I have two Meyers Lemons and a Key Lime in pots. They live outside in the warmer seasons and by the S window indoors otherwise. Had an unusual experience over the last month or so. All the trees were in bloom, with quite a few flowers. Now that the blooms are over, I noticed that the lime tree has set quite a few fruits (maybe 50% of the flowers), but both lemons did not set any (at lest as far as I can see).

All the trees were getting the same care (water, sun heat). In the years I've had these lemons, this is the first that they failed to set any fruit. All the trees appear to be healthy.

Any ideas as to what might have caused this lack of fruit set? The lemons (and lime) are forming/about to open new flower buds, so if there are some things to try I might still have time to do them.

Did at any time the Meyer lemons, while in bloom, ever become water stressed, or did you spray druing bloom? - Millet

Probably a yes to both. I did spray a insecticidal soap spray, because of aphids (which seems to be part of the winter blooming "ritual" here. I don't usually have issues with aphids at other times). And I will admit that I am not perfect in my watering schedule. So there were likely a time or two during bloom that the pots got drier than ideal before they got more water. But nothing extreme as far as I can tell. In fact in the last week, I noticed the lemons seem to require a bit more watering than the lime and have adjusted my schedule accordingly.

The odd thing (to me at least) was that I don't think this year was much different than past years. Certainly the spraying for aphids happened each year. And my precision with water schedules was probably equally loose. Yet there was a fruit set all prior years.

But what is this leading to Millet?

Trees that were not fertilized prior to the bloom period often drop excess number of blossoms, especially if soil fertility was extremely low. Improper irrigation is also responsible for blossom drop. Fruit trees in the blooming stage require very special attention in connection with soil moisture – they should never be allowed to stress for water – this will weaken the connecting layer of the flower to the stem. During the blooming period of a citrus tree, the water level in the tree's root zone should never become lower than 65% of field capacity. Any water stress at this time will result in little or no crop. - Millet

Well a bit of follow up on this. The trees are going through another flowering cycle. So I have tried to be more regular with my watering schedule. And I think I may have erred on the other side.

The flower bloom this time has been good, and while it is a bit soon to say, it appears that a better percentage of the flowers are starting to form fruit. However the bad thing which happened is some pretty drastic leaf loss. Maybe 50% or more of the leaves have dropped.

It is not dis-similar to what one might expect in the fall when first moving plants indoors and not taking care to match root temps and water needs of the above round parts. But I thought I had that under control. This fall went well with very minor if any leaf loss, and the trees were making it through the winter at a S facing window without any symptoms like this until I increased the watering schedule.

I had thought that I was letting the soil dry enough between watering, but I now suspect not. I was checking the soil moisture (index finger method) a inch or two down, and watering when dry. However I tried lifting the pots recently and noticed they were still quite heavy even when I thought the soil dry. Poking down further I found very moist soil a bit further down. My conclusion is I have been over watering, and that has caused the leaf drop. Does that make sense?

IIRC Millet had said elsewhere that one should wait until the pots feel light in weight before watering. I am curious if you still think this is a good technique (and perhaps wonder how dry/light you let them get? Really light/bone dry?)

Anyhow I am wondering what the best way to correct this over watering mistake (if that is what happened) is, in light of not wanting to ruin the fruit set which is hopefully taking place. Perhaps a slow move back to dryer soil conditions?

Suggestions?