It seems like the best time to plant roses is in well-drained soil. You need a PH testing kit available at gardening centers to test the soil. They  are not  very expensive. You want a PH of 5.5 to 7.0

It's safe to plant after any danger of frost is gone.Plant your roses in an area that is well-light in the morning. Roses require a lot of sun light, at least 6 hours. 

When you plant your roses in the ground for the first time, be sure to soak the roots and surrounding soil. Soak the surrounding soil for the new few weeks on a continuous basis. After that every two week the bed should get a good soak. If in a wet climate, water less often; dry climate, more often.

 Place a lot of organic matter surrounding the plants to insulate the soil temperature and prevent evaporation.