What's there now?

By grooming, I mean dead heading faded blooms and trimming off brown leaves. Trim back any unruly growth. Petunias spread out quite a bit when they are well tended.

Regular fertilizing is a must. Fertilize when you plant them. I use a slow release granular fertilizer when planting and liquid fertilizer later on.

Mulch with finely ground bark/soil conditioner and replenish it often.

Water your plants regularly.

There are so many beautiful petunias! You’ll be able to find the perfect red, white & blue shades.

Good luck!

I live at high elevation with occasional hail, I quit gardening a couple years ago. But in response to the OP, asking what flowers might be suitable for the purpose they have in mind.

It must be challenging to garden in that environment.

I think your petunia suggestion was excellent! They love the heat and humidity where I live in the Southeast. A few years ago, I grew a salmon colored variety. 🌺

one of the few species that do.