The two most common houseplant problems can look surprisingly alike from a distance. Here's how to actually tell them apart, and how to recover from each.
It's tempting to diagnose a struggling plant purely by how the leaves look, but the soil itself is the fastest, most reliable signal. Push a finger 1-2 inches into the soil (or use a cheap moisture meter). If it's consistently wet at that depth even a few days after the last watering, overwatering is the more likely culprit. If it's bone-dry and has been for a while, underwatering is more likely.
Overwatered leaves tend to turn yellow while still feeling soft, sometimes almost water-logged. You may also notice the stem feeling mushy or dark near the soil line, a sour or musty smell from the pot, or small gnats hovering around the soil surface (fungus gnats breed in consistently wet soil). In advanced cases, leaves can turn brown or black and simply collapse.
Underwatered leaves usually go the other direction texturally: they turn crispy and dry, often starting at the edges and tips before spreading inward, and they may curl or fold as the plant tries to reduce water loss. The whole plant can also look limp or droopy, but — unlike overwatering droop — it perks back up within a few hours of a thorough watering.
Stop watering immediately and let the soil dry out completely before resuming a more conservative schedule. If you suspect root rot has already set in, gently remove the plant from its pot and inspect the roots: healthy roots are firm and white or tan, while rotten roots are dark, mushy, and often smell bad. Trim away anything rotten with clean scissors, then repot into fresh, well-draining soil in a pot with drainage holes — reusing waterlogged soil just reintroduces the same problem.
Water thoroughly and slowly until it runs from the drainage holes, rather than a quick splash on top, which can run straight past dry, shrunken soil without actually rehydrating it. If the soil has pulled away from the sides of the pot, consider bottom-watering (setting the pot in a shallow tray of water for 20-30 minutes) so the whole root ball rehydrates evenly.
Most recurring watering problems come down to two fixable things: a pot without drainage holes, and watering on a fixed calendar instead of checking the actual soil. Every houseplant's ideal watering frequency depends on its pot size, the season, humidity, and light — a fixed "every Sunday" schedule works for some plants and slowly kills others. Checking the soil directly, every time, is the single habit that prevents the most houseplant deaths.
If you're not sure which way a specific plant is leaning, LeafRx's free diagnose tool can take a photo and help pin down which of the two is actually happening.