Cutting them down probably would not hurt them if the foliage is brown and crunchy already. They will probably show some new growth at the base of the plant.

Please do!...If you allow them to set seed you will have little baby mutt phlox all over next spring.
But only cut them down to about 12 to 18 inches. They will then sprout side shoots and put out a little more bloom.
Linda C

As long as the plant is healthy I leave it and it will bloom some more not as much as before but it will bloom. I know it looks a little messy but be assured it will bloom again, have had these for many years. When they are really dead looking, then yes cut them back. What I do in the Spring when they first get big and ready to bloom is spray them with WILT PRUF that stops alot of the mildew. To me. that is the majic potion with phlox, and I have alot of them because they are so pretty and love them in the background of my garden. It may not say WILT PRUF on the bottle but look for mildew preventive. I have both. Good Luck. Tricia

Tricia, I keep forgetting about that Wilt Pruf. I first read about using it on roses that get pm. I don't have that problem, but my phlox do get it. I've got to make a note of trying that next Spring.
As for cutting them back, I do that also. This year I also cut the front ones back in Spring so I have a staggering look. It's turned out well. As for letting them go to seed, I try to cut them back as soon as the flowers are done, but it doesn't always work out that way. I've had quite a few seedlings this way and I love them all. I've got all different colors now. They smell great too. But you don't want to let too many grow because they do need good air circulation. I have smaller plants in front of my phlox, so they help to cover up the bad leaves. Even with the pm, phlox are one of my favorites. I have them around my deck and when I come home on warm nights, it smells so good.

Kat

Thank you all for responding. I cut them down before actually reading your suggestions. My garden looks better without the brown leaves. I will definitely get the Wilt Pruf you suggested! I think my Bee Balm and one Azalea now have powdery mildew too. So I am looking forward to next Spring so I can try to prevent this from striking my Phlox.

Here is a link that might be useful: Wilt Pruf website

For years and years I have used 1 part skim milk and 9 parts water - mixed that together and then spray away on the phlox, lilacs, roses (for black spot), asters and so forth - just anything that will get powdery mildew. Instead of going to just specific plants I just start spraying at one end of the gardens and go to the other end - hitting all the plants as I never know where the PM will strike. It is inexpensive and it works - and it has worked for me for many years.

I have one phlox that I was given in the spring and I didn't treat it immediately. It (PM) zoomed thru that poor plant before you could say "phlox". I pulled off the dead leaves and sprayed down the plant and soil with the mixture and it put out new growth and is blooming beautifully. I also cut back most of my plants to make them bush out and not get so leggy (just as with mums) and they reward me with tons of blooms.

Just a suggestion.

I've heard about the milk mixture also. How often do you have to spray? I've heard good results with it, but if it's something you have to spray every couple of weeks, I'll probably get behind on it. I have quite a few. I remember hearing with Wilt Pruf you have to remember to spray the new leaves. But once they're sprayed it should last the season.

Kat

I have a white phlox, White Admiral, that NEVER gets mildew. I wouldn't be without it. It's blooming now for the 2nd time, in spite of over 100 degree heat for nearly 3 weeks.