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How to treat magnolia leaves turning yellow?

Hi all,

Trying to work out why our little gem magnolia is turning yellow with brown spots.
Located in prospect SA, and have been in this position for >12 months.

they get watered every 2 weeks but it’s been winter and raining frequently. fertilised every 6 weeks with seasol
they are still flowering but the leaves look unhappy!

Any help would be appreciated!

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Comments

MitchellMc

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

It sounds like your Little Gem magnolia is experiencing some stress, which could be due to a few factors, especially as we're moving from spring into summer and water needs have increased. Although watering every two weeks may have been sufficient during winter when rain was frequent and temperatures were cooler, the warmer weather of spring and the upcoming summer may require more frequent watering. Magnolias like consistent moisture, and with the shift in seasons, they might not be getting enough.

A good practice is to check the moisture level of the soil between watering to ensure it’s still damp enough for the roots. You can do this by sticking your finger into the soil to feel for moisture or using a moisture meter. If the soil feels dry, it’s a sign that you may need to increase your watering frequency. Magnolia roots spread out shallowly, so they can dry out quickly in warmer weather.

The yellowing leaves with brown spots could also indicate nutrient deficiencies or potential fungal issues. While applying Seasol is good, it's not a fertiliser; it is only a health tonic and lacks the necessary nutrients for healthy plant growth. It would be worth switching to a balanced slow-release fertiliser designed for flowering plants. Magnolias benefit from fertilizers rich in nitrogen, phosphorus, and potassium to support healthy growth and flowering. Keep an eye on the drainage, too, as soggy soil can lead to root issues, especially if there’s been a lot of rain recently. Ensuring proper drainage will help avoid waterlogged roots, which can also cause yellowing leaves.

Please let me know if you have any questions.

Mitchell

Blyth

help! My evergreen magnolias are yellow and straggly - I’ve fed with seasol and also an azalea fertiliser. Soil ph testing I wasn’t sure about but seems to be about 7 / neutral. We are in Melbourne and they are by a pool. Any suggestions welcome please!

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/57980#Comment_57980

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

It looks like your magnolia is showing signs of nutrient deficiency. The yellowing leaves with green veins suggest an iron or magnesium deficiency, often caused by soil that’s slightly too neutral or alkaline for magnolias, which prefer a mildly acidic pH of around 5.5 to 6.5.

Since you mentioned feeding with Seasol and an azalea fertiliser, can I ask when you last applied the fertiliser? It’s important not to double-dose, as too much can stress the roots further. For now, make sure the soil stays evenly moist with deep watering once or twice a week is best, and continue using an acid-loving fertiliser only as per the label directions. You can also supplement with a trace elements mix to help correct the deficiency. Keep in mind that it will take some time for the plant to recover, and the yellow leaves won’t turn green again. You’ll need to wait for new, healthy green leaves to appear as the magnolia responds to the improved conditions.

Please let me know if you have any questions.

Mitchell

Blyth

https://www.workshop.bunnings.com.au/discussion/comment/91336#Comment_91336

Thanks so much Mitchell

i put seasol on about a month ago and the azalea fertiliser on three weeks ago. I probably haven’t been watering more than once a week so I can up that for a bit. Is there anything I can do to lower the pH a bit more or will the azalea fertiliser be adequate?

EricL

https://www.workshop.bunnings.com.au/discussion/comment/111642#Comment_111642

Hello @Blyth

Since you’re already using an azalea fertiliser, that’s an acid-forming type specifically designed to gently lower soil pH over time. In most cases, that fertiliser alone is adequate for maintaining the slightly acidic conditions magnolias prefer, especially if you use it regularly and water it in well. Increasing your watering to twice a week for the next few weeks will help the nutrients move through the root zone and make the soil chemistry more stable.

If you suspect your soil is still too alkaline despite that, you can give it a small boost by incorporating organic material that supports acidity, such as pine bark mulch, peat moss, or composted oak leaves. These natural amendments lower pH gradually and safely. Avoid adding elemental sulfur or aluminum sulfate unless a soil test shows the pH is well above 7.0, as those can make the soil too acidic or damage roots if misapplied.

If you need further assistance, please let us know.

Eric

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