I can't answer all your questions but remember that those plants you buy that look so beautiful have been grown by professionals under ideal conditions. I'm sure they use special fertilizer and in some cases they cut them back to produce a large flush of bloom for the market. As homeowners living in the real world where flowers are not grown in greenhouses we can't always get the same results.
There are of course exceptions. If something really isn't working for you then try something else.

I don't know anything about wild petunias but hybrid petunias can't take the heat/humidity/rain/fungus of our summers.

Forcing a plant to perform outside of what it normally will do is a sure way to shorten its lifespan. Adding more chemicals to your groundwater by over-fertilizing is a sure way to shorten yours.

Wild Petunias aren't really in the same family as hybred petunias, at all. They are a native form of ruella. Mine are blooming like mad.

What Laura said...

And also, commercial growers grow to sell. The varieties they use are those that they can dazzle the eye with as quickly and cheaply as possible. And as many commercial outfits do, the sale is the thing; not whether they perform well for you.

Plus, they are notorious for selling plants at the wrong time of year!

Tom, although I agree that commercial growers are in it for the quick sale, I think you've asked a good question. I use a standard 10-10-10 type fertilizer for everything but often wonder if I would get better performance from my plants if I used something else. They grow like crazy but I've thought there was a reduction in blossoms this year. I haven't decided if it's the wrong fertilizer or more shade from the trees.

And where's the line between feeding your plants and over-feeding? I honestly don't know.

Kate

every nurseryman knows the same line.. 'if it ain't bloomin', it ain't movin'"

i should be more consistent in fertilizing. i usually buy a high-quality lawn fertilizer with slow-release N (from lowes, it's 18-0-8). it's cheap and has micronutrients.

most fla fertilizer has a very low P ratio, in part b/c florida sands are rich in phosphate rocks (huge phosphate mines in the tampa area with predictable horrific results for the environment), in part b/c phosphorus causes serious problems in our lake/river system (point in fact, lake kissimmee).

that said, vegetables and fruits and flowers (not lawns) need some P and more K (potassium) than lawns. i kinda would like it if all the compost and mulch i used added the needed macronutrients, but they don't--a couple months ago, after christine's urging, i added some superphosphate to my usual fertilizer regime and it made (i think) an immediate impact on my fruit trees--they all put our some new growth, and my figs immediately threw out scions from the roots. interesting. i think they were P deficient. i've also noticed a bunch of new fruit set on my pepper plants.

i'm told it's impossible, or nearly impossible, to add too much phosphate. plants absorb it VERY SLOWLY. that's why it's such a problem--there's no harm to using too much phosphate, so people overuse it.

since i use a lawn fert in my beds, two or three times a year, i throw down some muriate of potash, which is for all intents and purposes an organic source of K (potassium). i also regularly add epsom salts to all my roses and vegetables.

one final thought: never add nitrogen to trees that are setting fruit. it's a sure way to cause them to drop that fruit, as my persimmons can attest.