Welcome to the forum!
Petunias like lots of sun and water! Deadhead the spent
flowers for more blooms and mid-season, when the
plant begins to look leggy, prune them for bushier new growth. Don't worry if you think you've pruned too much...they're fast
growing and very resilient.
In early autumn,
seed pods begin to form - they look sort of like hard, brown buds, which start off closed tightly, but as they mature, begin to open slightly at the top. When the pods are just beginning to open but before they disperse all the
seeds, pinch the pods off and shake the contents out onto a piece of white paper. Petunia
seeds are black and very tiny, similar to poppy
seeds. When the
seeds are dry, store them in an airtight container or
seed envelope (don't forget to LABEL them!)
Then in the
spring, you can sow them directly outdoors or start them inside about 6-8 weeks earlier. Because the
seeds are so tiny, I just lightly sprinkle them directly into the soil and lightly tamp them. Petunias don't take long to germinate (can't remember how long though) and are easy to grow. You'll probably need to thin them if you scattered the
seed. I hate wasting the
seedlings I've thinned, so I just transplant them elsewhere (don't know if this is good gardening practice or not but it works for me).
Two most important things to remember are sun and water! They'll begin to droop quickly if they aren't getting enough water but a good soak usually perks them up in a few hours. Good luck and keep us posted how they do!
P.S. I've never grown zinnias and I only recently have acquired an indoor gerbera daisy which I'll
plant outside in the
spring (if it's still alive
) so can't help you on those!
Welcome RLR,
duckie
) 
