Zonal geranium spots on leaves: causes and what to do
8 results in the diagnosis tree begin with spots on the leaves, 5 of them marked likely when the answers fit. They are ordered here for Zonal geranium (Pelargonium zonale), using what its sources say about light, soil moisture, humidity and pests and diseases and 3 problems recorded for it.
Sources last read 18 September 2026.
Pelargonium zonale is a species of Pelargonium native to southern Africa in the western regions of the Cape Provinces, in the geranium family. It is one of the parents of the widely cultivated plant Pelargonium × hortorum, often called "geranium", "horseshoe geranium", "zonal geranium" or "zonal pelargonium". Wikipedia, CC BY-SA 4.0
Native range: Cape Prov. to KwaZulu-Natal (subtropical). Also sold as horseshoe geranium and zonal pelargonium.
What Zonal geranium’s sources say that bears on this
- Light
- Full sun, Partial shadeRHS · read 13 September 2026
- Soil moisture
- Well-drainedRHS · read 13 September 2026
- Humidity
- ASHRAE recommends indoor relative humidity between 30% and 60%Penn State Extension · read 13 September 2026
- Pests and diseases
- Aphids, fungus gnats, thrips, caterpillars, leafhoppers and vine weevil can attack it. Disease risks: a virus, Pelargonium rust, grey moulds, and root and foot rots where soil is wet.RHS · read 13 September 2026
How this shows up on a Zonal geranium
Bleached patches on the side facing the glass
On a zonal geranium the marks are patchy and one-sided. Leaves on the shaded side of the plant keep their colour entirely.
Glass concentrates what would be tolerable outdoors, because it holds the heat and removes the moving air that carried it away. Its source describes full sun, partial shade.
Telling it apart: Whether the undersides are affected. Light damages what it reaches and nothing else.
RHS · read 13 September 2026Gray, furry patches on damaged or dying leaves
Patches of the zonal geranium turn soft and collapse under a gray, velvety coating.
RHS lists gray mold among the diseases it may get. Gray mold (botrytis) enters through damaged or dying tissue and spreads in cool, humid, still air.
Telling it apart: The texture. Tissue under gray mold is soft and rotting; sun scorch is dry.
RHS · read 13 September 2026Orange, powdery pustules under the leaves and pale spots above
The undersides of the leaves of the zonal geranium carry raised, powdery orange spots that leave color on a fingertip.
RHS lists rust among the diseases it may get. Wet leaves and humid, still air let it infect and spread.
Telling it apart: Rub a pustule. Rust leaves orange powder on the finger; a leaf spot does not.
RHS · read 13 September 2026Possible causes, likeliest first for a Zonal geranium
Most likely spider mites
Why: Spider mites feed on individual leaf cells, and each emptied cell shows as a pale speck.
What to try:
- Move the zonal geranium away from other plants.
- Wash the leaves, top and underside, with a strong spray of water in a shower or sink.
What would settle it: Hold a sheet of white paper under a leaf and tap the leaf. Tiny specks that move across the paper are mites.
Most likely powdery mildew
Why: A white coating that wipes off is the surface growth of a fungus.
What to try:
- Remove the worst-affected leaves.
- Improve air movement around the zonal geranium and space it away from others.
What would settle it: Wipe a patch. Powdery mildew comes away and leaves a yellowed patch beneath. White that does not wipe off is part of the leaf, or a mineral deposit from hard water.
Most likely thrips
Why: Thrips rasp the leaf surface and drink what leaks out, which leaves silvery, papery streaks.
What to try:
- Move the zonal geranium away from other plants.
- Wash the leaves thoroughly and remove badly damaged ones.
What would settle it: Tap a leaf over white paper. Thrips are slender, fast-moving and about the size of a comma; they are easy to see once they are on paper.
Less likely for a Zonal geranium, still possible
Questions
- What usually causes spots on the leaves on a Zonal geranium?
- For Zonal geranium: spider mites, powdery mildew and thrips.
- How can I tell which one it is on my Zonal geranium?
- What do the marks look like? Pale, dry, bleached patches on the side facing the window; Brown or black spots, many with a yellow ring around them; Tiny pale speckles all over, sometimes with fine webbing underneath; A white powdery coating that wipes off; Silvery streaks with tiny black dots; Dark, soft, water-soaked patches.
- What do Zonal geranium's sources say about its light?
- RHS: Full sun, Partial shade.
- What does this look like on a Zonal geranium?
- On a zonal geranium the marks are patchy and one-sided. Leaves on the shaded side of the plant keep their colour entirely. Telling it apart: Whether the undersides are affected. Light damages what it reaches and nothing else.
- Is Zonal geranium safe to handle while I check it?
- Its sources list it as toxic to cats and dogs. Wash your hands after handling the roots or sap, and keep trimmings away from pets.
Other plants that show spots on the leaves
African violetFuzzy gray growth over spreading patches on leaves and stems
Barberton daisyDark spots with a yellow halo spreading across the leaves
Bearded irisFuzzy gray growth over spreading patches on leaves and stems
Bigleaf hydrangeaBrown or black spots on the leaves that grow and merge
Blue passion flowerBleached patches on the side facing the glass
Busy LizzieAngular pale patches and a downy coating on the undersides
Something else wrong with the Zonal geranium?
What this does not cover
This page orders a decision tree's results using a plant's sourced care. It has not seen your plant, its pot or its window, and two problems at once are common: that is the usual reason a confident answer turns out wrong. The questions in the diagnosis tool narrow it further than a list can.