In New Hampshire, I have seen people begin to harden them off two weeks before the average date of last frost (around mid to late June) so you should do similarly in MA. Move the plants outdoors on a warm day to a shaded (bright shade) place. Then bring them back inside before temperatures cool off at night. Repeat; then gradually, move them out to get brighter morning light and expose them to more wind, but continue to bring them in at night. Transplant them to the garden or into baskets once temps at night have settled in a warm range (say, maybe 55-65F). Then overwinter at the end of the growing season or get new ones in Spring 2022. You can overwinter in late Fall when they have gone dormant. Note that these guys tend to develop root rot easily or die due to high-low temps so, do not feel bad if this happens, specially at the end of the growing season, when either early frosts arrive unexpectedly and when one is "stuck" watering at summer watering levels but the temperatures have receded and the plants end getting with root rot. Hint: water the soil and never the leaves when the soil feels dry at a depth of 2" in order to minimize fungal issues in the leaves (mildew, etc.). Watch out for some worms that may cause leaf drop.
