ON OUR NEW FORUMS, Dan asked a great question that reveals a tip you can use right now to prevent powdery mildew this summer on your garden phlox:
“The biggest problem I encountered was with the Phlox I planted,” Dan wrote. “The leaves developed a terrible fungus and it slowed its growth terribly. When I first spotted it, I did some research and decided to use an organic fungicide. That worked alright, but the fungus came back. Then, I tried an organic remedy I found on the internet: spraying with a milk solution. That worked less well. The poor plants were so overcome with the black fungus that they eventually withered without flowering late in the summer. I finally cut them down. Now they are starting back with strong green growth and I’m pleased, but I wondered if you had any advice for treating Phlox fungus.”
THIN TO IMPROVE AIR CIRCULATION
One of the best non-chemical ways to deal with powdery mildew, I replied, which Phlox paniculata is so prone to in our humid summers, is to prevent it by improving air circulation in and around the plant.
Do this as shoots emerge by “thinning” the clumps—just use your finger (or a pruner if need be) to knock out like a third of the shoots, to space the remaining ones less closely together. The plant will breathe better, so to speak, and that will help prevent the fungus from overtaking it.
Another good preventive step is to spray starting before the outbreak occurs with a homemade anti-fungal like a solution of water, baking soda and horticultural oil. Rosarians do this with their roses to prevent black spot, another fungal pest; recipes vary but it’s approximately a teaspoon of baking soda and a teaspoon of horticultural oil (from the garden center) in a quart of water, or a tablespoon or so of each in a gallon. Other gardeners swear by horticultural oil alone.
Another truly preventive method: Grow mildew-resistant varieties, which give you the best shot of success. The Chicago Botanic Garden’s Plant Evaluation program is an excellent source for PDFs on the best cultivars of many kinds of plants, including Phlox (click on and download Issue #13 PDF at http://www.chicagobotanic.org/research/plant_evaluation/).
Ask, or answer, Urgent Garden Questions on any topic on A Way to Garden’s new forums. Look forward to seeing you there.
garden tip: first, make things worse 
february garden chores 
Phlox ‘David’ is a great cultivar that’s powdery-mildew resistant. Give it a try.
Yes, and a beauty–thanks, Hilary, and welcome to A Way to Garden. For those who have not seen it, ‘David’ is white-flowered, and maybe 3 to 3 and a half feet tall. Great suggestion.
M.
I have PHLOX DAVID. about 30 plants also they are all infected with powdery mildew. i did not see them until all of the plants go mildew and now i spray it with Defender i don’t see any improvement but all the top part of the plant is nice and green i also have cut up all of the leafs that has mildew. i wonder if they are going to bloom this year.
any ideas
Thanks
marina
Marina, welcome to A Way to Garden. Wow–30 plants of a supposedly resistant variety all mildewed! Not so happy-sounding. If the tops are good and healthy and green, there’s reason for hope, however. Like so many things in gardening, one has to just wait and see. Keep them stress free from here on out if you can, watering when dry and so on.
I found a suggestion online to deal with powdery mildew on phlox – milk!
You use 1 part milk to 9 parts water, put it in a squirt bottle and spray it on all the parts that are affected.
It’s almost miraculous in the way it makes the mildew vanish – it’s not all permanently gone yet from the plant, but enough disappears with each treatment to keep the plant going through bloom season.
It seems to act as a foliar feeding as well for the phlox.
Welcome, Jennifer. What a hilarious twist on home-remedies, isn’t it? “Got Milk?” taken to a new meaning. :) Hope to see you soon again.
I cannot find the answer to this question: will phlox rebloom after it has been cut?
thank you,
lois
Welcome, Lois. I assume you mean tall garden phlox, Phlox paniculata, which in the Northeast is a high-summer thing (like around the last few weeks). The answer is no in my experience, which makes sense if you look at how/where the blooms are produced (and how there are no buds the rest of the way down the stems to call into subsequent action).
Hi all,
I am new and do I sign up here or just pop in?
Lisa
Welcome, Lisa. Here you can just say hello, ask or chat away! On the forums, if you register (give username and email address) you can ask/answer freely (for free!). Enjoy!
Just thought I’d let Lois know that I have cut the dead heads back after blooming on almost all the varieties of Phlox I have and mine have bloomed a second time. I have been able to keep them going until nearly frost.
Welcome, Mary and that’s fantastic. Mine bloom and bloom…but always from up top, or close to there (so I don’t cut hard into the stems the way I would cut back some other perennials way down low). Thanks for the updates, and do come again soon.