Q.Zinnia leaves drying
Bangalore, India. Zinnia plant lower leaves are turning brown and curling up. Stem is green above but seems to be drying up in lower part. Soil is moist and am watering regularly. One of the shoots went fully dry after flowering and I have trimmed it short. Grew this from seed – plant around 5 months old. Please help.

Zinnias are an annual flower and when done blooming the plants will began to brown and dry up.
You can dead head the flowers as they age to help promote 2nd flowering and more buds to form.
It does appear your plants are at the end of their life cycle.