You can absolutely plant a live rose in the fall, but keep in mind that dormant bare root plants are a safer bet. They're less shocked by the transition. That said, they can be difficult to find in the fall.
A: In Southern California, it's never too late to plant rosebushes. The popular “Iceberg” roses are super hardy and will rebloom without constant deadheading. They are also available in pink and burgundy flowered varieties. If you want to plant any perennials, it's a good idea to do it sooner rather than later.
Additionally, roses planted in April and May are doomed to face the upcoming summer heat sooner than later. Roses planted in February and March are able to establish roots while the weather is mild and are able to deal with the heat better once it arrives.
The best time to plant knockout roses is in the spring or fall. Make sure there is no threat of frost or they may not last through it.
In-ground: Add 2-3" of mulch, leaves, or pine/fir boughs around the base of the plant. A heavy snow cover will also help insulate and protect the plant through the winter. Also, the winter winds can really dry out the plant so you may want to wrap the plant with burlap.
About the only time not to prune is late summer and early fall, as this might encourage late growth that wouldn't harden off in time for winter. In the North, winter is not a good time to prune, but winter is just fine in the South. Although 'Knock Out' is marketed as a compact shrub, over time it gets pretty big.
Roses thrive on direct sunlight. For best results, a minimum of four hours of direct sunlight is recommended. However, even when planted against a north wall (meaning no direct sunlight) roses can still perform well.
Most roses can withstand a quick cold snap of temperatures down to 10 degrees F, but it is best to protect them if you expect an extended period of time when temperatures dip under 20 degrees F. The amount of protection your roses need depends on the climate in which you live.
Ideal Temperatures for Planting Roses
Consult your local agricultural extension service or garden club for information on the proper date. Roses cannot withstand temperatures below 32 degrees F, so keep plants awaiting transplanting in a warm, protected area where they will not be damaged.
When Do Roses Bloom? Roses start blooming in late May and continue to do so through early fall. They are often considered to be at their best in June, which is why roses are considered June's birth flower.
Bare root roses should be planted between November and March, while containerized roses can go into the ground at any time of year. If possible, opt to plant roses in bare root form in winter or early spring to give your new roses the best possible start.
First, dig a small hole where you want to put your new rose bed. Then, fill it with water and see how long it takes to drain. If it takes more than an hour you'll want to improve your drainage by digging deeper planting holes and adding some coarse sand to allow for faster drainage.
If you want to do any cutting of your roses in autumn, wait until after the first hard frost (temperature below 25 degrees Fahrenheit overnight). If you cut back before the first hard frost, it may send a signal to the roses to grow when they should be going dormant.
Apply a granular slow-release fertilizer such as Miracle Grow to the newly planted rose bush. A healthy application will help it recuperate from its replanting and adjust to its new location. For lush growth, continue a monthly application until cooler weather in the fall.
Blooming and Fertilizing
Knock Out® Roses will repeat-bloom from spring to frost regardless of deadheading. Deadheading does offer a cleaner, tidier look. Often people choose to deadhead to remove the faded blooms.
Water the new shrub once every three weeks for the winter and then once a week through spring. From early spring through fall, most established roses will need a good slow drink of at least 2 gallons of water each week. Mature climbing roses or larger shrubs may need 4 gallons each week.
In the fall, take off about ⅓ of each branch that you cut so your rose bush can grow healthy and tall in the spring. You can cut your rose bush down even more if you'd like to change its shape or height. Make sure to leave at least 6 inches (15 cm) of branches above the ground so that your rose bush can grow back.
Watering your roses is still important during the winter months. Even if your area does not normally get snow or ice, cold wind and air can pull moisture out of the rose's canes – meaning the soil moisture can also be depleted. Check your soil on a warmer day and give it a light watering if it's needed – do not soak.