As a comment about Petunia (Petunia exserta)
I planted a small pot of Petunia exserta in 2014 into a 20-inch container on our sunny patio, together with Salvia 'Elk Hot Tamale' growing in it. First time growing these two beauties. In 2015, I didn't disturb the soil in that container, and to my pleasant surprise, I not only had salvia Elk Hot Tamale blooming, but petunia exserta also! I'm hoping they both survive our winter and bloom for 2016 and I'm not going to disturb the soil other than gently pulling any weeds. Beautiful and bright flowers on both plants.