Citrus are heavy feeders, are you feeding regularly with a micronutrient fertilizer? Realistically it's almost impossible to tell what nutrient is missing from the plant, and it's not relevant because the solution is always the same, give it a good fertilizer with all the micro nutrients. Don't bother with the epsom salts or iron, just go for a nice slow release fert with all the micros. I like osmocote plus which is 15-9-12 and has all the micronutrients. In the mean time you can give it some dyna-gro liquid foliar-pro at a low dose if you have it lying around. The osmocote plus can be had at home depot for about 20$ or so, it's not cheap, but it's good stuff. Here's my reasoning, you're not going to alter the pH of your soil easily with a plant in the ground, and you're still going to need to add fertilizer.

Phosphorous is locked up by the pH. It's in the soil but until you drop the pH a bit, it shows as lacking. That's why they fertilize with it....so the plant will find it readily available. If you set up an environment that the soil microbes can really get going in, then the phosphorous will be unlocked. If I add anything when I plant a potted item, it's some Rocket Fuel by Gardenville. Just a teaspoon so the plant has some help until the soil relationships are set up. Too much and it could actually slow down the microbes. Organic matter is the big key to our soils. We have so little of it that it sticks together. Every time you have plant debris leave you area, you've lost the nutrients that the plant used in those leaves and branches. If you don't put that back (and a little more for next years growth), you deplete the soil. But fertilizer alone won't fix the problem. You have to return the organic matter of the leaves and branches too.......hence compost should be added. Working the land properly is much more difficult than plowing, fertilizing and spraying pests. It requires close monitoring of the soil and rotating animals and plants around to keep everything at it's peak. Even weeds have their place in this dance as do insects. Chemicals won't fix the problem completely but sweat and smarts will.

I made thus post six years ago, though it says five for some reason, and people have responded recently? I only found this post because I was researching revisiting the idea of trying zucchini plants. What do you only want to plant organic, is that what's with the milk? Umm, I didn't say I used milk as fertilizer, in fact I used miracle gro. I said I added milk to soil to supplement. Jeez. Reading this, I see why I stopped using kk but houzze, People here are nasty. Not everyone but a lot.Oh I wonder if that posters related to the idiot growing tomato's on her father's lawn, well maybe not in So many words but that's basically what thay Donna lady said. Oy!ading this, I see why I stopped using houzze, People here are nasty. Not everyone but a lot.Oh I wonder if that posters related to the idiot growing tomato's on her father's lawn, well maybe not in So many words but that's basically what thay Donna lady said. Oy! What do you only want to plant organic, is that what's with the milk? Ummm, I didn't say I used milk as fertilizer, in fact I used miracle gro. I said I added milk to soil yo supplement. Jeez. ..u can't use compost in a container. Ummm actually what to you.thinkba compost bin us? Fight s container. Iv composted for years with good results but Iv always supplemented with miracle gro with good results. ... I get it, milk as I saw first hand won't cure blossom end rot, but it was a last resort in the middle of NY garden season. You live you learn. B to the way, if u read my post, I was mostly asking if the milk could do o harm. I did get some helpful advice though. I don't know why everyone kept saying on here the plant was suffering from poor watering when I kept saying plant was moist. And I,f I was putting in the time make all those amendments, why wouldn't I have taken the time to water? Really. Maybe zucchini in is just hard to grow in containers, who knows. .... I get it, milk as I saw first hand won't cure blossom end rot, but it was a last resort in the middle of NY garden season. I don't know why everyone kept saying on here the plant was suffering from poor watering when I kept saying plant was moist. And I,f I was putting in the time make all those amendments, why wouldn't I have taken the time to water? Really. Maybe zucchini in is just hard to grow in containers, who knows. it, milk as I saw first hand won't cure blossom end rot, but it was a last resort in the middle of NY garden season. I don't know why everyone kept saying on here the plant was suffering from poor watering when I kept saying plant was moist. And I,f I was putting in the time make all those amendments, why wouldn't I have taken the time to water? Really. Maybe zucchini in is just hard to grow in containers, who knows.

Using chlorosis patterns in leaves to determine a nutrition deficiency is a bit of a crap shoot because there are many overlapping/vague chlorosis patterns. You really should take a soil sample & submit to a reputable lab for analysis. Applying too much of one nutrient can mess up the availability of other nutrients to your plant. So again my advice is, do a good quality soil test before adding a bunch of nutrients, especially the secondary & micro nutrients.