Answer: Your question is a bit complicated to answer in that there are many factors which could be involved. Let me give it my best shot.
Your trees are most likely dealing with some root-related stresses. Citrus wants good drainage but fairly moist soil. In a container grown plant this can be difficult to achieve and maintain. Container size, especially in relation to citrus species and rootstock, can contribute to a plant prone to stress.
Small containers, growing media that is too "airy" (dries out too fast), and vigorous citrus species are likely to result in stress due to lack of moisture. Most citrus needs a very large container to stay happy and productive once they reach a mature, bearing age. A growing medium that tends to stay soggy, and trees growing in the cool, low light days of winter are likely to result in stress due to soggy, poorly aerated roots.
Citrus trees will drop fruit whenever stressed, especially when fruit is very still small. Lack of pollination will also result in fruit drop when the fruit is smaller than a "pea". The lack of green color in your lime leaves may be due to soggy conditions, now or in the recent past, which damaged roots. Loss of leaves in the greenhouse is most likely due to moisture stresses and/or the lower light levels of winter.
Hope this helps. Good luck with your citrus trees.
Q&A Library Searching Tips