plantcarenotes.com

TL;dr
Bottom-up yellowing is almost always a result of being watered too much (roots staying wet) most often in low light.
Light stress can also appear from a move: too much sun can scald leaves, too little can indirectly cause yellowing by slowing drying.
Do 3 fast checks. Soil dryness, drainage, and changes in light recently. Then follow the fix that correlates.
If the base is mushy, the soil smells sour, or yellowing is spreading quickly, treat like early root/rhizome rot. Stop watering, then inspect and see if a repot into fast-draining mix helps.

What does “yellowing from the bottom up” usually signal for a ZZ plant

While they have rhizomes which hold water, ZZ plant, (Zamioculcas zamiifolia) does not prefer wet feet. The most typical scenario for a ZZ to decline in a home is staying wet for too long, especially in low light, giving the appearance of sacrificing the oldest leaves (lower) first, which we read as “yellowing from the bottom up.” (extension.umn.edu) . Eventually, it all leads to a mushy rotten mess.

That said, the bottom leaves can yellow from two other stressors that are easily confused with watering issues: (1) light shock (a big change in the level of light) and (2) normal aging of an older leaflet/stem, remaining firm and green while this is occurring.

Quick diagnosis: light stress vs watering mistakes (cheat sheet)

The 3-minute check: confirm the real cause before you “fix” anything

1. Check the soil below the surface: push a dry wooden skewer/chopstick to near the bottom, wait 10 seconds, then pull it out. If it’s dark/damp or has soil stuck to it, the root zone is still wet.
2. Check drainage reality (not just the label): confirm there’s a drainage hole, and that water can actually exit (no blocked holes, no hidden inner pot sitting in water inside a cachepot).
3. Replay the last 2 weeks: did you (a) water on a schedule, (b) repot into a heavier mix, (c) move it closer to a window, or (d) turn on stronger heat/AC? Those changes often explain the timing.
4. Inspect the yellowing tissue: mushy base and soft stems lean toward wet-root stress; crisp edges and papery texture lean toward drought/sun/heat stress. Look for a cue: One old stem = commonly normal aging; Several stems yellowing simultaneously = usually a root-zone problem.

Why the “below the surface” check matters: ZZ plants can show dry on the top and stay wet deep in the pot, particularly in low light or in dense mixes. Extension resources teach to let the potting mix dry out between waterings (and lean to the dry side) to avoid yellow leaves and rotting rhizomes in constantly wet conditions. (homegarden.cahnr.uconn.edu)

Fix watering problems (without guessing)

Most “mystery yellowing” on ZZ plants can be traced back to one main problem: roots sat wet too long. ZZ plants have rhizomes to hold water and can stand being dried out; they do not like to have “wet feet.” extension.umn.edu

• Watering on a calendar (ex. every Saturday) vs watering only when the pot is dry.
• Low light + normal watering: in dimmer spots the soil dries much more slowly, and the same amount/frequency is “too much.” ZZ will tolerate very low light, but generally performs best in bright, indirect light gardeningsolutions.ifas.ufl.edu.
• No drainage hole, or decorative pot (cachepot) that quietly holds runoff water.
• Dense/old potting mix that compacted and stays wet longer than it previously did.
• Winter watering at summer frequency: several extension resources recommend watering much less in winter since the plant is not actively growing and slow to dry plants.ces.ncsu.edu

Fix watering problems (without guessing)

1. Stop top-off watering. Wait until the pot is dry deep down (use the skewer test).
2. When it’s time, water thoroughly until water runs out of the drainage holes, then discard runoff so the plant doesn’t sit in water. (yardandgarden.extension.iastate.edu)
3. If the pot takes longer than ~3–4 weeks to dry in normal indoor conditions, treat that as a signal to increase light and/or repot into a faster-draining mix.
4. If yellowing is spreading and the soil is wet: unpot and inspect rhizomes. Healthy rhizomes are firm; rotting ones tend to be soft/mushy. Overwatering is specifically associated with yellow leaves and rotting rhizomes in extension guidance. (homegarden.cahnr.uconn.edu)

If it’s light stress: what it looks like and how to correct it safely

ZZ plants tolerate low light, but generally do best in bright, indirect light. Multiple extension and university resources also warn that direct afternoon sun can damage foliage (scalding/browning). (yardandgarden.extension.iastate.edu) Move back to bright indirect light (near a window, but out of direct rays). (yardandgarden.extension.iastate.edu)

1. If you want it brighter, acclimate: increase light exposure gradually over 1–2 weeks (especially if it was previously in low light).
2. Don’t “compensate” by watering more unless the pot truly dries faster—brighter light may increase drying, but only you can confirm that with the soil test.

Too little light: not always the direct cause, but invites watering failure

ZZ will survive in fairly low light (including fluorescent-only environments), but in a dark corner it dries slowly and grows slowly—so a “normal” watering routine can melt into chronically watering too often. UF/IFAS and NC State both note that ZZ tolerates very low light, yet does best in bright indirect light. (gardeningsolutions.ifas.ufl.edu)

• If your ZZ is a few feet from a window and the pot gets wet for a long time, increase light before you increase watering.
• A simple grow light is effective in a windowless room; the goal is never “full sun,” but steady, moderate light that helps the pot dry at a healthy pace. (Commercial guidance notes ZZ can persist in a low interior light for long periods.) (ask.ifas.ufl.edu)

Proposed rescue plan for failing leaf bottom (do in order)

1. Stop watering immediately if you have not checked below the surface; adding more H2O to a wet pot is the fastest way to a plant with yellowing leaves.
2. Get it into the right light today: bright, indirect light; avoid intense direct afternoon sun. (yardandgarden.extension.iastate.edu)
3. Confirm drainage: pot must have a working hole; don’t leave a pool in saucers/cachepots after watering. (gardeningsolutions.ifas.ufl.edu)
4. Decide whether to unpot: If several yellow stems, all stems, or stems that were green when you bought it yellowing quickly, whole-pot feels mushy, or only half a stem sticks up out of the pot, unpot and check the rhizomes. Extension guidance warns yellow leaves and mushy rhizomes indicate overwatering. (homegarden.cahnr.uconn.edu)
5. If you find rot: cut away mushy or blackened tissue cleanly with a clean blade, let the cut air-dry for a moment, then pot in a mix that drains well in a pot with a hole. Water lightly only when you feel the soil and mix are mostly dry.
6. Remove yellowing stems at the base. Clean pruners first, please. (Later: leaves that are mostly yellow tend not to re-green, so taking them off helps you track whether the center of the plant shrank.) You would keep doing this till you see some evidence of improvement.
7. Track for 2 weeks; track for 4: if you keep getting new yellowing, it means you still have a root-zone problem (too wet, too dense, too dark, or pot too large for the mass).

FAQ: ZZ plant yellowing from the bottom up