Key Lime Tree - Leaves turning yellow and falling off. Twig die back.

[el3ments]

Hello, I'm having issues with my citrus trees. The key lime is having the worse time of the bunch. It looks like a nutritional deficiency.

I had issues using potting soil so I made my own potting mix which is similar to 5-1-1 mix. I was using all organic fertilizer but I'm giving up being all organic and starting to use Dyna-Grow Foilage-Pro. The trees have only received two mild doses of this fertilizer. I was hoping it would get rid of the issue I am having but so far I have the same issue.

I'm in Zone 5a. The plants have been inside since the very beginning of October. They started showing signs of a nutritional deficiency in late summer. I sprayed them with a citrus foliage spray and they seemed to do better but haven't grown much since. Since the plants have been inside I was giving them organic citrus fertilizer and using seaweed extract as a foliage spray and sometimes in the water the plants received.

My water is hard and the PH is at least 6.5 if not above 7. The organic fertilizer contains calcium so it's not helping. Would putting PH Down in my water, making it about a PH of 5.5 help lower the PH of my soil?

[Millet]

All in all the citrus in the last picture just looks under fertilized, as shown by the yellow/orange veins in the leaf center with some green out on the far sides (symptom for nitrogen deficiency).  The medium that the tree is growing in looks to be OK for adequate drainage and root zone oxygen availability.  Foliage Pro is a good  citrus  fertilizer, although expensive. Citrus are heavy feeders, therefore require more nutrition than most plants.   Organic fertilizers are OK, if there are ample microorganisms present to breakdown an organic fertilizer into a  form usable by the tree.  There is no where near enough microorganisms in container culture to accomplish this. Therefore, an organic fertilizer is not recommended in container culture.  The trees in the first picture shows that they are now growing in containers that are too small for the tree's size.   When a tree's root system  has  filled out all of the available container space, its growth becomes straight up, like toothpaste squeezed our of the tube.  Theses trees also show that they now have or have had an insect problem, probably mites.  They also need more nutrition. Welcome to the forum, happy to have you as a member. The best to you and your trees.

[el3ments]

Thank you for your reply Millet.

How do you know I have or had a mite problem? I'm trying to learn how to identify the signs. I ended up getting scale insects this summer unfortunately. May have even bought the trees that way. I bought them last Spring/Summer.

[lebmung]

I would prune the trees heavily if you plant to grow them in containers.
That organic fertilizer applied during the winter in your zone is a total killer. Bad bacteria and fungi in growing there because of low temperatures.
For limes yellow veins like you have is a good indication that roots are damaged. Limes are usually not grafted.