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In the images of my citrus below, you can see the leaves are paling towards the edges. What is the deficiency and how can I fix it? The soil is clay-dominated with some sand and coloured red, geologically ancient (Adelaide Plains, South Australia), and was probably under seawater or a marine swamp 1000+ years ago, so not very rich in organic material.

I'm not sure if it's a lime or lemon tree since I haven't seen the mature fruit yet.

leaf paling towards edges

closeup - leaves paling towards edges

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up vote 9 down vote accepted

Although I haven't come across this problem myself, I have done some research and would say, judging from the first (smaller) photo, that this is probably a magnesium deficiency, to which citrus trees are fairly prone:

Mg -- Always on the oldest leaves first. Bottom center of the leaf is green, and the end and sides are yellow or orange, making an inverted "v" or "Christmas tree" shape to the green part, as it zigzags with the veins.

Magnesium deficiency produces a very distinct yellowing towards the apex of the older leaves, with a triangular area remaining green at the leaf base. Affected leaves fall prematurely in late summer and autumn. The defoliation can be heavy when a large crop is being carried. If the deficiency is not corrected it weakens trees.

Magnesium deficiency in citrus

Apparently, it can be treated with a solution of Epsom Salt (magnesium sulphate, 2 teaspoons dissolved in a litre of water) applied round the base of the tree or, for a quicker result, as a foliar spray:

Magnesium Deficient Plants

There is some useful information about magnesium and Epsom Salt here

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HUGE generalisation, but many red soils do lack minerals such as magnesium If there are other problems with other plants, it might be worth having a soil analysis done. –  winwaed Jul 5 '11 at 12:49
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The lime tree is doing much better now. I poured dissolved epsom salts all over the leaves and added it in undissolved form to the soil. Now it's spring I've also fertilised with Dynamic lifter (organic multi-nutrient) so in case it's not Mg deficient I have all bases covered! –  Lisa Sep 16 '11 at 2:53

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