ZZ plant lower leaves yellowing — I was watering wrong the whole time
I've had a ZZ plant in my living room for two years. It was fine — until it wasn't. Lower leaves started turning yellow, one by one. I lost 6 leaves over three months before I figured out why.
I was watering every 10 days like clockwork. That's what I'd read online. But here's the thing: ZZs store water in their rhizomes. They need the soil to dry completely between waterings. In my apartment's humidity (45-50%), 10 days wasn't nearly enough drying time.
I bought a $12 moisture meter from Amazon. The soil was still damp at 2 inches deep on day 10. I pushed to 21 days between waterings. After 4 weeks, I saw two new shoots pushing up through the soil. No more yellowing since.
The fix was literally: wait longer. No fertilizer, no repotting, no pest treatment. Just let the soil dry out completely. ZZ plants are drought-tolerant — they'll forgive you for forgetting more than they'll forgive you for overwatering.