United Kingdom 
Why are the leaves on my 6yr old magnolia tree not turning green? They are very yellow and have started to go brown on the tips. The tree flowered well this year (2nd year it has bloomed) but the leaves have now appeared but are staying yellow. A few of them are trying to gi green but not very successfully. I have fed it with rose and shrub food and a top dressing of ericaceous compost. I water it with rain water.
6 May, 2017
Answers
Is it in a pot? If so, how long's it been in the same pot?
6 May, 2017
Make sure your Magnolia has good drainage and doesn't sit in water or muck.
7 May, 2017
Many thanks to Moon Grower. I did as you suggested and gave it a feed of Maxicrop sequestered iron and the leaves are getting greener by the day. Thank you for your help.
29 May, 2017
Great!
29 May, 2017
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If you have alkaline soil your Magnolia is suffering from chlorosis needs a feed of sequestrene not rose and shrub food which will not help it at all. If you could add a photo to your question it would be useful.
6 May, 2017