It is one of 3 things.

1. under watering

2. Root damage

3. water channeling

Pull the tree from the container and examine the roots.

I second Silica

Mike

Thanks, guys. I guess I was approaching it from the wrong perspective. I had already pulled the tree out of the container and the roots look ok and not root bound. I aloo made sure the container had good drainage. I'll give it a good soaking.

You don't have to worry about soaking the tree. I have many times soaked container citrus trees over night.. Citrus roots do not begin to show damage when in floods until two days of being submerged.

Awesome! Thanks for the advice. I was afraid of overwatering. These citrus I have were end of season derelicts left on the clearance isle that I have nursed back to health and didn't want to damage them.

my lisbon does the same thing. None of my other citrus do this, so I just wonder if theyre not very heat tolerant.

Same foe me. I gave the Lisbon a good soak last night and it does seem the leaves are a bit perkier this morning. I don't suppose there's been enough time for them to be normal. And you may be right, it could be heat related. This Lisbon was in the sun for probably 3 hours, but it was direct afternoon sun. The container would get pretty warm and I would think if nothing else it would accelerate the soil drying out. The others get morning sun with part shade in the afternoon.

Citrus can take (and need!) a LOT of water when actively growing in the warm summer season. For mine, it's when it's cooler and they slow down that watering becomes more critical. Your tree has a lot of leaves and will be transpiring quickly. Water that well.

Hi Tony. In 1955 C.P North and A.Wallace published a study titled Soil Temperature and Citrus in California Agriculture. They used 5 year old Valencia Orange on sweet root stock planted in wooden boxes with glass sides and carefully controlled soil temperature to observe the root elongation. They found maximum root elongation at 80-90F. Considerable elongation was noted at 100F. Roots died at 105F. Yes you have different rootstock but another study with 4 different rootstocks found similar results. Here are some samples I took the other day when air temperature was 90F. I live in Toronto Canada. You have to move the pot to the shade for a few days. These infrared thermometers are worth $20 on Amazon. You can use it to determine when to water your lawn as well. Nurseries don't grow in full sun, they grow under shade cloth. I use a patio umbrella. When the pot gets over 100F it is 🌮 taco time for the leaves. When you place a container on concrete, ashphalt or wood the pot will pick up heat. Concrete, wood and ashphalt are like ovens. Beautiful tree by the way. I am sure it will be fine in a couple days of shade. Keep in mind your beautiful tree also doesn't have the root to shoot ratio it would in the ground so don't over stress it in the heat. I prefer to use clay pots because they naturally cool down like a wineskin when moisture evaporates from the clay.

The dark black pot isn't helping

I agree with that

Dave, thanks for the advice. That makes total sense. I will certainly keep that in mind and adjust my watering appropriately. I think I've been a little too cautious about overwatering.

Lemon Lime Orange Zone 6a, that's an interesting read. Valuable information to take to heart. I do have an infrared thermometer (actually use it for the grill). I'll put it to another good use. I never thought of using it to read container temps. Its sometimes easy to forget that container grown trees (plants in general) don't have the advantage of stable root temperatures as they would if planted in the ground.

Thanks all for the great advice. The tree is already perking up and looking much happier. it has a ways to go yet, but it's on the right path. Thanks again.

Edit -- Lemon Lime Orage Zone 6a, forgot to mention the tree is in a much cooler, shadier spot. Also, I didn't realize Toronto got that warm in the summer. That's almost Texas heat. :-)

Hi Tony. Love the Great State of Texas. Beautiful State. Great people. Another cool use for your infrared thermometer is measuring the lawn. There is a large Delta between green grass that is healthy and grass that has dried out. Helps adjust the irrigation.