Help, I've had my zz plant for about a year. The other week I changed pots, and now I just noticed a yellow leaf. What should I do? Water it more? I've been waiting for it to dry out before watering it, then I give it a good dose of water. Do you think it's because I repotted it? Thanks for the help!
An ancient aroid from Africa, as a general rule Zamioculcas zamiifolia (thus the ZZ) can do with little water. It does however enjoy more water in the summer months, far less in winter. Your potting mix should be very quick draining and contain some sand. It should never remain "muddy". If you used "off the shelf" potting soil that may be a part of your problem. The plant will not tolerate "wet feet" for long periods of time. It is best to mix the soil yourself using a good potting soil such as a "moisture control" type, extra peat, sand, and a good helping of Perlite™. I personally add orchid potting media to keep the soil quite loose. The charcoal in a good orchid mix will also keep the soil "sweet". In West Africa this species grows in very sandy soil. They do receive a summer rainy season, but the majority of the year is dry. By the way, I found a note on this board saying Zamioculcas zamiifolia is a Philodendron. It is not. Since it is an aroid, it is a member of the larger group known scientifically as Araceae. Many tropical species are members of that large group including Philodendron sp., Anthurium sp., Alocasia sp., Colocasia sp. and quite a few others. So Zamioculcas zamiifolia is a relative, but a very distant relative. The "ZZ" plant grows in distinctly different conditions than most other aroids. What makes scientists put it in this group is the plant produces a spathe and spadix like all aroids. There is a good discussion of this species on this board at this location: http://www.botanicalgarden.ubc.ca/forums/showthread.php?t=27137&highlight=Zamioculcas+zamiifolia
When you say you let the plant 'dry out', in terms of time, how often, more or less, are you watering at the moment? To give you an idea, mine has gone about a month and a half between waterings. Now that summer has finally arrived ( it was 'Spring' until last week) it will probably need water once a month. Sometimes we think the plant has dried out, and it hasn't in fact. Then, it could be from repotting it. It has happened to me with some plants that upon repotting them some leaves turn yellow and die, but I don't know why.
I grow my "ZZ" in a tropical atrium. As a result, it is watered at almost the exact same rate as all the tropical species which is 4 to 6 times a week. Now I can just hear the "screams" out there! Yes, I know that is far more water than this species normally needs and more than retailers recommend. However, I have it in extremely fast draining soil with lots of extra peat, Perliteâ„¢, sand and other media to keep the roots from sitting in water. During the winter, I avoid watering it for several weeks at at time. However. my method may not work for you, or most people, unless the soil is properly prepared. Regular potting soil just won't work. I suggest, provided you have it in a soil mix that drains very quickly (soil, sand, Perliteâ„¢, orchid potting media), water once a week in the summer and once a month in the winter. That would approximate the conditions this species receives nature. But the key is the soil! It must be fast draining! You are correct, it is quite normal for plants to loose leaves when repotted due to stress. But if the plant continues to decline then something else is wrong. I have read all sorts of suggestions and claims on this species but my goal with all the plants I grow, and I have well over 300 species, many very rare, is to mimic the plant's natural conditions. I don't treat plants as if they are "house plants", I treat them as if they are in their natural domain. I cannot emphasize enough the importance of mixing your soil to make certain the roots do not sit in mud. This aroid does not like wet roots! But as long as the soil drains very quickly the plant will prosper, even with frequent water. And I water very often. Mine is living proof!