Hmmmm. The soil borne disease that is relatively common among bedding plants (in general, but not petunias in particular) is phytophthora. This fungus is absolutely ubiquitous in most soils all over the place. But soil conditions need to be present in order for a plant to fail because of phytophthora infection. Soils that are over watered, consistently moist, poorly drained, etc. are what will trigger a problem.

Fertilization will not assist a plant in fighting off the disease once it has taken hold. Creating a raised bed, perhaps, if the area stays a bit soggy will help. And trying some other annuals other than those known to be susceptible to this disease. Petunias is on the 'prone' list.

Pathogenic diseases need to be identified before you think about a chemical treatment...if that's what you are looking for. You don't want to be making drenches with chemicals when they will be totally useless against the problem.

This explains everything!!! The first year I planted wave petunias, they were gorgeous. The past 3 years they died off very early. I tried everything- fertilizer, water, insect and fungus sprays. Nothing worked. Finally I replaced the plants only to have them die off again. Grrrrr!!! No more petunias for me!!! This year I hope to get a similar effect with verbena homestead purple and some annual trailing hot pink verbena.

Just don't forget....take a good look at the site conditions to make sure that other plants might not end up with the same problem. Over watering, saturated soils, etc.

Good luck!

I've had the same thing happen and have about given up on petunias unless they go in new locations or pots where the soil gets changed.

I have grown petunias in the same spot for about 30 years....never had any problems. I use lost of my own compost, so maybe that makes a bit of a difference....or I have just been lucky!
Linda C

I planted 4 purple waves last month ...three are gone. All other annuals, perennials and plants look great (and I have a lot of plants with good air circulation) The petunias did go in roughly the same spot as the last two years...
somebody please kick me!

On the bright side, several waves from last year came back!

I have had the same trouble. However, marigolds seem impervious to the disease. So are portulacas, so long as they get some warmth and plenty of sun. Geraniums do well, too.