Question
in a pot, what kind of care do they need. I water them nad
the leaves are dry and the flowers (red) are dying.

Answer
Natalie,
Zinnias are from Mexico, so what they like is sunny, hot and a bit on the dry side. What they hate is having their foliage splashed with water, being kept too wet, or growing in the shade. When the foliage is wet frequently, through watering or rain, they get leaf spot fungus and brown edges - the flowers also turn brown if they are splashed with water.

When in a pot, you want to let the soil dry between waterings but not to the point where the plants wilt. Water under the foliage, so that you don't get the leaves wet - fill the pot once and wait a few minutes and then water again to be sure that the root ball is throughly wet. Then wait until it is dry again before watering. Cut off any fading or dead flowers in order to stimulate new ones. And keep the pot in at least 6 hours if direct sun that includes the noon hour when the sun is strongest.

I hope this helps,
C.L.