Pansy issues

Hi

For the last few years my pansies have been very disappointing.

They are in a hanging basket, hanging under the edge of a pitched porch roof.

They are not enclosed and they receive run off rain water.

They are potted in potting compost of many makes, but the same thing happens,

They get greenfly in the dead of winter, they either grow tiny leaves with black spots or seem to go moldy and die off.

They receive sun in the late afternoon and early evening.

Any ideas on how to prevent or cure or even what the issue may be ?

I only water if dry, add a small amount of basket feed when planting.

Thanks. 

Yeah, did think it was a combination of the run off water and maybe too shady. It's facing south west.
Primroses and polianthus seem to be OK.

Thanks.