Hi all, so I have a 7 foot lemon tree in a container in Switzerland.

1. It seems to have developed a few yellow leaves recently, I use citrus fertiliser with nearly every feed in the summer. Looking at the pics, do you think I am using too much or too little (of some nutrient) i.e. is it lacking something?

2. I have killed a number of citrus over the years, I am not proud of this I don't intent to kill this one as it's gorgeous!! I intend to bring the tree inside soon. I have a light and airy kitchen, and will sit the tree in a dish, with pebbles and water in the bottom (not touching the roots) to add to the humidity. However, I will try to keep the roots nice and warm, but I want to know how. The pot as you can see is quite big, would fairly lights really warm this potup? I can't really use a heat pad as there will be water in the bottom. Any suggestions?

PS - I know quite a few leaves have fallen off, this I think is due to the fact it faces east and has hot sun in the morning, when the roots are not warm enough yet. The new growth grows to about 3mm and then dies, which I also think is attributable to the roots.

Thanks for your help.

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I take strings of christmas lights (not LED) and wrap around my pots above the water tray. Last year this raised my soil temps up to around 78-80 degrees and stopped my winter leaf drop.

The deficiency is showing up only on the new leaves. So far the deficiency is not far enough along to clearly show exactly what the lacking mineral is. However, one leaf in particular seems to be fully deficient, and that leaf looks to be deficient in manganese in my opinion.

The symptoms for a manganese deficiency in citrus shows up on the very newest leaves, as having green veins WITH green border areas to the sides of the veins, on an otherwise yellow leaf. Leaves remain normal size with a manganese deficiency.

My Marisol Clementine gets some manganese deficiency most every spring. I correct it with a foliar spay and by soil application of a manganese supplement. If you happen to have some of Joe Real's AZ41 it works great as a foliar spray to control the deficiency. - Millet (851-)

ok, so Christmas lights or fairy lights it is then, i should be able to gaffa tape them to the pot to stop them going near the water. will leave them on over night, dont fancy leaving them on while im not in the house just in case of a fire etc

ok, will look this weekend for manganese spray/nutrients.

what do you think about my assumptions regarding the new growth dying? do you also think cold roots are to blame?

cheers

Could this be due to salt build up?

You mean the new growth dying or the yellowing leaves?

Both. My Meyer lemon had similar symptoms. I flushed the container and fertilized with Miracle-gro orchid food which also has trace elements and it seems to be slowly recovering. So I guess I had atleast one of the following problems:
1. Salt build up over summer from my slow release fertilizer
2. The pH got high
3. Some nutrient defeciency

So, it might be worthwhile to flush your container before you add the new fertilizer and bring it inside.