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How to revive gardenia?

I have a gardenia gifted to me 18 months ago that I am struggling to achieve consistent good health with. I have rotated between Kahoona and Osmocote for gardenias etc over appropriate intervals, I had good flowers but continually suffer poor leaf health on and off. I know the culprit is likely to be magnesium or iron, but do not know. Hoping someone with better knowledge than me can tell me what I should try. Thanks

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JacobZ

Hi @Ez,

Thank you for your question and welcome to the Bunnings Workshop community, it is fantastic to have you with us.

You look to have a couple of issues going on. The yellowing and dying leaves, as well as some pests eating your leaves.

I suspect that the yellowing leaves are due to a nutrient deficiency, likely magnesium or iron as you have said. As you have said you are applying fertilisers aimed at Gardenias at regular intervals, I suspect the issue is with the plant's ability to intake the nutrients which could be due to the PH of the soil.

High soil pH (alkaline soil) can block nutrient absorption in Gardenias, especially iron and magnesium, leading to yellowing and browning. I'd suggest grabbing a Manutec Garden Care Products Soil PH Test Kit and checking your soil. Gardenias like slightly acidic soil, somewhere between 5 - 6.5.

If you need to lower the PH, apply Manutec 1.5kg Sulphur Fine Granules following the instructions on the package to increase the acidity. If you need to increase the PH, use Richgro 5kg Natural Dolomite Lime to increase the alkalinity.

Along with the soil PH, you should be wary of how well-draining your soil is. Waterlogged soil can cause the roots to become oxygen-starved, leading to yellow leaves with brown, crispy tips. Ensure the top 2-3cm of soil below the mulch is dry before watering.

Mix in compost such as Osmocote 25L Scotts Compost Premium Soil Improver mixed with Ki-Carma 20kg Coarse Landscape Sand to improve drainage and soil structure. Use a small garden fork such as this Cyclone Stainless Steel Fork Hand Tool to loosen compacted soil, being careful not to damage roots. This will allow better water flow and prevent water from pooling around the roots.

In terms of pests, have you noticed any small insects on the leaves?

If you spot any, I'd be happy to recommend a remedy, but you would need to identify what we're dealing with before I could recommend something.

Allow me to tag @Noelle to see if she has any further recommendations.

Jacob

Noelle

Hi @Ez

As well as the excellent advice given by Jacob, I would also suggest pulling the mulch back from over the gardenia's root system.

In addition to possible magnesium and iron deficiencies, your soil may be experiencing some nitrogen draw-down effect, whereby the microbes that release nitrogen in the soil for plants to take up move from the soil into the mulch to increase the rate of decomposition of the mulch. This creates a short-term nitrogen deficiency in the soil which may result in the gardenia leaves yellowing.

https://www.workshop.bunnings.com.au/discussion/comment/43400#Comment_43400

Thanks @JacobZ

The soil drains perfectly, I think your comments regarding the plant's inability to take up nutrients sounds bang on. Thank you for your brilliant suggestions! I will try all of that and hopefully be posting a future photo of a much healthier gardenia. Snails may be the culprit on the pest front....will keep and eye out for others.

https://www.workshop.bunnings.com.au/discussion/comment/43404#Comment_43404

Thanks @Noelle I will give a wider clearance with the mulch as you've suggested. Thanks for the additional advice. 👍

https://www.workshop.bunnings.com.au/discussion/comment/43400#Comment_43400

Tested the soil @JacobZ ... PH3.5, so seems I need to get some dolomite lime. Thank you... hopefully on the road to recovery.

JacobZ

https://www.workshop.bunnings.com.au/discussion/comment/83845#Comment_83845

Hi @Ez,

Looks like we've found our solution. Glad to hear the culprit has been found and your gardenias are on the road to recovery.

Keep us in the loop. If you have any issues in the future, don't hesitate to reach out.

Jacob

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