I have a dozen citrus trees, most of which are very green and healthy. Three, however, are very yellow (lemon, key lime, grapefruit). The key lime and lemon lost a lot of leaves over the winter and were generally unhealthy despite my best efforts so I am less shocked by their issues. The grapefruit, however, used to be dark green with big healthy leaves. The grapefruit didn't sprout any growth whatsoever in the first year, basically did nothing over the winter (no leaf drop) and when I repotted all trees this spring it had by far the biggest, healthiest root system with tons of white root tips all over. All dozen trees sprouted new growth when brought outside in spring. Some new leaves were purple, green, or yellow depending on the tree when brand new, and then greened up rapidly to a dark green. On the three trees I mentioned, the new leaves started yellow and stayed yellow. Their old leaves also yellowed and started falling off, but they appear to just be old as other trees have shed their old leaves, which slowly rippled and turned yellow before dropping off.

The thing that worries me is that none of the three mentioned have greened up. They are very yellow with only a slight green tinge. There does not seem to be veined coloring like shown in some of the nutrient deficiency pictures, they are just pretty much lacking color all over.

All dozen trees have received identical care and are all in the same place outside. They have been fertilized, somewhat irregularly because I'm still figuring that out, but the fact that 9 out of 12 are dark green makes me suspect this isn't the issue.

My only guess is overwatering, or "that's just how they are, wait and see". I only water during droughts, but due to frequent rainfall they may be too damp. I am just astonished that the grapefruit isn't growing like wildfire based on the root system.

Potting mix is hardwood mulch, sand, perlite, and generic potting soil. I just eyeballed it, but I think it is heavy on mulch and perlite, lite on sand and potting soil. The soil does have some peat moss but the total peat content cannot be high at all based on the quantity of other ingredients. And again, all the other trees seem to be doing very well.

I will post pictures when I can find my memory card reader...

Hardwood bark can have high levels of manganese and that can cause some toxicity.

Brian, I do not know about the grapefruit, since I do not have one, but I do have a grafted lemon and a couple of seedling key limes. I have found that, with "all things being equal", my lemon seems to need more nutrition to maintain its deep green leaves than any of my other citrus. The new flush will be more yellow green than light green, and if not fertilized quickly, will stay a pale yellow green color. I don't know if it has to do with its rootstock (unknown) or if it is a lemon issue. I fertilize with MG 24-8-16 with micros, and twice in the summer add a little extra micros, especially when I see this yellowing on my lemon leaves. I fertilize every watering, to a 5 gallon bucket I add 2 teaspoons MG, 0.5 teaspoon Epson salt. I also have a slow release in the soil.

All that being said, with all the rain we have had lately, it would be easy to overwater and/or underfeed your trees. I have a well draining mix, so overwatering is not much of an issue, but underfeeding I have to be careful with as it is easy to skip watering when mother nature has been doing it so frequently. Since much of my tree's nutrition comes from it's routine watering by me, when it rains I can easily fall behind in their nutritional needs.

I think that there is not one formula for every tree, because it is based on the individual health of the tree, the rootstock characteristics and the growing conditions. There is a good place to start for all trees, though, and this is a great place to find that information. I only offer my observations because I have seen similar discrepancies in my trees when "all things are equal", however, I am certainly not an expert on these trees. I hope you find your answer. Barbara

I'm going to triple the amount of fertilizer given to all trees based on another post which suggest I am not using enough. I just started using slow-release granules so there should not be issues with it washing away.