How Often to Water a ZZ Plant: Once a Month in Winter, and Why That Is Allowed

This site does not give watering schedules, and for one plant it will. Three extension services, NC State, Clemson and UConn, publish a frequency for the ZZ plant, and they agree on it because the honest number is so small that a calendar cannot do much harm: how often to water a ZZ plant comes out at once or twice a month, once in winter, and only ever on a day the soil is completely dry. The Zanzibar gem, as the shops sometimes label it, is the plant people kill by treating it like the pothos next to it.

The short version

1. Once a month in winter, twice in summer. NC State's figures; Clemson says one to two times a month. Both attach the condition that the soil is completely dry first.
2. It is a rhizome with leaves on it. The water is stored underground, which is why the schedule can be that sparse.
3. Yellow leaves mean it was watered like a normal plant. One extension service calls overwatering just about the only thing that kills it.
4. Low light is fine; direct sun is not. It grows under office lights and scalds in a south window.
5. Slow is the design. Feed it once or twice a year and stop expecting growth from it.

Why this plant gets a number when others do not

The rule on this site is to water on evidence rather than on a schedule, because a schedule cannot know how much light a pot is getting or how fast it is drying; the reasoning is in overwatering vs underwatering. A ZZ plant is the case where the rule and a schedule stop disagreeing, because the schedule is so sparse that the evidence has nearly always caught up with it.

The reason is underground. NC State describes the plant from the bottom up: It has bulbous fleshy rhizomes that give rise to glossy leaves that store water and make it highly drought tolerant. UConn says the same thing from the stem's point of view, The stems thicken at the bottom as they arise from starchy rhizomes, and draws the conclusion: Because of their fleshy rhizomes, ZZ plants can store a fair amount of water.

So the number is not a shortcut. It is what the evidence rule produces for a plant whose reserve is measured in weeks: check the soil, find it dry, and even then the plant is probably fine for a while yet.

How often to water a ZZ plant, from the sources

NC State gives two figures and one condition. Winter: Water it only once a month in winter months when it is not actively growing. Summer: Water twice monthly in the summer, but only if the soil has dried out completely. The reason for the condition is in its potting advice, which ends as wet feet are not tolerated.

Clemson lands in the same place without splitting the year: Water 1-2 times a month, only after the potting medium has completely dried, and Do not allow the plant to sit in water. UConn does not give a number and gives the rule that generates one: Plants should be watered sparingly, and When in doubt about whether to water or not, err on the dry side.

Read the condition as the rule and the frequency as its ceiling. In a dim room in winter, a pot that has not dried out by the end of the month does not get watered because the month has ended. In a bright room in July, NC State's twice a month is the most it should ever need, not a target.

ZZ plant yellow leaves: overwatered vs underwatered

Yellow leaves on a ZZ plant are, nearly always, the plant reporting that it has been watered like something it is not. UConn puts it as flatly as an extension service ever does: Overwatering is just about the only factor that leads to the demise of this tough houseplant. And the signs: Signs of overwatering are yellow leaves and rotting rhizomes.

The overwatered-versus-underwatered question, which is a real question for most houseplants, is a lopsided one here. Underwatering a ZZ plant takes months of neglect, and the rhizomes shrivel before the leaves show much. Overwatering takes a few weeks of ordinary good intentions. There is a third reading, and it is the one that gets missed.

The light reading comes from UConn as well: Leaves exposed to too much light may yellow and then brown, and before that, Too much direct light will cause scalding (a whitening) of leaves and leaves may curl. A yellow ZZ plant on a south sill with dry soil has been scalded rather than starved, and watering it adds the first problem to the second.

What to do with the common case is the same as for any rotting plant, and it is in overwatering vs underwatering: stop, let it dry completely, and if stems are soft at the base, tip the pot and cut away any rhizome that is brown and mushy rather than firm. The plant's reserve is what makes recovery plausible; a ZZ with one firm rhizome left can rebuild.

Does a ZZ plant need sunlight?

Not direct sun, and less light than almost anything else you could buy. NC State: While they will grow in very low levels of light, even in areas with only fluorescent light, they do best with bright indirect sunlight. The other end is firm: Scalding and browning of leaves can occur if the plant is placed in direct sunlight. Clemson makes it one instruction: Locate ZZ plants anywhere except in full sunlight.

