My portulacaria afra is getting tons of new leaves but they're all light green and fall off easily. This is nutrient deficiency if I've ever seen it, but fertiliser doesn't help. Any ideas? I don't think it's sunstress, either.
Ditto you're likely overwatering, which is making nutrients less available. Have you repotted it since you got it? If so, what kind of soil did you use? It needs soil with some organic matter but more perlite than typical potting soil so it drains well.
I'd pull it out of its pot and look at the roots. They should be whitish and firm, if they're brown and slimy they're rotten, and those need to be removed. I'd also stop watering for a long time. If it starts to get droopy or shriveled leaves you know it's thirsty again
I'd bet it's missing sunlight, those things thrive in direct sun.
Second guess is that it's overwatered... does that pot drain well the water? it should definitely not be sitting in water and I would not water it very often.
Thank you. It's definitely not too much shade, it has always been on a south facing window. Maybe the soil is garbage. I'll check the roots for rotting as soon as I have good new succulent soil.
I would recommend getting new soil and don't be afraid of having a high quantity of perlite/vermiculite and gravel. You want soil that doesn't retain much moisture, so avoid too high of a quantity of rich fertilizers, peat and clay. I also recommend getting it into the sunniest location you have in your house. If you're in the northern hemisphere, W and S are your best bet, West giving the most UV and hours of light per day.
The new growth may die back slightly from these conditions but it's okay: the new growth is weak and it's likely that trying to maintain the new growth in these conditions will only stress out the plant over time. I say it's better to just let the old die away and let the more resilient, hardy growth take over.