Lunarpunk

Maybe you know all this, but for anyone wanting to learn how to grow plants, here are some thoughts.

Don't move it around or mess with it. It can takes weeks, months, for a plant to steady up. I've had plants finally take off after a year of "neglect". The more you try to improve conditions, the worse the results. Mom couldn't grow shit and was wholly ignorant, yet plants from dad's funeral 30-years back were thriving. She put them in place, never changed a thing, not even to rinse them off, and always used the same exact watering and feeding regimen.

You're going to have light issues inside. I can go on for ages, but what our eyes perceive as bright bears little relation to received lumens. Go outside on a cloudy, dark day. Lay down and stare straight up. Then you'll think it's bright. Also consider, a sunny day on winter solstice is dimmer than a cloudy day on summer solstice. Our eyes lie to us.

Think on this: Tropicals are mainstays of the houseplant world because they evolved to grow under 3 canopies of rain forest. Our "bright" windows are often barely adequate and a petunia needs real light.

Put it as close as you can to a south window, west is second best, leave it. Only water when you can stick your finger in an inch and come out dry. That's it. No touch, bad touch! Once it acclimates, then you can experiment with feeding it.

Another pro tip on water: Tap water, while fine for us, is full of crap. Blast some in a pitcher and stick your nose right up to it. You can smell the chemicals. I catch rainwater and bottle it, but you can also let your pitcher sit for a day, even better in the sun. Now the water smells "flat". Makes a dramatic difference, try it!

And you're spot on. Shipping beats hell out of plants in the best scenario. Consider: The roots you see are not what's taking in water. It's the microscopic hairs doing all the work, and those break easily.

And I'm sure you're right about them being finicky. Not only is that meant to be a sun-blasted outdoor plant, who knows what was genetically changed to get the final product. As an example from my own experience, exotic peppers are far more picky than their "base" relatives. They're bred for heat and funky fruits, not toughness. I suspect these petunia's are the same, emphasis on the cool factor more than hardiness. Does that make sense?