I've seen that on mine here in W. NY. I just deadhead them. All the plants look healthy and are doing great. It seems to me that its the beginning of the flower dying off, of course, I'm probably wrong.
Just as Gracesmom has said, the Petunias are showing signs of the flowers going over /decaying / dying off. These are one type of bedding plant that needs constant dead heading to keep them producing even more flowers AND give a weekly liquid feed at one of the watering's you normally carry out.
Annuals, that is a plant that seeds are sewn, germinate, grow and flower all in the one season, nature tells Annuals to get growing, flower and then set seeds to reproduce for the following year wherever they drop there seeds either by wind, birds or humans that gather the seeds for sewing next years.
What we as gardeners have to do is keep picking off the decaying flowers to trick the plants into thinking it needs to set seeds because the flowers are fading, you pick off the dead / dying flowers thus also removing the chance of energy being wasted producing seeds as it's the flowers you want to keep growing more of instead of seeds, dead heading makes the plant make more flowers to replace the ones you removed dead.
the markings on the flowers is just natures way of beginning the decay / rotting flowers, Also do keep in mind once you allow the plants to make seeds heads it is never a great show of flowers there after as the energy has gone into seed making. jeeeees I keep going on about seeds eh, but hope you get the idea anyway.
In a nutshell there is nothing at all wrong with your Petunias except fading flowers needing picked off to allow even more lovely blooms to grow and replace the dead ones.
Hope all this helps you out.
Best regards. WeeNel.
I have found that about this time of year, the petunias tend to get leggy. They need to be cut back and fertilized. Cleaning them up and deadheading helps, but it is not the entire answer. If you want them to set seed for next year, there is still time even if you cut them back by half or so.
When I deadhead my petunias I tend to throw the cuttings is a pot with soil or in an area in the garden and I usually get seedlings coming up the following year.I was all in smile when I saw the million petunia seeds germinated at the base of the garage, they look so pretty I left them there all season. This plant was given to me by a friend 3 years ago and I picked up a lot of seedlings and also put them in hanging baskets and containers
The flower garden truly is a thing of beauty. Like many people I always wanted my very own. I didnít know where to start, what to grow, or even how. But once I got the basics down I realized that it doesnít have to be very hard. It can actually be very easy to grow your very first flower garden with the right knowledge.
I agree with you reinadeoz, your garden is your space no matter what size of ground you have, it can be as easy as pie IF you take your time to learn as you go, so many people want to grow hundreds of different types of seeds and wonder why they got nothing back, how can you tell someone they needed different conditions for different types of plants so well done you, teach yourself with a few types of plants and get it right, then move onto the next stage of gardening, it will reward you no end, dont go to ambitious at first or you put your tools away and give up,