Help! Does my Meyer Lemon have salt burn and is my plan to fix it a good one?

Hi there! I’m desperately hoping someone can help me with my poor suffering Meyer lemon!

I’ve had this young tree for about 15 months, and periodically it sprouts a batch of brown spots out of nowhere. They all show up at once, a bunch of leaves are murdered and then the tree seems fine for a few more months. This has happened three or four times; it seems to appear a few weeks after each bloom and I thought maybe fertilizer could be a culprit but I’ve only fertilized 3 times and not always in sync with the bloom.

I’m in Zone 10a, in Oakland, California. It’s a very Mediterranean climate, rarely above 80 degrees and the coldest nights barely dip below 40. There are thriving mature Meyers all over my neighborhood.

My tree is on a southwest facing balcony, and gets plenty of sun and a regular breeze.

We’re under another balcony which provides rain shelter but means the tree is also not exposed to a ton of rainwater.

We have soft water here in Oakland but about six months ago I switched to distilled water in an attempt to correct this problem.  I’ve also tried copper fungicide (weekly for a couple of months per the advice of the website where I bought the tree) but that seems to have had no effect.

I water when the moisture meter is below 4 and give it at least a gallon of water, until water drains out the bottom but I fear I should actually be giving this plant many gallons and flushing the soil more at each watering.

I potted this in citrus/cactus soil and I drilled extra drain holes but I also think maybe the soil is staying too wet at the bottom (even though the top is bone dry.)

The first time this happened I thought maybe it was sun scald but it’s just not very hot out; the spots appeared this time after a long stretch of temps in the 60s, maybe a day or two in the 70s.

I THINK maybe this is salt damage, due to soil not draining enough/residual fertilizer/old tap water deposits. Do you think I am right about this?

My plan is to take out the tree, gently replace the soil, trim any rotten roots if I see them, and return it to this pot. I’m thinking of using a mix of vermiculite, organic catcus mix soil, and worm castings, then to continue fertilizing with worm castings instead of commercial fertilizer. Is this a good idea or could I be missing something? ‘

I’ve attached an image of the tree blooming about six weeks ago, and browning now (that probably started about a week ago). And I’ve attached some close-up images of the leaves. (I have a few leaf-miner marks but that seemed to be minimal, just a handful of leaves.)

I would be grateful for anyone’s advice on how to stop this browning from hurting my beloved tree! Thank you so much!!!

I think you are "root bound" Time to transplant to a larger pot with more fresh soil, before the roots start rotting...

In nature the roots would be equivalent to the size of the tree, so there's not enough root mass to feed it.

If you have reverse osmosis drinking water, you should give that a try, and if you get the right soil, you won't need any nutrients...

I agree with worm castings and possibly a few worms to keep the soil clean.  Larger pot to always have room for new roots to grow.
Is it possible bright sun on water droplets focused and burned parts of the leaves?

I agree that you need a bigger pot. I don't know if something with the roots is causing the spots but a healthier root system will help the plant fight off whatever it is. Too small of a pot is going to stress your tree. I'd try to get one that is at least 18" deep and twice as wide as what you have now

Other than the spots, your tree is looking pretty good and I bet it'll be happy with an upgrade.