media does wear out... leading to watering issues ... when is the last time you started the season with fresh media ...

how rainy has it been.. how often does the pot dry out to some extent???

it never hurts to include a big city location.. so we might gleen an idea of this seasons weather ....

the damaged flower also looks like someone might have sprayed something on it.. ruining the flower ... anyone around that may have done so???

ken

could be verticillium or fusarium wilt if it isn't root rot. i regularly lose most of my petunias and some other plants to these fungal diseases. I have resorted to microwaving the potting mix and strting my own from seeds with some success but then I slip up -a new bag of potting mix seems harmless and ehen the inevitable happens. If the roots are white and not rotten, one of these could be your culprit.

So, with these fungal diseases does it make sense that the middle sunpatien would be the only one infected if they are all in the same pot and soil?

They don't all get infected and die at the same time. The middle one is more likely to go first as it has the worst drainage and air circulation of all. I have one of my four snapdragons showing all signs of dying - yes, the middle one. Also, see how one of three petunias is gone. I have learnt from previous experience that trying to separate the good ones, replace potting soil etc. is useless. Eventually they all succumb. The fungus is understood to infect through damaged roots etc.

And this is most likely caused by the potting soil having these fungal diseases in it? Would it be possible that my compost does? I never even thought of the potting soil as I have always used Blooming Mix and never had issues.

Last year was when I first started using my compost mixed in, the sunpatiens didn't do this exactly but they started to suffer from "something" mid way thru season. I thought maybe my compost had caused it but I used it again this year and now this issue.

And now that I think of it...I composted last years potting soil as I usually do so if I used some of my compost again this year I wonder if the fungus survived our cold...below 0 winter?

The fungus would survive cold. Most would not survive proper (hot) composting but I am not sure if this one does or does not. Usually, it is the hot humid rainy conditions that trigger the infection. I got a bag of fresh potting mix recently and uppotted several plants without sterilizing the soil (it's presumabed to be sterile). No my petunias, penstemon, snapdragon, nasturtiums and stocks are going down one after the other and I am kicking myself for not nuking the potting mix (I microwave in batches for 8 to 10 minutes until the bag puffs up with steam. Temps are usually 200+ F. Let it cool before opening). The conundrum with using compost is that if one were to sterilize it, the good bacteria that it is supposed to add to the soil will be lost. If one doesn't then some of the pathogens that survive despite composting (those that are not killed by the process or survive in parts of the compost that never heated up during the process) will lurk around. Unfortunately, there are no good solutions. We'll draining media would be less prone to the issue. Otherwise just use sterile mix and start your own seed or cuttings because commercial plants may already have them lurking in their.... Another option is to grow only those plants that are largely resistant to these fungi. For example, I have never seen a Dipladenia or a purslane die like this, or a rose etc. Another is to just replace as and when you lose one. Unfortunately, if you replace with the same plant variety it will probably repeat the issue. Of course, at some point the growing season is over.

there is mother earth .. in which i include compost ... and there is potting media ...

and in my world.. warped as it is .. i dont mix the 2.. and i would never buy a media that says it has compost in it ... it breaks down.. its compost ..

think of media as a water management system.. holding / retaining the water requisite.. and shedding excess ... and as it wears out.. that system falls apart ... perhaps becoming mucky.. and not draining properly.. etc ... leading to plant stress.. root rot.. etc ...

this is why my first question was... how old was the media ...

after that... imo.. its the vagaries of ma nature... why one plant in the middle fails ... its very common.. and any dude or dudette that plants 20 arbs in a row .. its never the ones on the ends.. it always in the middle .... lol ....

i presume you have done this for years.. and i presume this is all new to you ... so im back to ma nature.. and the rains as being the trigger that probably started it all ... leading to drainage problems.. then plant stress ....

after you empty the pot this fall... see if it spot happens to be the furthest from drain holes or some such .... which would bring us back to drainage ...

ken

We have definitely had a hot, humid second half of summer. So that is a very good possibility for the issue. I know there's a drain hole under each plant in that rectangular planter but still...hot, humid, nasty.

I never thought about NOT combining my compost with the media. Actually, I thought hey, I can save $$ on media and use my compost. :( I was thinking this is the purpose of compost, right?

I've had issues every year with some phlox varieties with powdery mildew and some of the lilacs also but never a disease issue with an annual so this is new on me.

The variables are many but thanks for the ideas on what to look for.