January through March is prime planting time
Inexpensive and very easy to plant, bare-root roses are sold by mail order and in nurseries between midwinter and the time roses first leaf out (around late January in mild climates, March in colder climates).
Most come with roots wrapped in plastic bags or tall cartons full of damp organic matter. There's a good reason: If roots dry, plants die.
Here's how to get bare-root roses off to a good start:
1: Unwrap the rose, shake packing material from the roots, and cut off the tag. Prune off broken roots or canes. Plunge the rose into a bucket of water ― its roots completely immersed ― for a few hours.
While the rose soaks, dig a planting hole about 2 feet wide and 1 foot deep. If your garden soil is reasonably good (not excessively sandy or heavy with clay), you won't need to amend it. If it's bad, mix 1 cubic foot of compost into the backfill.
2: Make a 10-inch-tall cone of soil in the middle of the hole, then center the rose on top of it, with roots spread down the sides of the cone. Pull backfill into the hole, firming it with your hand (never your foot) as you go.
3: When the hole is filled, water until the soil around the plant turns to mud. Rock the rose back and forth to settle it in and to allow air pockets to bubble up through the mud. This process is called "puddling in."
When you're done, the rose's topmost roots should be barely below the soil surface, and the graft (the swollen part just above the crown), if the rose has one, should be well above the soil surface.
4: After puddling, add enough backfill to level the soil. Make a 3-inch-high watering basin about 10 inches from the base of the plant. Stick a label in the ground beside the rose and you're done.