The other way people wind up leaving with peace lilies is when they come up to me and say that they don't have a lot of light, but they want something that flowers, is there anything I can recommend? There aren't even any other good candidates: in that case it's pretty much peace lily or nothing. (Generally I try to talk people towards a nice non-flowering plant, if I can.)
So the flower shop guy and I commiserated for a while over our shared disgust for peace lilies.
Or, well, it wasn't exactly like that.
Certainly the word wouldn't be disgust. But all the same, peace lilies get way more attention than they deserve, and they're not easy enough that they should be everybody's first plant, though it increasingly seems like they are.
The pluses first. They do often have nice foliage. There is a medium-sized variety with thinner, glossy, very dark green leaves (wallisii?) that can be quite the knockout, whether in flower or not, and I am a huge fan of the very large cultivars ('Mauna Loa,' 'Sensation') because I find them significantly easier to care for than the medium and small ones. Plus being a sucker for large plants to begin with. There are also not many other indoor plants that can be induced to flower as easily or as abundantly, which is a plus if you like the blooms, though I find them hard to like, myself.
Breeders have also been working hard on getting new color variations of Spathiphyllum, which hasn't been exceptionally obliging, but there are a few: I have 'Golden Glow,' which is a bright chartreuse yellow2, and I have seen 'Domino,' a green-and-white variegated plant which is interesting if examined close-up. (The variegations on 'Domino' are often so fine that if you're not close enough to see them clearly, it just looks like the plant has gotten kind of dusty.)
And it's also a plus that the Spathiphyllum is willing to accept less light than most plants. That quality, though, is why they're so often labeled as easy-care plants, I think, and that's not quite right.
One of the more notable features of Spathiphyllum is that when it dries out, the leaves visibly droop, to the point where in severe drought, they will all lay flat on the ground. Give it water, and within a few hours, the leaves pop right back up to their original positions. This would be a good indicator of when to water, except that by the time things reach the point of laying flat, damage has been done: the roots die back slightly each time this happens, and if it happens often enough, it will eventually fail to come back at all. I suggest that beginners get to know your plants better than this: the drooping process lasts two or three days, from the first indication of dryness to leaves laying flat. If you know your plant well enough, you can see the change in posture on the first day, and water then, and never have to deal with a slumping plant.
Supposedly they flower better when rootbound, and supposedly flowering is mainly between April and September, though I would question both of these. My own plants have flowered better for me a few months after repotting, and – although this could be coincidental – also after being moved. (It seems not to matter where they've been moved to, or from, only that the location change. This has happened for me at least three times, with different plants.)
Spathiphyllum negatives: it's difficult to get the watering just right. If it's too dry, it'll let you know, by drooping, and that’s useful, though not something you want to rely on. If it's too wet, there's a tendency for plants to rot where they sit, except that they do it in such a way that you don't necessarily realize what's going on. One day you go to pull off a dead leaf, and a whole rootless plant comes out. This will generally not be salvageable. To make things trickier, the plant (like a lot of other plants) responds to being too wet by – you guessed it – drooping, which would make an inexperienced grower think that it needs more water.
A more subtle indicator of overwatering manifests as blackened leaf tips, which quickly spread to the margins of the leaf. The prevailing wisdom is that blackening leaf tips and margins means too much fertilizer or air that is too hot and dry, and it's true that a lot of plants do react this way. However, it's been my experience that, nine times out of ten, a peace lily with black leaf edges is suffering from root suffocation, either because its soil has broken down and compacted, or because part of the soil never gets to dry out. Especially in a very large pot, and especially especially in a plant that's been overpotted (put in a pot that's too large for the plant), and especially especially especially in a plant that's in a very large pot, too big for the plant, with no drainage hole, the top of the soil can dry out while everything after the top three inches is soaking wet. With very large plants, it's probably actually best to wait for the leaves to go a little limp before watering again.
Common sense is important. If your plant is droopy and the soil feels wet, the plant is obviously not drooping because it's too dry: don't give it water. If the plant looks fine and the soil feels dry, the plant doesn't need water just because the soil is dry: wait for the leaves to get a little limp first. Spathiphyllums are nothing if not good communicators.
They are also prone to go into sudden tailspins over nothing (or at least not over anything a new houseplant owner would be able to detect: the most likely cause is one of a few fungus infections that afflict Spathiphyllum more than most), which can make them frustrating. This isn't terribly common, but it's happened to me before, and I see it from time to time in the plants at work as well.
I do not find humidity to be an issue at all, ever. This will surprise some people, but, you know, show me a plant that's suffering because of dry air, instead of because it's too wet or too dry, and I'll change my mind. Until then, I wouldn't worry about it, because I've never seen a case where it obviously made a difference.
In the time I've been at Garden Web (since Dec. 2006), I've seen more people post about issues with their peace lilies than any other plant, no contest: too many marketers think that the only important thing about a plant is how much light it needs. It's true that Spathiphyllum doesn't require a lot of light; that doesn't make it the best plant for you, any more than knowing Jennifer Anniston's name makes her your best friend.
photo credit: a Garden Webber who prefers to remain nameless
1(This happens with distressing frequency. Maybe as much as 90% of the people who don't really care what they get and just want to buy something wind up with one or the other of these. Jade plants, Crassula ovata, make up the bulk of the remaining ten percent.)
2(When I saw the 'Golden Glow' for the first time, I started grinning uncontrollably and couldn't stop myself. I think it was also on sale, too, which made the grinning problem worse. My husband, who was with me at the time, was mildly confused by this, but he's seen stranger interactions between me and plants, so it didn't faze him hugely or anything. 'Golden Glow' has turned out to be a relatively unproblematic cultivar, though I'm still not entirely used to the color, eight months later.)