How to Plant Potted Roses
Plant a potted rose early in the growing season (late spring or early summer) — about the time you generally find them for sale. If your climate is cold, wait until after the last frost. But don't wait too long, simply because hot summer weather stresses a freshly transplanted rose plant.
Good soil is also very important. It should be rich in organic matter and drain well. If it isn't, import some good loam (rich, crumbly soil) and compost, or at least mix the existing soil half-and-half with premium soil.
Preparing a hole for your potted rose
When planting roses that come in containers, your first order of business is preparing the hole:
Eyeball the pot the rose came in and dig a hole a bit wider and deeper.
You can set the pot in, plant and all, to check yourself.
Loosen the soil on the sides and in the bottom of the hole, using your fingers or a trowel.
This way, the roots can head outward and downward more easily when they're ready.
Getting a potted rose ready for planting
You can't just plop your rose into a hole, add the soil, and call it a day. Prepare the plant:
Water the plant well — until liquid runs out the bottom of the pot — before planting.
Groom the top half of the plant.
Clip off damaged stems, flowers, and buds. Leave on as much good foliage as you can. You can cut down to the highest five- or seven-leaflet leaf group. Cut to an outward-facing set of leaves to encourage new growth away from the center of the plant.
Run a butter knife, ruler, or other similar flat object all the way around the inside edge of the pot to loosen the plant.
Squeezing the container sometimes helps. Gently pop it out.
Planting the potted rose, finally!
And here's how to plant:
Rake your fingers up and down along the root ball to loosen the soil and roots.
Don't fret if a few roots break off.
If the rose is really root-bound, take a moment to help it further.
Score the sides of the dense rootball with a sharp knife, up and down, in two or three places. Don't make a deep cut — just 1/2 an inch in is fine. This step stimulates new root growth.
Holding the plant by the rootball (not the top growth), set it into the prepared hole, and backfill good soil around it.
Make a basin of soil or mulch around the plant when you're done; then water.
The basin should be about 12 to 18 inches in diameter so the water that it collects soaks in directly over the root zone of the rose. This basin makes for easier watering (which you should do right now — give it a good soaking). If the plant settles too low in the hole after the watering, wiggle it back up.
For a grafted plant, mound soil over the bud union to serve as insulation to protect this vulnerable portion of the rosebush.