Miniature roses are generally as hardy as hybrid tea roses. But because yours are growing in containers, you'll need to protect the root systems from low winter temperatures. Plants will be fine in the pots without any additional protection until the temperature dips into the low 20s. In fact, exposure to some frosty nights will help acclimate the plants to winter hardiness. One option for overwintering your containers of miniature roses is to move them to an unheated garage where they will be cold but not freeze. Check the plants periodically through the winter to make certain they don't dry out too much. The soil should be moist but not wet. Another option is to sink the pots in the ground in a protected location outside. Cover the pots and plants with a mound of soil. Mulch with leaves, straw, or wood chips. In early spring before the buds begin to grow, dig the plants and repot for the coming season.