Geranium plant leaves turning yellow?
On outdoor geraniums, one or two oldest lower leaves yellowing can be normal, but widespread yellowing usually means wet roots, dry heat, nutrient loss, cold injury, or a pest or disease.
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The causes in full
Waterlogged soil or poor drainageMOST COMMON
How to tell
The soil 2 inches down feels waterlogged or stays damp for days, and the oldest lower leaves yellow first or the whole plant looks pale after rain or frequent watering.
What to do
Do not water while the soil 2 inches down is damp or waterlogged; wait until the soil 2 inches down feels dry before watering again. Pull mulch back from the stems, redirect runoff, and improve drainage around the bed if puddles linger.
Dry soil and heat stressCOMMON
How to tell
The soil 2 inches down feels dry or baked, leaves may droop before yellowing, and the damage is worse after scorching days or on the afternoon-sun side.
What to do
If the soil 2 inches down feels dry, water slowly at the base so the bed actually rewets instead of shedding water. During a heatwave, temporary afternoon shade cloth is okay, but keep the plant in full sun outside extreme heat.
Nutrients washed out or low fertilityCOMMON
How to tell
Yellowing builds slowly, often starting with older lower leaves, especially after repeated rain or in poor sandy soil, while the soil is not constantly waterlogged.
What to do
Feed with a balanced garden fertilizer at the label rate; do not add extra because excess fertilizer can burn roots. If the soil 2 inches down feels dry, water at the base after feeding; if it is damp, wait to water.
Cold snap or light frost injuryLESS COMMON
How to tell
Yellowing or pale, limp patches appeared right after a cold night, often on the newest tips or the most exposed side of the plant.
What to do
Do not fertilize or hard-prune immediately; wait a few days, then trim only clearly dead leaves and stems. Water only when the soil 2 inches down feels dry, because cold-damaged roots are easy to overwater.
Geranium rust or leaf spot diseaseLESS COMMON
How to tell
Look closely for small yellow spots, brown or rusty dots on leaf undersides, or spotted leaves that spread after wet weather.
What to do
Remove the worst spotted leaves and throw them away, and avoid wetting the leaves when you irrigate. Water at the base only when the soil 2 inches down feels dry, and space or thin crowded plants for better airflow.
Spider mitesLESS COMMON
How to tell
Leaves look finely speckled yellow, and you may see tiny moving dots or fine webbing on the undersides, especially in hot dry weather.
What to do
Rinse leaf undersides in the morning to knock mites off, then use a labeled insecticidal soap or horticultural oil if mites remain. Keep soil watering on the same rule: water the bed only when the soil 2 inches down feels dry.
Will it recover?
Yellow geranium leaves usually do not turn green again; the goal is to stop the cause and watch for healthy new green growth.
Stopping it happening again
Grow geraniums in full sun with good airflow and drainage, and water only when the soil 2 inches down feels dry.
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