Actually, gardenias are tough, tough plants. I don't know why they have the reputation of being hard to grow, I guess because too many people have gotten a small, potted one and then proceeded to torture it by keeping it indoors in hot, dry, dark conditions, and then often overwatering and rotting the roots as it sat in a decorative pot cover -- the typical Valentine's Day/Easter/Mother's Day gift plant thing.

They should bounce back with vigor. I would just pot up to a larger, appropriate sized pot, use a really good quality potting mix like ProMix that is peat and perlite based, and keep them watered. They like to get just barely dry between waterings.

I assume you're going to keep them outdoors for the summer -- they will be ok in full sun to partial shade, as long as it's not cooking in extreme afternoon heat.

I a few weeks as they recover, I would start feeding about every 10 days with a liquid fertilizer for acid-loving plants. Use some Osmocote, too, if they don't have some from the grower already. The two biggest issues you will encounter with gardenias is 1) that they turn chlorotic easily if the soil pH goes too high, that is a problem in areas with hard tap water, use acid plant fertilizers and trace elements to combat this and 2) they are bug magnets, aphids, scale, white fly, and mites love them. I spray a couple times a year with one of the newer class of insecticides/miticides such as Bayer 3 in 1 Insect/Disease/Mite spray. And I always put imadicloprid in the soil spring and fall. That keeps bugs away.

The winter best in cool, dryish conditions. They are temperate zone plants and need a dormancy, but they can't tolerate deep freezing to any significant extent, most are zone 8 or zone 9, such as the really common variety 'August Beauty' which is probably what yours are. I winter mine at about 40-50 degrees, let them get quite a bit drier than in summer but don't let them wilt. When I bring them in in the fall, I generally will prune the top back about 50% just for size control, since they grow rapidly in the summer and my space for wintering is small, but that is completely optional.

Yeah my gardenia was in a pot in the shade for YEARS with very few flowers and yellow green leaves (probably due to being root bound and a little neglected). Last year I put it in the ground (and this ground is very lacking of nutrients). This year it is green with tons of flowers.

Next year Im going to concentrate more on container gardening. All my older plants are in containers and suffering. Ive been reading about root pruning vs. potting up. Next spring Im going to take all the oldies out for a good pruning. But the gardenia made it into the ground. Sometimes when I sniff a gardenia I almost pass out because of the potency.