My hostas have been in place for many years. Until recently, the ones with green leaves and white stripes were looking great and producing blooms. Then they began to experience a yellowing of the outer leaves. Now many of the leaves have yellow and surrounded by leaves that are a light brown. The summer has been relatively dry; a few inches down the soil often appears dry. Recently, we have been experiencing hot weather. When I have watered them, the leaves closest to the main body of the plant and the flower stems stand up looking straight and tall. What can I do to prevent this from happening? This also happened last year to the ones that have the out white stripe. The ones that no stripe appear to not have this problem but are in a different location and receive afternoon soon.
Yellowing leaves generally indicate watering issues. It does sound like they need more water.
I would trim up the plants and give them some water to help sustain them through the hot summer days.