not too sure, only thing i can think of is maybe fertilizer burn. have you fertilized recently? have you looked closely all over the tree to look for tiny pests?

Classic symptom of salt burn; most commonly from fertilizer. The color of the leaves indicates that your tree is VERY well fed, indeed.

What do you use and how often do you fertilize?

When was the last time you flushed your soil out with a good stream of fresh water until water runs out the bottom for at least a minute or so?

Do you water your mix in sips, or do you water until the water freely exits the bottom everytime?

What kind of mix do you use?

Is it in full or partial sun?

What kind of water do you use?

Mike

Thanks for the replies!

I normally use a dilute Miracle-gro liquid fertilizer (one where you feed like 5-10 drops every watering), but I have actually not fertilized these plants since I brought them outdoors about a month ago. During the winter I kept them indoors where I watered them with a good soak once a week, but since I brought them out I just let the rain do its job unless we are having an extended heat wave. They are in a typical bagged potting mix (not really sure what kind) and in pretty full sun. I use tap water.

I noticed that the soil around them was getting disturbed, is it possible that a neighbor's dog has been peeing on it?

Well, dog urine would do it; dog urine is very concentrated and can seriously burn young trees.

If it were my tree, I would lose the MG; it tends to build up in the soil and cause salt burns; besides it really isn't a very effective citrus fertilizer.

I gave it a good, long soak by letting a small stream of water from a hose flow and drain continuously through the pot for about an hour and moved it to a different area where hopefully the neighbor's dog won't get at it (assuming that is the problem). It's due to be repotted soon, too, so I guess I should get on that. I'm quite attached to this plant, it took months to start from seed...!