Hi, I recently planted some citrus along my northern boundary of my house. I planted this young lemon tree in sandy loam that had some cow and chicken manure and a little bit of mushroom compost mixed through. It sits in almost full sun except in the late afternoon.

When I purchased the tree it had slight yellowing of the top leaves, which I thought might be new growth (?)
I gave it a good soak when first planted 2.5 weeks ago and then it rained here in Adelaide for the next week. I had put 'forest mulch' on top and was told that this might of caused the yellowing of the leaves. I was told to put citrus fertiliser on to remedy what could be a nitrogen deficiency which I also watered in.

My initial thoughts were that I have over watered as an adjacent newly planted lime tree had started to drop leaves. So I haven't watered the garden bed for 1.5 weeks but after a day of 35°C heat yesterday my lemon tree is looking unwell. Is this a sign it needs a water or is there something else going on???