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How to treat Geranium with yellowing leaves?

I’m hoping someone can help me please. All of my Geraniums (or maybe they’re Pelargoniums - I don’t really know the difference) have these yellowing patches on some of the leaves.
I have treated them with Liquid

Copper Fungicide and also Eco Fungicide (not at the same time).
They’re also being attacked by caterpillars so have also been treated with Dipel and Eco Pest Plus.

They’re quite sentimental so I’d really like to be able to save them. I’d appreciate any advice please. Thanks so much

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Comments

MitchellMc

Welcome to the Bunnings Workshop community @alibee. It's terrific to have you join us, and many thanks for your question about plant care.

You've done a great job covering the basics—treating with fungicide and using Dipel for caterpillars are both excellent steps. Since you've already addressed the most common pest and fungal issues, the next area to investigate is the plant's growing conditions, particularly the potting mix and watering routine. Yellowing leaves can be a sign of both overwatering and underwatering, so it's important to ensure your geraniums are in a high-quality, free-draining potting mix. If the mix is old, compacted, or retains too much moisture, it might be worth repotting with fresh mix.

Also, make sure the pots have proper drainage and that water flows out easily when watering. If the water pools or drains slowly, it could be causing root stress. Adding a layer of small stones at the bottom of the pot before the potting mix can also help improve drainage. Geraniums prefer the soil to dry out slightly between waterings, so it's best to wait until the top layer of soil feels dry before watering again. If you can share more about your current watering habits and how quickly the soil tends to dry out, we can better determine whether moisture levels are contributing to the issue.

Please let me know if you have any questions.

Mitchell

alibee

https://www.workshop.bunnings.com.au/discussion/comment/52858#Comment_52858

Thanks so much @MitchellMc I appreciate you replying.

All the geraniums are in terracotta pots. I water when the top 2cm of soil has dried out. I don't have saucers under them and they sit on small tiles which acts as pot feet. There is just the single hole at the bottom of the pot as is standard in terracotta pots.

They are in Osmocote Premium potting mix with some extra perlite mixed in. I only repotted them about 6 months ago. Since then I have given them regular seasol and have recently given them a dose of Charlie Carp.

I have just pulled this Geranium out to inspect the roots. They are still damp from me washing the soil off in this photo. They seem firm and don't smell which I think might mean they're not rotting. I am a bit worried that it might be Geranium Bacterial Blight but I'm hoping you can reassure me. Geranium roots 31st May 2025.jpg I

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/88614#Comment_88614

Thanks so much for the update @alibee, and for going to the effort of checking the roots—that’s really helpful. From what you’ve described, your care routine sounds excellent. Using terracotta pots with no saucers, quality potting mix with added perlite, and watering only when the top layer is dry is exactly what we’d recommend for healthy geraniums. Your fertilising schedule also sounds well balanced.

It's great news that the roots are firm and healthy-smelling. That makes root rot less likely and suggests your plants are coping well below the surface.

Based on your photos and description, it’s unlikely to be Geranium Bacterial Blight, which usually causes more aggressive symptoms—wilting, sudden leaf collapse, blackening of stems, and often a slimy appearance. Your plants don’t seem to be exhibiting those signs. Instead, the yellowing patches you're seeing could be the lingering effects of stress—possibly from earlier caterpillar damage or some temporary environmental stress like windburn, fluctuating temperatures, or inconsistent moisture from pooled water around the pots.

I’d recommend trimming off the affected leaves so the plant can redirect energy to new, healthy growth. Keep an eye on whether new leaves continue to develop with similar issues. If not, it was likely just a transient issue. If new leaves are also affected, we can dig a little deeper into potential nutrient imbalances or rare fungal/bacterial causes.

You’re clearly taking excellent care of these plants, and your attention to detail is giving them the best chance to thrive.

Mitchell

alibee

https://www.workshop.bunnings.com.au/discussion/comment/109993#Comment_109993

Thank you so much @MitchellMc I feel very reassured! Does that mean I should stop treating with eco-fungicide and just see how it goes.

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/122351#Comment_122351

I'm not seeing any signs of fungus, so since you've already treated them, I wouldn't continue with it @alibee.

One thing to consider, especially if you’re starting to see frost in your area, is that cold temperatures can cause leaf yellowing and patchiness. Geraniums and pelargoniums are frost-sensitive, and even light frosts can damage their foliage. The leaves may show discolouration, become soft or water-soaked, or develop a bleached or scorched appearance after exposure. That might be what you're seeing here.

Mitchell

alibee

https://www.workshop.bunnings.com.au/discussion/comment/130300#Comment_130300

Good point. Thanks @MitchellMc I'll keep an eye out. You have been incredibly helpful. Thank you so much!

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/135243#Comment_135243

It's my pleasure, @alibee.

Mitchell

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