how the rest of this is going to work. I've divided plants into six categories, according to level of danger. The first five are:
Crazy super dangerous, Dangerous, Potentially dangerous, Unpleasant, and Safe. The sixth category, Unknown/could not determine, is for plants where I either found no information or conflicting information. If anybody knows for certain one way or the other on those, or if anyone disagrees strongly with the placement of a plant on the following lists, please speak up in the comments and I will adjust the post accordingly (if I think you've made your case suitably well: I'm not going to change the post every ten seconds just on some random person's say-so, however wonderful that random person might be. Scientific references, if available, carry a lot more weight with me than anything else. Just so you know.).

Tomorrow it begins. We'll start with the ninjas ("crazy super dangerous").


Photo credits: all are my own.

1 Because it was requested, I have tried to flag specific plants I'm reasonably certain are safe for terrariums including reptiles or amphibians. Pretty much anything that doesn't have sharp points (Agave, e.g.), corrosive sap (Euphorbia), or highly toxic sap (Adenium) should be okay for carnivores: for example, most of the species in the Araceae, though they are toxic if eaten, are safe for animals that aren't going to try to eat them and aren't big enough to crush them.
2 If, for example, you put pesticide granules totaling 500 mg of pesticide in the soil of a plant, 500 mg is the absolute maximum possible dose, and that's only if the whole thing -- pot, drainage water, plant and all -- is eaten. In reality, this is very unlikely, and most of the pesticide will be in the soil at any given time. That still might be enough to be dangerous, of course, but if you've followed the label directions (Which you should always do), it's very unlikely that harmful amounts will be ingested from the plant itself. Ingestion of the straight pesticide, right out of the bottle, is a lot more likely. It's silly to sit around wringing your hands about your maybe-toxic houseplants if you leave your bug sprays, cleaning products, antifreeze, rat poisons, etc. unsecured.
3 Toxicity of Houseplants says that in 1987, there were 88,251 reported cases of plant exposure for which medical attention was sought, only thirty-one of which were "serious," and only one of which resulted in a fatality. And the one fatality was from a garden plant, not a houseplant. So this appears to be somewhat consistent from year to year. And by the way: hooray for Interlibrary Loan! And a big thank-you to the University of Wyoming (Laramie) Library!
4 Obviously pets are a different story, and pet-related statistics are much less complete, and pets are probably more likely to have serious consequences from eating a houseplant.
5 The math is kind of tongue-in-cheek here: obviously the risk from ingesting a plant is mostly a function of how likely you are to ingest it, and it may be that there aren't many houseplant poisonings because there aren't more houseplants, or aren't more babies, or because most people can't keep houseplants alive long enough for them to pose a risk, or whatever. But even so, it's uncommon, and for the majority of the plants I looked up, even in the cases where someone actually did eat a plant that was actually poisonous, they didn't eat enough of the plant to have any symptoms, or the symptoms were there but relatively limited.
Another, if ickier to contemplate, way to look at all this would be to say that in a hypothetical U.S. where everybody's future cause of death was printed on their forehead, for every one person you saw whose forehead said "other and unspecified poisonous animal or plant," you'd meet or see 5400 people whose foreheads read "suicide," and 118,000 "heart attacks." In fact, about half of all the people you met, saw on television, or saw pictures of in ads and photos would say "heart attack," "cancer," or "stroke," just those three. So in the long run, you should be about 118,000 times more worried about heart disease killing your kid than about your houseplants killing your kid.
6 Though there's probably a post to be written about the dangers of top-heavy pets, too. Children not so much, because I think it's general knowledge that they tend to tip over.


our friend Ben said...

Go Mr. S.! Maybe somebody will publish your series as a book/pamphlet so it gets wider distribution. Maybe the BBC? You should check into it in your abundant spare time...

our friend Ben said...

Oops, that's BBC as in Brooklyn Botanic Garden, not British Broadcasting Company...

Anonymous said...

Great post. I'm looking forward to the rest of the series. I've already learned some interesting things! Thank you.

Unknown said...

