Don't give up on the mini roses! They perform better outdoors. I am in the same zone. Some grocery store minis have died quickly for me, but most do well. The red and white striped one survived its first winter here. The most problematic ones for me were the peach and the white ones. I wish they would label the minis by name, but then they would probably have to raise the price. The local grocery store typically has a selection near the entrance. Prices fluctuate from $1.99 - $3.99.
I followed Lyn's excellent advise on mini and other roses as I moved into a new garden this year. Concentrate on growing healthy roots.
Follow Toni's advice and separate the 3-5 roses in the original tiny store pot when planting them in a larger pot with good soil. The roses are root bound in the little store pots. I added Bayer systemic 3 in one granules to the soil. Mini roses can be susceptible to blackspot in humid climates.
In winter, cover them with peat moss held in place with mulch or leaves once the ground has frozen. Don't worry about snow cover. Roses like the extra protection. As spring arrives, gradually remove the covering. Feed and water them like regular roses.
