How to treat yellow magnolia leaf?

Help! I found one of the leaves of our potted white caviar magnolia turning yellow. I fertilised it last Sunday with one for acid loving plants then used Seasol two days ago.

I water regularly when the soil is drying out and the tree has a lot of new growth so it seems healthy. The soil ph is around 5.5 when I did the ph test.

I’m not sure if it’s a sign of nutrient deficiency, I put Seasol too soon or it’s something else.

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Abigail

Another leaf from the same potted magnolia.

We have a south facing balcony that has bright indirect light.

I found a pest on the other magnolia plant but I don’t think it’s what’s causing the yellowing of the leaves.

Would appreciate some advice.

Thanks!

JacobZ

https://www.workshop.bunnings.com.au/discussion/comment/58295#Comment_58295

Hi @Abigail,

Welcome to the Bunnings Workshop community, it is fantastic to have you with us.

Magnolias, especially when grown in pots, will occasionally shed older leaves as part of their natural cycle, particularly during seasonal changes or after feeding. The yellowing you’re seeing on your magnolia leaves looks quite typical of mild nutrient stress or natural leaf ageing. The yellowing between the veins, while newer growth remains green, suggests it’s not a major deficiency. Since your plant has plenty of healthy new growth, I wouldn't be too concerned.

The fertiliser for acid-loving plants you used is suitable, and applying Seasol two days later shouldn't have caused any harm. However, it’s best to space fertiliser and tonic applications by about two weeks in future to give the roots time to absorb nutrients without overlap.

The insect in your photo looks like a small fly, likely a fungus gnat or a harmless visitor rather than a pest that damages leaves. These insects are often attracted to damp potting mix rather than the plant itself. If you notice a few hovering around the soil, let the top couple of centimetres dry out between waterings, as that discourages them from breeding.

The dark, round patch on the leaf appears to be a minor fungal or bacterial spot rather than pest activity. It’s quite common on magnolias, especially when moisture sits on the leaves or after physical damage. You can safely remove any affected leaves to prevent spread and improve the plant’s appearance. Ensuring good airflow around the foliage will also help.

Overall, your magnolia looks healthy and well cared for. Remove the yellow or spotted leaves, continue watering consistently but avoid overwatering, and hold off on fertilising again for a couple of weeks. Keep an eye on new growth, as long as it remains green and strong; the plant is thriving. This minor yellowing is normal and should resolve as the plant continues its seasonal growth.

Keep us updated. If anything changes and you are concerned, don't hesitate to reach out.

Jacob

Abigail

https://www.workshop.bunnings.com.au/discussion/comment/91503#Comment_91503

Hi @JacobZ ,

Thank you for all the feedback, I appreciate it.

I will take on what you mentioned and look out for any other leaves that might have similar symptoms.

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