Some help with how I deal with this problem would he helpful.thanks in anticipation of a reply
PH

I have had the same problem every year. I put it down to not planting the roots deep enough. This year I haven't watered the flower borders at all, only the pots, and have had no problems with mildew.

Water.

I tried soaking mine with water every year, and it still succumbed to mildew so this year I have totally left it alone and hey presto - no mildew! Works for me!

Worthy's right - its probably dry at the roots. Powdery mildew is common in dry conditions, so give it a good soak at the roots and if you want to clear the mildew with treatment, mix 1 part milk to 9 parts water and spray all leaves (including the backs) and stems with this.