Nellie wrote:
I am fairly new to these. I planted 19 of these plants and within one week,
I noticed some yellowing, wilting and finally collapsing. Upon pulling the
stem I noticed that the base of the leaves was mushy and slimy. At first I
thought I did not watered enough after planting (they were grown in 10″
containers and blooming) so I watered. All three plants that have the same
problem are on the same row. What do I do? The other plants seem OK so far.
Is it something in the soil? I am in Zone 10 (Miami, FL). They have
plenty of sun, southern exposure, some shade in the morning. What do I do
before they all die? Are the roots still alive? should I dig them out and
treat the soil? Please help!

Phil The Gardener’s Reply:
Agapanthus do very well year round in zones 7-11 and are generally disease
free as long as they have good drainage and are not over watered.

For your container plants, make sure you use a well drained potting mix, add
in a granular fertilizer. The soil should drain readily and not retain excess water.
The plant can suffer from root and rhizome rot in heavy poorly drained soil.

Remove the plant from the container and replace the soil with a good draining
potting soil replant. Check with your local garden supply for a good fungicide
to treat the affected plants and soil.

Happy Gardening

http://www.philthegardener.com/rotting-agapanthus/