Why do the leaves on my Meyer lemon have blotchy yellow areas?

Question

I have a Meyer lemon that I purchased a few months ago. I potted it into a self watering container with some potting mix mixed with some peat. It's flowering and small fruit are forming but the leaves are not looking wonderfully healthy. There are yellow splotches on the new leaves, and on the old.

The temperature is in the very low 20s Celsius (60s Fahrenheit), and I've only given it some citrus fertiliser only once when I got it.

My pH meter, which I've never used before, is saying pH is about 7.6, moisture level 2/10, but when placed into water it only reads 6/10 so the whole thing may be junk. So this should be low enough to absorb manganese though looks like iron might be a marginal.

Should I try acidifying the soil with some sulfur or do something else?

pH reading

young leaves

older leaf

whole tree

I had a similar device that had the same problem with the moisture level. — Alina, Dec 27 '16 at 06:59
Check for spider mites under the leaves, that may be part of the problem — kevinskio, Dec 27 '16 at 20:47
I used a neem spray a couple of weeks ago for aphids, but I don't see any evidence of spider mites now — Graham Chiu, Dec 27 '16 at 21:24
Are those little white things near the central vein of the leaf whitefly debris? If so, there you go. In general, I associate this kind of blotchiness with a bug problem - but I'm no expert! Another critter you should be looking for is garden scale. — Ed Staub, Feb 15 '17 at 06:13
@EdStaub There's no signs of whitefly nor scale insects. The new leaves don't show any problems so I'm assuming it was a transient nutrient issue. — Graham Chiu, Feb 15 '17 at 06:56

score 1 · Answer 1 · edited Apr 15 '17 at 19:23

This looks like a nutritional imbalance. Unless you like to play the chemist lottery, the best fertilizer would be the complete type, including a 3:1:2 NPK but also including calcium, magnesium, sulphur and all the micro nutrients. Some of the plant specific fertilizers are all marketing and missing important ingredients.

Stick your finger deep into the soil and see that the potting mix does not become hydrophobic. I assume it drains well.

Why do the leaves on my Meyer lemon have blotchy yellow areas?

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