Q.Can U Help Me Identify Problem N Fix My Lemon Tree
My lemon tree was very healthy recently its not getting ny fruit with black stuff on stem n not very green leaves as in picture

Certified GKH Gardening Expert
That clay soil will be to blame.
This needs to be repotted into a mix of compost and potting soil, or a mix made for citrus. It will be a constant battle to keep them alive, until the trees are in the proper soil.
Here are some articles that will help:
https://www.gardeningknowhow.com/edible/fruits/lemons/how-to-grow-a-lemon-tree.htm
https://www.gardeningknowhow.com/edible/fruits/lemons/repotting-lemon-trees.htm
https://www.gardeningknowhow.com/edible/fruits/lemons/growing-lemon-trees-containers.htm