A three year old, healthy Sweet Cecily plant has just wilted and died to the ground. When I dug it up - a smelly brown rot was on the roots. the location is full sun and the plants get watered three times weekly - deeply. Other plants in the same bed do not appear to have any problems. Any suggestions would be welcome - it has not been easy to find the plants at local nurseries and the client really liked the plant, so I would love to get some feedback.