Why does my ZZ plant have yellow lower leaves?

On a ZZ plant this shows as the lowest stems turning yellow, usually starting with the leaflets at the base and working up, until the whole stem is yellow and falls over. The stems higher up and in the middle of the plant stay glossy and green.

The most likely cause is too much water. The entry says that yellow lower leaves on this plant are almost always overwatering, and the beginning of rhizome rot. Under the compost are fat rhizomes that store water, which is why the plant waits months rather than complain. It is watered about every 18 days in the growing season and about every 35 in winter, and a pot kept on the summer rhythm in winter, or watered in small amounts often, keeps the rhizomes sitting in damp compost.

To confirm it in a minute, lift the pot and push a finger as deep into the compost as it will go. Damp at the bottom and heavy days after watering is your answer. Then dig gently beside the stem and feel a rhizome. Firm and plump means you can dry the pot out. Soft, brown and sour smelling means rot has started and the damaged parts must be cut away.

Two other causes are worth ruling out. One old stem at the outside turning yellow while the rest of the plant is healthy and pushing up new stems is simply the plant retiring a stem. And a very dim spot, with the plant standing well back from the window, can bring on yellowing from the bottom over several weeks, because a plant cannot pay for leaves it cannot light.

A yellow stem does not recover, and a ZZ in low light makes only a couple of new stems a year, by the entry's account, so judge the recovery over a season, not a fortnight. Once the compost has dried, the plant should stop shedding stems, and new ones come up from the rhizomes in the growing season.

What this plant wants

The fix

Stop watering, check the rhizomes are firm rather than soft and brown, and cut away any that have gone. Let the compost dry completely before the next drink.

Read on

Yellow leaves at the bottom of the plant

The same sign on any plant, with the causes in the order they are likely.

ZZ plant care

Light, water, feeding, repotting and the rest of the entry.

Check it in the diagnoser

Opens with the plant, the part and the sign already chosen.