Here's a photo of the leaves.

Here is a link that might be useful: {{gwi:397696}}

Lemon trees are the largest of the citrus (unless you have a dwarf) and usually produce a bountiful crop. Your photo is great. Yellowing of new leaves generally means the tree isn't pulling enough iron from the soil. Yellowing of older leaves can be an indication that your tree isn't able to absorb enough nitrogen from the soil. When soils are cool it is harder for plants to process the nutrients. The same is true for soils that are too moist - the roots need oxygen in order to use the nutrients.

As long as you are watering correctly I wouldn't be too concerned about your tree. The new leaves on your tree look ok and you have blossoms. Experts don't recommend fertilizing trees that have been in the ground less than one year. I bet as the soil temperatures begin to warm your tree will take on a darker green appearance. The leaves that already show chlorosis (yellowing between the veins) will not improve, but the new growth should be fine.

Here's a link to information on watering and fertilizing citrus.

Here is a link that might be useful: Citrus care plus fertilizing and watering

Thanks! No, it's not a dwarf -- it was in a 24-inch box and is already ~8" tall. Before I got your message, I figured the problem was iron absorption caused by the "soil" here. So I went out and bought Hi-Yield Iron Plus (11-0-0) to acidify the soil and give it iron. I don't know how old the tree is, but I hope I haven't hurt it by adding the iron. Can't do anything about it now, so I'll wait and see.

Thanks again!

Great link - thanks Cathy!