Question
Dear C L Fornari,

Just to introduce myself, I am Cecilia from Bombay, India.

I would like your advice on growing marigold flowers.

I had a plant (a species of small marigold flowers) which I purchased and replanted it in a clay pot.  The plant was doing very well in a suuny spot in my balcony for about a month.
Then, all of sudden part of the foliage started turning yellow and drying out.  The flowers and buds were wilting in the sun and recovering after watering it the second time in the day but the leaves continued turning yellow and drying out very quickly.

Within a few days, the whole plant totally dried out.

I don't know whether it was some root disease which killed the plant or water-logging.  Please advice so that the next time I am successful in growing marigolds.

Thanks,

Cecilia  

Answer
Cecilia,
I love marigolds, and I know that they are also appreciated in India.
It is unlikely that a root disease killed the plant, but the symptoms you describe DO have to do with the roots.  Yellowing foliage that turns brown can be the result of soil kept too wet or too dry.  Both cause the roots to die, which causes the foliage to first turn yellow and then brown.

Marigolds have a fairly deep root system, so be sure to plant them in a pot that is at least 12" across.  Water them very well (soak the soil) and then don't water again until the surface of the soil looks very dry (but before the plant wilts)  - when the surface looks dry, and it feels dry if you stick your finger in the dirt, then water deeply again.  

I hope this helps... let me know if you have any follow-up questions!
C.L.