I’ve had this plant, in its original pot, for two years. It’s opposite a south facing window and gets filtered light. The plant has been sprouting new tall shoots and at the same time the shorter and older stems have their leaves turning yellow. I was advised to water thoroughly once a month. What should I be doing differently to stop the yellowing?
The ZZ plant (Zamioculcas zamiifolia) is often thought to be the perfect houseplant, because it is so easy to care for. However, it does need some attention. You can trim off any existing yellow or browning leaves and stalks now, then look for the cause.
We have provided detailed instructions to previous inquiries about growing the ZZ plant. This one is about general care and transplanting, which may be what your plant requires if it is still in its original pot. Within this response, you will find a link to an even more detailed response to another inquirer, about general care. When to transplant ZZ
At first glance, your photo doesn’t show evidence of crowding, but do check that there is room in the pot.
Bright, filtered light from a south-facing window is ideal, so I suspect that the yellowing is being caused by the watering practice.
Too much moisture is the primary cause of leaf yellowing in these plants. However, under watering can also cause leaves to yellow and develop brown tips!
As described in the responses, to which I have provided the link, watering thoroughly at 3-4 week intervals is probably fine, but it is important that the plant not sit in a saucer of water. When the top three inches of soil is dry to the touch (poke your finger into the soil) then it is safe to water again. But don’t let the soil dry out completely for any length of time.
Good luck with your ZZ plant!