Who woulda thought... a meyer lemon, causing trouble.

So about 4 months ago I received my first meyer lemon. I was hesitant to spend any amount of money on it, with the meyer's reputation of being problematic but I loved the fruit. So I just ordered a small 10 inch cutting. I barerooted it, cleaned off all the old soil and replanted in a pine/perlite/peat mix. Not a single discolored nor dropped leaf for the 3 weeks I had it. Unfortunately, at some point one afternoon my dog pulled the entire plant straight out of its pot and it layed in our hot driveway for the entire day and died.

So 2 months ago, fresh with my success with the smaller meyer, I ordered a larger tree my dog wouldn't bother. It arrived in horrible condition. Lots of yellow leaves, a scale infestation, appeared to be in straight dirt. I tried to contact the seller, but no dice on getting any kind of communication. I decided to keep it anyway, so I carefully removed all the old soil and potted it in a pine/perlite/peat mix. I quarantined it inside because of the scale & scrubbed the entire tree with a tooth brush + soapy water. A week later I treated it with all season/dormant oil. Over the next 3 weeks it perked up and turned green and was looking good. I treated with dormant oil one last time and then a couple of days later stuck it outside in a shady spot. Within a couple of days leaves were turning yellow and falling off. I brought it back inside and the leaves stayed yellow and continued to be shed. I figured I might as well stick it back outside and it has been there ever since. It has stopped shedding leaves and is starting to put on a good amount of new growth, but the leaves keep turning yellow. No leaf drop in 2 weeks. Am I worrying about nothing or am I doing something wrong?

It has been raining heavy at least a couple times a week for the last month so I haven't needed to water. The soil looks dry but is wet less than half an inch down.

- I've fertilized twice a month with foliage pro. I just applied Dynamite slow release fert and plan to supplement that with a lower (1/2 strength) dose of foliage pro every 2 weeks until fall.

- It has been moved into full sun for a month now. About 13 hours a day.

- Last night I moved it into the sandy area, away from my other trees, to treat with dormant oil after finding some new scale.

I do not see any new growth, but that yellow leaf looks like an old leaf the tree is about to discard. The other leaves do look like they are not getting enough N, but since you have only had it for 2 months and have already fertilized it, you may just need to give it some time. You could add a water soluble fertilizer with each watering at 300 ppm N until you get it greened up.

Thanks, Skeeter. The new growth is only on the one branch. There are 4 or 5 new shoots coming out but I didn't try and get a pic of it. I'll see if the fertilizer helps out.

The actual reason why the old leaf has turned yellow, is because the tree has taken back (withdrawn) all of the usable nitrogen from the leaf, before it will discard it. As soon as a citrus leaf know longer "pulls it weight" and is using more energy than it provides the tree, it is quickly discarded. There is no welfare program for old citrus leaves. When the leaf was new, the tree provided the leaf with enough nitrogen for the leaf to grow and become dark green. Now that the leaf has spent it usable life, the tree is taking the nitrogen back, and will again distribute it where it can once again be beneficial to the tree. Nature does not waste anything. - Millet (911-)

When my trees are over-watered (both in-ground and in containers) the very first sign I see is some yellowing of one leaf (sometimes two) and the particular leaf is always either 1) low in the canopy or 2) very close to the trunk, usually both. This happens to me a lot when I'm learning how often to water a recently planted in-ground tree or when I test a heavier media mix. I cut back watering right away and only will lose a couple more leaves total.

The yellowing (and eventual discard) of the leaf looks very similar to yours.

It could very well be the natural aging process of leaves, as Millet has described. But what caught my attention from your post was the heavy rains, new mix, and the look and location of the leaf.

Something to keep in mind if it continues.