Hi everyone,

I have noticed that a good amount of the leaves on my Pilea have started to discolor around the edges and in spots in the middle of the leaves, its not a browning or a yellowing, more like a translucent lighter green. I started noticing this a few months ago during the winter, none of the leaves affected have fallen off or died back. The parts of the plant that are affected are not soft to the touch at all. It also looks like the new growth on top is not being affected. As far as I can see, there are no visible signs of pests attacking my plant.

As for how I care for my plant:
I water about once a week, or when the top 2-3 inches of soil is dry
I fertilize with liquid fertilizer (following dilution directions on the bottle) during the spring and summer, so far I have only fertilized it once this year.
I keep my apartment between 64 to 74 degrees throughout the year (I am in zone 6b)
Unfortunately, I have a north-facing window so I have low light in my apartment, never getting direct sunlight.

So my current hypothesis is that it is discoloration from cold. I keep my plants in the brightest location in the apartment which is right next to the sliding door. And since my apartment is a bit outdated I feel like during the winter months (when I first started noticing this) the leaves were close enough to get some frostbite. Its also worth noting that my sister's Pilea is doing the same, it was a pup from this plant, she also keeps it near a window, but it is a better insulated one than mine.

I have searched high and low on the internet about this issue and I cannot find any definitive answer and I would love to hear anyones thoughts or ideas.

Thank you!

Oedema is a physiological disorder that develops when roots take up water faster than it can be used by the plant or transpired through the leaves. Water pressure builds up in the internal cells of the leaves causing them to burst, leaving dead cells that are visible as a blemish, primarily on the leaves. Add a couple of extra days between watering and it should be ok. Oedema may also be spelled edema.

I don't think its too bad, however I would only use fertilizer at 1/4 the manufacturer recommendations and only one time a year. The way I check to see when to fertilize is to test the run off with a TDS or a EC meter. If you have a lot of plants you may want to consider buying one. They are very helpful in Horticulture culture.

Many folks struggle with this plant. Yours appears to be doing better than most. Leaf discoloration on lower, older leaves is a common problem and is due at least in part to normal aging.

I suggest that you allow no more than the top inch of soil to get dry before you water it thoroughly.

The temperatures you cited are fine. North window light is also fine. The limited amount of fertilizer you have added is also not a problem.

Thanks for both of your help!

I'll check into Oedema more thoroughly, that could be it, maybe when I do water the plant I over water. So maybe I need to monitor how much water I'm giving it when I do. The weird thing it though, that with Oedema the damaged cells in the leaves typically start yellowing and turn brown as they die back, but I am not seeing this in my plant at all. These leaves have had this discoloration for months now with no further color change.

Another thought I had was that maybe it could be mineral deposits within the leaf? I live in a city and try to water my plant with either filtered water or the water from my dehumidifier, but more often than not this tactic doesn't fit in with my watering schedule. There are mineral deposits that the plant has excreted on the back of some of the leaves.

You are correct that the symptoms do not fit edema. Mineral deposits in water are also not likely to cause those symptoms, either.