UConn allows one exception and names the extreme case: ZZ plants will not tolerate direct sunlight except perhaps an eastern exposure during the winter months, and They are even suited for a windowless office as long as exposed to fluorescent lights for several hours each day. For a rented room with a north window and a building across the street, that is the whole list of plants that does not mind, and this one is on it. The light estimator will tell you which band your spot is in; for a ZZ plant, any band but the top one is workable.

Then the observation only one of the three sources makes, and the one worth showing a child: UConn notes that Also stems may change positions to bend away from the light which is the opposite of how most plants behave. Most houseplants lean toward the window. A ZZ plant leaning away from the window is a plant from open woodland doing what it does, and one more reason the sill is the wrong place for it.

Slow is the design

A ZZ plant that has not grown all year is probably fine. NC State: This plant has a slow growth rate, reaching 2 to 4 feet in height and width. UConn adds the indoor qualifier: Plant growth is much slower in lower light conditions found in many homes. Clemson says bright indirect light will speed up its very slow growth rate, which is a sentence with the emphasis in the right place.

Feeding follows from that. NC State: Use a balanced liquid houseplant fertilizer once or twice a year. Clemson: ZZ plants are slow-growing and should be fertilized only once or twice during the growing season with a balanced fertilizer. Anything more sits in the soil, for the reasons in fertilizing houseplants.

Propagation is slow too, and it works: UConn suggests, If you would like to make more ZZ plants, try rooting some leaf cuttings, with the honest timescale that More typically under indoor household conditions it may take up to 9 months for the rhizome to start to form. The method, and why soil beats a jar, is in how to propagate houseplants.

One more thing that looks wrong and is not. Clemson, on the stems: A stem with normal black spots indicates a typical, healthy ZZ plant.

Light, water, and the cat

For the plant's card in The Windowsill, the game on this site: low to medium light, never direct sun; water once or twice a month (NC State, Clemson) and only when the soil is completely dry; no humidity requirement worth building; and the slowest grower in the shop.

On pets the sources are less reassuring than for the spider plant or the fern. NC State rates it: This plant has a medium toxicity to cats and dogs. UConn gives the reason and the precaution: Many members of this family contain calcium oxalate crystals which can be extremely painful and damaging to soft tissues in the mouth and throat, so As a precaution, make sure plants are not in areas where small children or pets might be able to sample them. The ASPCA's database, which the site's toxicity table uses for every other plant, has no entry for the ZZ plant; the pet rating here rests on NC State, and the human rating NC State also publishes is a separate figure that is not the one quoted above.

Common questions

How often to water a ZZ plant? NC State says once a month in winter and twice monthly in summer, only if the soil has dried out completely; Clemson says one to two times a month after the potting medium has completely dried. Treat the frequency as a ceiling and the dry soil as the rule.

Why are my ZZ plant's leaves turning yellow? Most often overwatering, which UConn calls just about the only thing that kills this plant; yellow leaves with rotting rhizomes are its two signs. If the soil is dry and the plant sits in direct sun, the yellowing is scald instead, and the fix is shade rather than water.

Does a ZZ plant need sunlight? Indirect light, and it will manage on fluorescent light alone; direct sun scalds it.

Why is my ZZ plant not growing? Because it is a slow plant in a dim room, which is the normal case. NC State describes the growth rate as slow, UConn says it is much slower in the low light of most homes, and Clemson says bright indirect light speeds up a very slow rate rather than turning it into a fast one. New stems come a few a year in good light and fewer in poor light. A ZZ plant that is not growing and not yellowing is doing exactly what the sources describe.

Is a ZZ plant toxic to cats? NC State rates it as a medium toxicity to cats and dogs, and UConn advises keeping it where pets and small children cannot sample it, citing the calcium oxalate crystals common to its family. The ASPCA has no entry for it, so there is no ASPCA rating to give.

One thing to do this month

Write the date of the last watering on a strip of tape on the pot.

Then do not touch the watering can for that plant until the month has turned, and on the day it turns, check the soil before you decide. The tape exists to stop you, not to remind you.