How often to water ZZ plant

The interval

A ZZ plant is watered about every 18 days in the growing season and about every 35 days in winter, and only once the compost is dry all the way through. The growing season is spring to early autumn wherever you live, so the northern and southern hemispheres sit on opposite halves of the calendar, and a ZZ in a dark room grows slowly. The NC State plant toolbox suggests about twice a month in summer and once a month in winter, provided the soil has dried out completely. The entry's intervals sit a little longer than that, and in both cases the compost decides.

Lift the pot. This is the best check, because the plant stands in compost that can stay damp at the bottom long after the surface is dry. A pot that needs water is noticeably light, and one that still feels heavy a week after the interval is up is not ready. A finger pushed to the bottom of the pot, or a gentle look at the rhizomes, is the second check. The Royal Horticultural Society's advice is to allow the compost to dry out completely and to err on the side of underwatering.

An overwatered ZZ turns yellow at the bottom first. The lower stems yellow, the base goes soft, and the compost smells sour as the rhizomes rot. A thirsty one gives very few signs and gives them late, because the fat underground rhizomes carry weeks of reserve and the plant will wait months rather than complain.

Soak and dry means a proper soak. Pour slowly over the compost until water runs freely from the drainage holes, let it drain completely and empty the saucer. Do not give small drinks in between. The RHS says average household humidity is adequate, so misting is no help.

The thing particular to this plant is what is under the compost. The rhizomes look more like potatoes than roots, and they are what rots. If you are unsure, wait, because doing nothing is nearly always the safer choice.

Related guides

How to tell whether a plant actually needs water

The finger, the weight, the leaf and the pot. Four ways to read a plant's thirst, and what overwatering actually is.

Rescuing an overwatered plant

How to tell overwatering from underwatering, how much root damage is recoverable, and the exact rescue steps once compost has stayed wet too long.

Watering through a southern winter

Winter in the southern hemisphere runs June to August, and houseplants drink far less then. How to read the soil, and why overwatering is the bigger risk.