You likely have black citrus aphids, perhaps a fungal infection, likely wet roots; and, if that is a terracotta pot evaporation means cool soil. I would take it out of the ground now to allow better drainage; then treat the whole plant with a good horticultural oil, maybe with a little copper. If your pot IS terracotta, I would recommend you change it to ceramic, plastic, or composite/resin; and at that time you will be able to inspect the roots for damage. Under high humidity conditions, aborted fruits will often turn black.

Hi John, it’s in a plastic pot right now. Will lift the whole thing out of the ground.

Would a fungal infection disappear over time- if the roots were wet and it can now drain easier?

I can not see any bugs anywhere on the tree, the fruit just seems to go black and die or vice versa.

Pot it out is the number 1 thing for me to do then. Should I still feed it a little during winter- it will be indoors, I’d like to prune it too.

Cheers

I suspect the problem is with the roots not functioning properly because they are in a poorly draining soil mix and because of the cold. I suggest you repot into a better draining mix such as the 5-1-1 or gritty mix.

I would not prune because it needs as much nutrients from photosynthesis as it can get.

Do not fertilize until it shows growth.

I don't think temperature is the problem but drainage. Fungus will not go away by itself. Needs to be treated. Get the tree out and wash all soil off. Cut every mushy and effected root off and then re pot in a well draining soil. you might want to do a search for All's 5-1-1 mix. Lots of information here. After re potting, keep in half shaded location and after couple of days give as much sun as you can get. Looks not like a very sunny spot right now?

Hi Susanne, when the sun comes up it gets sun all day there, photo was taken tonight at dusk. We had to put the pot in the ground to stop it being blown over when we first got the tree.

I’m in the uk and this 5-1-1 mix seems to be a US thing, I can get grit and mix with soil/compost or sand and repot after inspection.........?

Phillip another possibility to prevent the tree form blown over is to tie it to a garden post. I did that the first year with my citrus when I started. for the potting soil think Fast draining like for cactus. I'm sure you can get perlite where you are? Spagnum moos too. You could mix that into cactus potting mix.

L:ow temps encourage root rot.

I’ve found this sand below- good for cactus and such, drain well and mix with a bit of soil to? I’ll be moving the tree inside soon.

Lotsa smart folks in the RHS; I would tend to follow whatever they say.

I used to be a member of the RHS (Royal Horticultural Society). Actually the reason that I joined the society was so that I could attend the Chelsea Flower Show in London on the first day of the show. The first day of the flower show is reserved for RHS members only. Chelsea is one of the largest flower shows in the world.

I de-potted the lime tree today, top 2” looked moist not wet, and the lower part looked fairly dry to be honest.

Maybe the pot in the ground did not allow the water to flow and now it’s out it’s ok?

photos were when taking soil out and then out of the pot. Do the roots really grow that close to the surface- 1” below

Looks pretty good. Yes, roots grow at or near the surface, which is why constant tilling for weeds is harmful to growth.

@johnmerr, so do you think the black dried out fruit and leaf drop could have been caused by the pot in the ground not being able to drain?

Caused by??? Difficult to say; but probably a contributing factor.