Garden Pests and Diseases: Petunias dying soon after planting.., 0 by Gitagal

Gitagal wrote:
I know it is July--I also know that we have had a horrendously hot summer (High 90's)
with almost daily drenching rains. This has been going on for about 2-3 weeks now.
The gardens are suffering--and many things are giving up the ghost...

However--I have tried to plant some petunias where there are some open spots--
most of which already had petunias in them that died a similar death.
These have been purchased from different sources and all looked
OK when planted, Then, within a week, they just shriveled up and died...
The stem were void of leaves--just looked dried up and dead.
Other plants nearby were not affected--even other petunias planted earlier.

OK! I know it is end of season--and, even at Nurseries, the plants are so-so.
Good deals to be had, though--and the flowers look OK--so I buy them.

One person suggested I may have nematodes in the soil--but this is happening
in 3 different beds a good distance from each other.

Could I have someone's educated guess what may be going on here??
Just FYI--I am a seasoned, informed gardener--but am lost in this case.
WHY is this happening????
Thanks, Gita

The last picture is so sad---these have been blooming beautifully, and now,
on the sunnier side, after another 2 days of rain--this is happening.
I really think, just in this case, they are simply dying from all the heat and water,,,
The same blue petunias, on the other side, are still OK. More shaded...
Pic. #4 shows the bed as it was...

Thank you, Gita