After 20_+ years of growing various citrus trees, I have settled on Jack's Professional 25-5-15 water soluble fertilizer which also contains all of the needed trace minerals. Jack's supplies nutrition in the recommended 5-1-3 NPK ratio.

For inground and commercial type growing they talk about supplementing with micro sprays, and of course they are likely to do leaf testing to know for sure if it is needed. Just looking at your leaves is not the most accurate gauge of nutrient issues, of course. I just went ahead and got fertilome chelated iron, which has micros. Plus I use Jack's, largely on the recommendation of Silica :) I think kumquats may have greater zinc requirements than other citrus.

You might consider foliar feeding, which would help if it was a root/rootstock issue.

What about your soil mix (i.e. pH).

For container grown citrus you can't beat Jack's 25-5-15. The only downside to it is the smallest package you can get is 25 lbs.

Thanks all for the suggestion on Jacks, I had looked into it when I was first looking for a fertilizer, but I don't have storage for the larger bags and could only find it in larger quantities and only online, which is a bit too big for me to store. Hence, experimentation. Though I have tossed it into my book to try once I have a bit more space, and a few more trees. @hibiscus909 a test of the soil showed that it is only slightly more alkaline than neutral, (may have something to do with the insect treatments I had to use earlier this year), with only a slight alkalinity I don't know that it's too big of a problem, but I might try adding a tiny bit of vinegar to my water and see if that helps. I know that it is a zinc deficiency as the greenhouse where I bought the tree said they had been struggling with a zinc deficiency in their kumquats for awhile (went back and talked to them after it showed up again). In addition when it starts to show up, the newest growth comes in slightly stunted, a pretty good indication of a deficiency in zinc, which can be common in kumquats. (That's actually the reason I mention the Fukushu, as it hasn't had any of these problems and I use the same soil and fertilizer that I used on my Nagami). I can't do a foliar spray as the tree is indoors, does the fertilome work the same when applied to the roots?

Yes, soil application of zinc sulfate, zinc nitrate, or a fertilizer that contains zinc will also work to alleviate a zinc deficiency . Foliar spraying will work faster, but either will work.-

Yes, the Fertilome includes directions for both, and the spray does stain (iron!) so I do it outside. I only got one treatment done this spring, I wonder if its too late to treat again.

No still a lot of time

Depending on where you are, there should be plenty of time left. Thank you for the input, I'm going to try to see if I can find a small container of the fertilome and give it a try. I'm curious if this issue is typical of Nagami Kumquats, or if there is a way to avoid it by utilizing a different rootstock. Mostly curiosity, with a bit of personal interest for future trees.

So for an update, the nutrient deficiencies have disappeared after I watered with a bit of vinegar. (Thank you hibiscus for mentioning checking the PH, I had checked the PH on the soil I used in the original potting of this tree, noted that it was right and even a bit more on the acid side, and then didn't think to check my water. Turns out the water in my area has a lot of natural minerals making it somewhat alkaline, which was slowly adjusting soil PH. My other citrus don't seem to care, but evidently something about the Nagami makes it really sensitive to it. Something I'll have to pay attention to in the future). Leads me to investigate more alkaline tolerant rootstock combinations for the future. (I hope to do some grafting when I have a bit more room, but we plan to stay in the same general area so the water alkalinity will need to be considered). I'd be interested in other's experiences with this, I have perused a number of academic papers, but I find practical experience invaluable.

I had noticed that, both with my own experience, and from a lot of reading I did early on before I got my trees. In my area I found the fertilome at two separate garden supply stores, but both of them are a bit of a drive. It'll likely be necessary once my trees have exhausted their soil, but for now I simply need to watch my water PH. I found a pretty nice soil mix that contains composted bat guano which provides a lot of the necessary minerals that the trees need. At least the trees seem to like it. But I know that it won't last forever and eventually I'll need to provide more micros before I refresh the soil the next time I repot.

I really like Bio-live made by Down-To-Earth. It has everything and the kitchen sink thrown in.. including all the microbiology to break it all down and make it available. I top and/or side dress with that and also hit everything with fish emulsion from time to time. Heavy growth response and happy trees that would make Bob Ross proud!