Why does my peace lily have yellow leaves?

My peace lily lived on top of a filing cabinet for two years, which tells you most of what you need to know about how much attention it got. It drooped, I watered it, it perked back up like a dog hearing the leash jingle, and I decided that was the whole relationship. Water it when it flops. Simple.

Then one week it flopped, I watered it, and it didn't come back the way it used to. Instead the bottom leaves — the oldest ones, closest to the soil — started going yellow at the base and working their way up. I did what anyone does: I watered it again, because yellow leaves look thirsty. A few days later two more leaves went. I remember standing there with the watering can, genuinely confused, thinking I was doing the responsible thing and getting punished for it.

That confusion is the whole story with peace lilies. They droop dramatically when thirsty, so people learn to treat drooping as a universal cry for water — and then they apply that lesson to yellowing too, which is a different signal entirely. Where the yellow shows up on the plant, and what the soil is actually doing underneath, tells you which of three completely different problems you've got.

The part where I made it worse

I want to be honest that my first move was wrong. I watered a plant that was already sitting in wet soil, because the leaves told me a story my hands should have overruled. Overwatered and underwatered plants look nearly identical from the outside — both cause drooping and yellowing — and the tell isn't the leaf, it's the soil. Bone dry means thirsty. Sopping wet for days means drowning. I hadn't checked the soil at all. I'd just watered on the schedule my brain had invented after two years of a plant that mostly ignored me.

What I eventually learned is that a fixed watering habit is close to the single biggest cause of both problems. The same plant might want water twice a week in a hot July and once every couple of weeks in January, because shorter days and cooler indoor temperatures cut water needs by something like 30 to 60 percent for most houseplants. My peace lily's filing-cabinet routine had worked by accident during summer and was actively drowning it by the time the yellow leaves showed up in fall.

Yellow leaves on peace lily: what the pattern actually means

Here's the breakdown, once I stopped guessing and started paying attention to where the yellow was and how the soil felt:

Yellow leaves at the bottom, soil still damp days after watering — this is classic overwatering, and specifically it's often the early signature of root rot. More houseplants die from root rot caused by chronically wet soil than from any pest, disease, or missed watering, and yellow lower leaves paired with soil that's still wet a week later is the textbook version of it. If you've also noticed little black flies hovering around the pot, that's not a separate problem — fungus gnats lay eggs in chronically damp topsoil, and they resolve on their own within a couple of weeks once the watering habit changes, no spray required.

Yellowing across the whole plant, older and newer leaves alike, soil bone dry — that's underwatering, plain and simple. A peace lily that's gone too long without water will yellow broadly rather than just at the base, and the soil will confirm it before the leaves finish confirming it for you.

Crispy, browning edges on otherwise green leaves — that's usually not a watering problem at all. It's tap water. Peace lilies are sensitive to the salts, chlorine, and fluoride in municipal tap water, and the edges take the damage first because that's where the plant deposits mineral buildup as water moves through the leaf. Letting tap water sit out overnight, or switching to distilled or rainwater, is the usual fix — it's a separate issue from over- or under-watering even though it shows up as discoloration too.

Most tropical houseplants, peace lilies included, want their soil moisture to drop into roughly the 20 to 40 percent range before you water again — the exact number shifts a bit by species, but the principle is the same across all of them: wait for the soil, not for the calendar.

What actually changed

I ended up buying a cheap four-in-one soil probe — the kind that reads moisture as a straight percentage, not a vague dial — mostly because I was tired of being wrong in both directions. The first reading I took, on the plant with the yellowing lower leaves, was still sitting around 65 percent nearly a week after I'd watered it. That's not a plant asking for water. That's a plant sitting in a swamp.

I started using Plant Tender after that, mostly because I didn't want to have to remember what "65 percent last Tuesday" meant relative to what it needs this Tuesday. You walk the probe around the house, point your phone camera at the reading, and the app tells you what that percentage means for that specific plant instead of you trying to hold every species' preferences in your head. It also tracks the trend over time, so if a pot that used to dry out in five days is suddenly still wet after ten, you see the shift before the leaves start dropping to tell you about it themselves. If you want to stop guessing the way I was guessing, plant-tender.com has the details, and signing up takes about as long as it took me to kill that one leaf.

The peace lily lost three leaves before I got it sorted, but the ones that came in after are still green, and the plant has stopped surprising me. It sits on the same filing cabinet. It just doesn't get watered because it drooped anymore.