Late Winter into Spring
Prune existing roses and plant new roses in this season. Pruning is essential because it allows sunlight to reach the center and air to circulate around the canes. Steady airflow prevents fungal diseases.
Pruning: Look for swelling leaf buds on the rose canes; don't wait for the leaves to show. Start by cutting out branches that are dead, damaged, or diseased. The next step depends on the type of rose:
Once-flowering roses, which bloom abundantly in spring or early summer and then are finished for the year, need only winter damage removed.
Repeat-flowering shrubs bloom heavily in spring and continue blooming more modestly throughout the summer and fall. Cut out winter damage and cut the rose back by one-third to half of its height. Make these cuts about one-quarter inch above an outward-facing bud. Prune out thin, crossing, and inward-facing canes.
Climbing roses. Climbers bloom the way repeat-flowering shrubs do but grow canes 6 to 20 feet in length. For climbers, which are typically trained onto arbors or other structures, prune back laterals (stems that grow from existing canes, rather than emerging directly from the base of the plant) to between three and five buds. Don't cut the growth that emerges from the base--you want to encourage those canes to grow. With newly planted climbers, cut out only dead, diseased, or damaged wood for the first three years. Don't shorten any canes until the fourth season.
Rambling roses. Ramblers are similar to climbers but have a more sprawling, relaxed habit. They bloom once a year, and get big--10 to 30 feet big. Retain the strongest old and new growth.
Secure ramblers and climbers by tying the long, sturdy canes to supporting structures.
Planting: Roses need at least 6 hours of sun each day (with a little early-afternoon shade in really hot climates). Choose a spot with well-drained, fertile soil and consistent air circulation.
Plant bareroot and dormant container roses when you see the forsythia bloom in early spring. By then, the ground has warmed enough for planting.
Dig down 3 feet and replace the soil with amended, organically rich soil. This is especially important if you're planting a new rose in a place where an old rose has grown. Use soil from a rose-free part of your garden (or bring it in), and move the soil you take out to another rose-free area.
I take my grandfather's advice and put very well aged manure about 2 feet below soil level and cover it with about 4 inches of amended soil. The idea is to draw the roots down deeper into the soil in search of nutrients.
Soak bareroot roses in water for 3 hours or so before planting and keep them shaded for a week after. Wait until the danger of frost has passed before planting container roses that have leafed out.
Watering: At planting, water your roses deeply, and do not let the soil completely dry out until they become established, which means until autumn.
Mulch: Spread 1 or 2 inches of shredded leaves or bark chips around your new roses.
Feeding: For existing roses, cover the soil with an inch of compost, mushroom compost (my favorite), or aged manure.