If the lower leaves on your geranium have turned yellow, the first instinct is usually to water more or to feed it. For zonal geraniums (Pelargonium), that reaction often makes things worse, because these plants are built for sun, dry spells, and fast-draining soil.
This page walks through the usual causes in the order worth checking. For the full routine, see the geranium care guide.
Quick triage
Is the soil still wet days after watering?
Suspect overwatering or poor drainage.
Are the yellow leaves low on the plant, with stems stretched and sparse?
Suspect weak light.
Are the leaves crisp and the pot light and dry?
Suspect underwatering or a root-bound pot.
Are there spots or fuzzy gray patches?
Suspect a fungal problem, usually tied to damp foliage and poor airflow.
Overwatering and heavy soil
This is the most common cause. Pelargoniums store some water in their thick stems and prefer to dry out between waterings. Constantly wet soil starves the roots of air, and yellowing leaves, soft stems, and a mushy stem base follow. Water only when the top of the soil has dried, make sure the pot drains freely, and empty the saucer. If the roots are already brown and soft, the page on root rot covers what to do next.
Not enough light
Geraniums are sun lovers. In dim rooms they grow tall and thin, drop lower leaves, and flower poorly. Move the plant to the brightest window available, ideally one that gets direct sun for part of the day, or add a lamp. The guide to grow lights for houseplants can help in dark winters, and leggy plants explains the stretching.
Underwatering or a root-bound pot
Geraniums tolerate dry soil better than wet soil, but a plant that is left bone dry for long stretches will still yellow and crisp at the edges. If water runs straight through the pot, or roots circle the surface, the plant may need repotting into the next size up with fresh mix. The article on overwatering and underwatering helps tell the two apart.
Fungal problems and poor airflow
Wet leaves, crowded stems, and stagnant air encourage gray mold (botrytis) and leaf spots. Water at the soil rather than over the foliage, remove fallen or dead leaves and spent blooms promptly, and give the plant room so air can move around it. Cut away affected leaves with clean scissors.
Nutrient imbalance
A plant that has been in the same soil for a long time may run short of nutrients, and one that is fed too heavily can build up salts that burn leaf edges. Feed lightly during active growth, following the label, and flush the pot with plain water now and then so salts do not accumulate.
A few things people ask
Is it normal for a few lower leaves to yellow?
Yes. Older leaves at the base naturally yellow and drop over time. It becomes a concern when many leaves yellow at once or the stems turn soft.
Should yellow geranium leaves be cut off?
Yes. Remove them along with any spent flowers, since decaying material invites mold.
Can a yellowing geranium recover?
Often yes, if the cause is corrected early. Fix the watering and light first, then give it a few weeks to push new growth.
Are geraniums safe around pets?
The ASPCA lists geranium as toxic to dogs, cats, and horses. See the ASPCA geranium page and keep the plant out of reach.
For the full routine that keeps blooms coming, see the geranium care guide.