I am sorry for this delayed reply to your gardening question. The spring rush has brought a deluge of questions and we are working hard to catch up!
When the older leaves on an angel's trumpet turn yellow and drop it is usually a sign of drought stress. These plants tend to wilt and stress easily if they are in too much sun, especially late day sun, or if the soil is not kept moist. You may need to relocate the plants to a spot with less sun exposure but still good bright light. Mulching the soil surface and watering more often will also help. Finally if you haven't fertilized them recently consider providing a moderate application of fertilizer to provide some nitrogen which helps green up the plant.
Thanks for the question. Best wishes for a wonderful gardening season. Please stop in again soon!
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