Welcome to GoY, Marsha!
Leaf loss in Japanese Aralias can be caused by a number of different things, so we need a little more information.
Are they in containers, or planted in the ground? Both lack of water and poor drainage can cause leaf loss, and that is easy to do in containers, though still possible with those in the ground.
What part of the country are they growing in? Southern Georgia, Florida, parts of the Gulf coast away from the ocean, the desert Southwest, and southwestern California away from the ocean all can get too hot for them in mid summer.
Sun exposure may also be a factor.
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welcome from me too.
Yes we will need more info and a photo if you can manage to upload one.