Have I ever killed off indestructible perennials? It might be faster if I listed the ones I didn't kill.

Took three tries for
Lily of the Valley. Now I can't get rid of them. Took three tries for LOV pink variety -- still none surviving.
Comfrey? Two tries and counting -- no comfrey yet.
Roses. DH built a formal rose garden for me/us. Roses didn't like it, I presume, since only one of 20 survives -- and that was a not ordered shrub rose.
Monarda. Killed it out of the turn-around. Killed all four varieties out of the sunny perennial bed. Most of the monarda in the semi-shade garden seem to be gone.
Mums. I have purchased mums so many time only to have them all fail to survive the winter.
Hardy Carnations? Nope! Not hardy here despite what should be great growing conditions for a zone 4 plant.

Gillardia, Daisys, black-eyed Susans, Scabiosa, Lamb's Ear, Heuchera, Cardinal Flower, Hardy Geraniums, (I should just go through my plant binder, but I haven't the time) and Phlox are among some of the easiest-to-grow perennials that I have managed to kill off over the years.

Then came my Epiphany! Red's Rules for Gardening.
Rule one: 
a plant's chance for survival is directly related to its cost and the time invested by the gardener. The more expensive and the more attention the greater likelihood of plant failure.
Rule two: 
Give a growing condition even close to what a plant needs and the plant will do what is required for its survival.
Once I started plopping the plants in unprepared ground and ignoring them a bit, everything I planted began to do well.

Now I get the roots close to the soil, let the plant know it's "grow or survive", and expect the plant to do the rest. Seldom fails to produce thriving plants, seedlings, cuttings, grafts, whatever I try.
