I am having the very same issue with my dwarf meyer lemon. It is potted and in the house and it's leaves looked very healthy throughout the winter, the little green lemons have been turning black since I've gotten it though. I bought it about 2 years old and it stands about 2 feet high. Now the leaves have fallen off two of the larger branches of the tree. I water mine about 2xs a week.

In most cases, overwatering causes fruit to blacken.
Nix, how often does your neighbor water her/his citrus? You say your tree gets about 6 hours of sun..is it full, direct sun or bright?
Does soil drain well while you have the hose running? If water builds up w/o proper drainage, overwatering may be the problem.

Cyndi..what size pot is your citrus in? What type of soil is your plant in? Like Nix, since you're watering twice a week, overwatering could be the problem. Allow soil to dry between. Inspect soil with your finger or probe. Insert deeply. If you use a finger, and it comes out wet/moist, wait a few days before adding more water. Good luck to you both. Reduce watering, use well-draining soils, and see how your citrus do..Toni

Help,
My Meyer Lemon tree is making fruit but when small grape size they are turning black. I mist several times a day to keep them humidified and I foliar feed daily with mild solution of Peters 25-5-15. What am I doing wrong. I need help, I don't want to loose this tree.
Emmett
Tree is in pots, indoors and getting 4-5 hours sunlight and leaves are dark green.

I know you mean well, but unless you have a fan moving air about your tree, stop misting to avoid disease on your leaves and fruit..

Why not use a humidfyer although you don't need humidity to have healthy trees)

Also, turn to feeding through the roots more so that the leaves..You might notice a difference and if not, it could be any number of other issues..

Pics would help)

MIke

To all those that replied, Thank you for your help. I foliar feed with a very,very mild solution because the plant roots don't dry out and often it's two weeks so then I feed and water them through the roots but leaves were fading and budding all but stopped so as I do with many of my potted plants, I foliar feed with very mild(1/4 to 1/8 th solution which feeds and humidifies. No I don't have a humidifier but Millet from another site and grows hundreds of container lemon trees stated that citrus love misting and or humidity so I mist them.

I will cease this or at least down to once a day with just rain water and watch. Another person stated that poor pollination may have cause this so now I pollinate manually with a very fine cosmetic brush and move the pollen onto the receptor or stamen and as new buds open I will continue since almost all the bees have gone away. My clementine tree which gets the same misting and feeding has gone crazy with fuiting and the leaves are as green as can be with no rot of mildew but I am no expert so I will watch what I'm doing, backing off as recommended and I'll let you know how things change.
Thanks again to all that replied.
Sincerely,
marcom13
Emmett

I live in Sun City, CA 92586 zip code which I believe is zone 9A (?). I moved in early last July and am trying to rehab a LONG neglected yard. There is a Meyer Lemon, planted in ground, that is about 20-25 years old or so. When I moved in, it was LOADED with lemons (still green/growing) and eventually kept me, several neighbors, my family well supplied (and then some!!!). In mid-February, I had a gardener trim/clean out the center of the tree, and some "dead wood" from the top and perimeter to open it up a bit. Now it's the end of May, and a have a lot of set fruit, largest is probably silver dollar size, smallest just set and growing, and still lots of flowers and new buds coming. Tree looks super happy, but some of the small set fruit is turning yellow then black dry and shrivled. In many cases, large set fruit, small, flowers, new buds and a couple yellow or black baby fruit are on the same branch. This has been going on for a month or so and it doesn't seem to be impacting the rest of the fruit production or tree growth. Since I didn't live here this time last year I don't know if maybe it's normal...self selection maybe? Any clue what may be causing some new fruit to yellow/blacken?

Normal behavior. The tree is aborting some of the fruit it cannot handle. Not every blossom can grow into a lemon. It's just too much for the tree. I think this is considered the June fruit drop because we are almost there. My trees have been doing this too. You may want to fertilize the tree because it takes a lot of energy to bear fruit.

I never had a problem for 15 years. Now the tiny buds of lemon have turned black. This is the first year that I bought the fertilizer spikes for citrus. I think it is too strong, I diluted them in a big can but I won’t use them again. I have no fungus at all.

John, tell us how you really feel... lol