I suggest checking the soil moisture in the pot with a dowel. It is possible that the soil has dried out and is now hydrophobic.

If it is dry, then to re-wet, you may find it easiest to water them by placing in a 1.5-2" deep saucer and letting them suck up the water over 1/2 a day. I know some folks here are terrified of saucers, but for me, its the way to keep them hydrated when its 96F and 20% RH. In the summer months all of my potted citrus is sitting in saucers. All get a good dose of water every other day - AND - sit in a saucer until they suck up all the water. And they are perfectly healthy.

Oh, and once a week foliage pro or other high N food + vinegar does the trick. Note that i use vinegar at a bit less than 1 Tbsp per gallon (same rate as liquid food). Check your irrigation water pH - mine is 9.4 - hence vinegar is the ticket.

- good luck! - George

I used a chopstick to check the water last few days. It is hard for me to tell, the tip of the chopstick seems a little damp with a little dirt on it.

How do you check the water PH? I have a huge mature orange tree, I never water it, it seems ok.

I use a one-gallon plastic milk jar to water them. I probably pour in 1/4 of it per pot. Is it ok way to water the potted plant?

"little damp" does not sound like adequate moisture for summer heat. water by setting the pot in a saucer / bucket for an hour or two. and recheck with your stick.

pH can be measured by any pool/spa water kit. BTW: Make sure that you are not using water that has been softened by a sodium water softener (salt!).

I agree with Johnmerr, your trees certainly have the classic symptoms of being under fed. Citrus are heavy feeders requiring more nutrition than most plants. - Silica

Thank you so much to all! I am feeding fp 1tsb with 1 tsb vinegar per gallon water every watering and water more frequently (every 2-3 days). Hope they will recovery.