Newsletter Articles
Why Does My Geranium Have Spots on Its Leaves?
By Richard Flowers, ACCNP-Green Thumb Nursery-Ventura
Spots on geranium leaves usually trace to one of a few specific causes, and they are not all the same problem. The usual culprits are rust, edema (corky bumps from overwatering ivy geraniums, which is not contagious), and bacterial leaf spot, each managed mainly by watering at the base, improving air flow, and removing affected leaves.
Quick answer: Look at what the spots look like and where they are to find the cause.
- Rust-colored pustules on the underside, with yellow specks on top, point to geranium rust, a contagious fungus.
- Corky white, pale, or tan bumps and patches on the underside of ivy geranium leaves point to edema from overwatering, which is not a disease and does not spread.
- Water-soaked or V-shaped brown lesions point to bacterial leaf spot, so remove those plants promptly.
- Water at the base, never overhead, and space plants so leaves dry quickly.
- Remove affected leaves, clean your tools, and start with healthy plants to stop spread.
| Cause | Looks like | What to do |
|---|---|---|
| Geranium rust (fungus, spreads) | Yellow specks on top, rust-colored pustules underneath. | Remove affected leaves, avoid overhead watering, keep tools clean. |
| Edema (overwatering disorder, does not spread) | Pale, white, or tan corky bumps and patches under the leaf, common on ivy geraniums. | Water less and improve light and air flow; it is not contagious. |
| Bacterial leaf spot (bacteria, spreads) | Water-soaked spots and V-shaped lesions from the leaf edge. | Remove and dispose of infected plants, water at the base, sanitize tools. |
| Botrytis gray mold (fungus, cool and damp) | Brown leaf spots, often where faded petals have fallen. | Remove spent flowers and leaves, improve air flow, water early in the day. |
What the Spots Are Telling You
Spots on a geranium come from just a few causes, and the first job is to tell a contagious disease apart from a harmless watering disorder. Rust, bacterial leaf spot, and botrytis are living infections that spread from plant to plant, so they call for prompt removal and sanitation. Edema is different: it is a physiological response to too much water, not a pathogen, so it does not spread and is fixed by changing how you water. The sections below walk through each one, and for the geranium budworm caterpillar, which chews buds and flowers rather than spotting leaves, see our guide to geranium budworm.
Rust and Bacterial Leaf Spot: the Diseases
Rust and bacterial leaf spot are living infections that spread between plants, so catching them early matters. The Connecticut Agricultural Experiment Station describes geranium rust as small yellow spots on the upper leaf surface with rust-colored pustules developing in those spots on the underside.[1] Penn State Extension describes the same pattern, with chlorotic specks on top directly opposite pustules of rust-colored spores below.[2] Bacterial leaf spot looks different: Penn State Extension notes small water-soaked spots that become sunken, plus V-shaped yellow areas with the wide part of the V at the leaf margin and the point toward a vein.[3] Both spread, so the Connecticut Agricultural Experiment Station advises removing symptomatic plants promptly, avoiding overhead irrigation, and keeping tools and benches clean.[1] For broader plant-health habits, see our guide to organic pest control.
Edema: Too Much Water, Not a Disease
If the bumps are corky and sit on the undersides of ivy geranium leaves, the cause is usually edema, a watering disorder rather than an infection. Penn State Extension describes small, pale, translucent, watery pustules on the leaf underside, which can look like whitish patches at first, that then enlarge, turn brown, and become corky or scabby.[4] Iowa State University Extension is explicit that this is not caused by an insect or disease pathogen; it is a physiological problem that occurs when plants absorb more water through their roots than they transpire through their leaves.[5] Because it is a watering imbalance and not contagious, Iowa State University Extension says it can be minimized by not over-watering during cloudy weather and reducing humidity.[5] Our guides to water-wise watering and your yard’s microclimates can help you dial in water and air flow.
Preventing Spots on Geraniums
Most geranium leaf problems are prevented by the same handful of habits. Penn State Extension and the Connecticut Agricultural Experiment Station both recommend watering in a way that keeps leaves dry, spacing plants for good air circulation, removing spent flowers and infected leaves, and sanitizing tools and pots.[2] Those same steps limit botrytis gray mold, which the Connecticut Agricultural Experiment Station notes forms brown leaf spots in cool, damp conditions, often where faded petals land on leaves.[1] University of California IPM adds that because water is necessary for rust infection, overhead irrigation should be avoided when rust is a problem.[6]
Still not sure what is spotting your geraniums? Bring a leaf sample to any Green Thumb Nursery and our team can help you identify the cause and the right next step.
Geranium Leaf Spot FAQ
Why does my geranium have brown spots on its leaves?
Usually rust or bacterial leaf spot. The Connecticut Agricultural Experiment Station describes rust as rust-colored pustules under the leaf, while Penn State Extension describes bacterial leaf spot as water-soaked, sunken spots with V-shaped lesions.[1]
What are the white or corky tan patches on my ivy geranium leaves?
That is almost always edema, not a disease. Iowa State University Extension explains edema is a physiological problem from the plant absorbing more water than it transpires, and it is not caused by an insect or pathogen.[5]
Is geranium rust contagious?
Yes, it is a fungus that spreads between plants. Penn State Extension recommends removing infected leaves and not irrigating overhead, since water is needed for the spores to infect.[2]
Are spots on geranium leaves caused by overwatering?
The corky edema bumps are. Iowa State University Extension notes edema can be minimized by not over-watering during cloudy weather and reducing humidity, which points to a watering fix rather than a spray.[5]
How do you prevent spots on geraniums?
Keep leaves dry and clean up. The Connecticut Agricultural Experiment Station recommends avoiding overhead watering, spacing plants for air flow, removing symptomatic leaves, and sanitizing tools and benches.[1]
Sources
- [1] Connecticut Agricultural Experiment Station, Diseases of Geranium: portal.ct.gov
- [2] Penn State Extension, Geranium Diseases: extension.psu.edu
- [3] Penn State Extension, Bacterial Blight of Geranium: extension.psu.edu
- [4] Penn State Extension, Edema of Geranium: extension.psu.edu
- [5] Iowa State University Extension, Blister Growths on Ivy Geranium Leaves (Oedema): yardandgarden.extension.iastate.edu
- [6] University of California IPM, Rust (Floriculture and Ornamental Nurseries): ipm.ucanr.edu
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