How to tell
Too much direct sun. Dry brown patches or scorched edges show up where strong sun hits the leaf. ZZ plant does better out of harsh midday sun.
Tap-water salts (a smaller factor here). ZZ plant tolerates tap-water minerals better than more sensitive foliage plants (calatheas, prayer plants), so this is rarely the main cause. Salts can still build up in a mix that’s never flushed, though.
Fertilizer burn (easy to cause on this plant). Brown tips appear with a white crust on the surface. ZZ plant needs so little feeding that a normal houseplant dose is often already too strong for it.
Dry air (low humidity). Just the very tips and edges go brown and papery while the rest of the leaf is fine. This is most common in winter with the heating on, and ZZ plant prefers 30–60 % humidity.
Occasional dry spells (a minor factor here). Because ZZ plant goes long stretches between waterings by design, the very oldest leaf tips can dry and brown even with correct care. This is a much smaller factor than on thirstier plants and rarely the main cause.
