crape myrtle in pots

[Boothbay]

I have this hardy crape myrtle plant in my backyard garden for 15 years and blooms each year profusely. Last spring, I noticed some 'sprouts' around its base and I removed t hem root and all and put them into various size pots. I brought them indoors last september and nutured them and they looked healthy. BTW, I live in the nyc area..zone 6 or 7. A couple of weeks ago I started to put them outside on a small patio to get adjusted to the outdoors when it finally does get warmer. I bring them indoors at night although they are suppose to be hardy. I'm talking about plants that are almost 2 feet high. In one day, I noticed that the leaves look like they have been 'toasted' by the sun. The temp was merely in the low 60's during the day and low 40's at night. I immediately brought them indoors and the leaves started to recuperate. Why does this happen to a so called hardy plant? When will the temperature be right to leave them out altogether, if at all?

[Vox Humana]

Plants that have grown indoors for extended periods need to be acclimated to the outdoors. I put them in a shady, sheltered area for several days before exposing them to direct sunlight.

[Travis]

You should have left them outside to begin with by burying the pots in the ground over the winter.