I'll be a faithful reader, as always: this is an important subject, and one I have written about in the real world as it pertains to dogs, cats, horses, and probably very soon, cattle. (for outdoor plants, that is!) I'm glad you're doing this series, but you could write about lint and i'd be here cheering you on.

Anonymous said...

Great idea, great start - looking forward to the rest. Second the thought of getting it published somewhere - also the comment that I'd read the blog even if you were writing about lint!

CelticRose said...

This looks like it's really going to be good. I like how you're including allergic reactions -- I have sensitive skin and now I know not to buy a Ficus.

I agree with the comments saying you should get this published. An easy-to-read, accurate guide on houseplant toxicity is definitely needed. Perhaps you could even expand it into a book?

John de said...

Really excited to see more!

mr_subjunctive said...


Well it's funny you should say that, because I do have some thoughts on lint. The Margaret Atwood novel Cat's Eye contains a reference to an artist who washed towels in large quantities to generate lint, and then cut the sheets of lint and glued them to some kind of backings to make "lintscapes." Which I always thought sounded like a really awesome idea, and have wanted to do myself, but lack of a personal washer/dryer and an inadequate towel supply have kept me from attempting it.

I think Atwood says in a preface that there's a real artist who is/was doing those. I should try to find out who.

our friend Ben / Anonymous / CelticRose:

Well, I don't know if this is going to be particularly easy to read, actually. Though it does have jokes, which I'm guessing is rare (if not unprecedented) in plant-toxicity lists. So it would have that going for it.

I'm wondering what all is going to be in Amy Stewart's new book, Wicked Plants (which I have pre-ordered from Amazon, thank you very much): the descriptions I've seen so far make it sound like it's going to be sort of a natural history of multiple (outdoor?) toxic plants, kind of doing for poisonous plants what Michael Pollan's The Botany of Desire did for apples, tulips, marijuana, and potatoes. Though I'm not sure how detailed she's going to get. In any event, maybe Stewart beat me to it, which I think would make her even more my nemesis than she already is.

thepoisongarden said...

Hooray for starting out by saying that the actual amount of harm directly caused by plants is small.

Most garden writers who write about poison plants don't seem to get this and tend to cry wolf. A lot.

I've got one book which asserts that holly should not be brought into the house because the berries are poisonous which completely ignores the fact that holly has been brought into millions of homes at Christmas for many, many years and, if I recall correctly, there has been one case of a child vomiting after eating the berries.

Taste is the important factor. Most poison plants, believe me, taste awful and that's what stops you eating a harmful amount.

I look forward to the rest of the series. My knowledge is, primarily, about garden plants which grow in northern Europe but, I'm sure, there will be some overlap.

Kenneth Moore said...

Hm, it took me a second to understand that "herp enthusiasts" didn't refer to people who enjoy the herp, but to people who like cute little lizards like Nina.

Can't wait for the posts this week!

I wonder if many Solanaceae will be on the list... I know potato leaves etc. can be poisonous, even though potato leaf tea was used as an aphrodesiac a few hundred years ago. Oh funny olde-thyme people!

I should look into toxicity of common garden vegetables. Maybe when it's harvest time. :-D

Anonymous said...

Thanks for spreading the word on plants that are poisonous to our pets on your blog - so important for pet owners to be aware of the lurking household poisons in (and outside of) their house! As an ER specialist, I see so many toxicities that owners bring in too late (making it more expensive to treat, with a worse prognosis!). When in doubt, it's so important to call a Poison Control for peace of mind!

I wanted to make you aware of another important resource out there also - Pet Poison Helpline is an additional Animal Poison Control Center, and it's one of the most cost-effective animal poison ($35/case vs. ASPCA's new $60/case) controls out there nowadays. Unfortunately, because animal poison controls are not federal- or state-funded, there is a fee to allow the service to be run 24-7. We provide a similar service, but have the added benefit of veterinary specialists (in internal medicine and emergency and critical care) as part of our staff. You can always call 1-800-213-6680 if you ever have a problem. Thanks for spreading the word!

Dr. Justine Lee, DVM, DACVECC
Associate Director of Veterinary Services