The best time of the year when to prune roses depends on the region and climate zone.
Finding the right time to prune roses shouldn’t be a problem. Except for once-blooming roses, spring is the best time to perform the annual prune.
Many rosarians start too early with that important task.
After years of observation, I have learned that it makes sense to wait until the buds start to swell or show several red leaves.
The correct time may be May in several regions with colder climate, but early January in warmer regions.
The later pruning will bring back better results compared with earlier pruning and provides several advantages to the rosarian:
Many experts recommend a pruning in late fall or even winter. I do not back that opinion.
The pruned rose trees may suffer from frost damages and in the end the bud eyes at the bottom parts of the roses will grow too early in spring and may face frost again.
If you really want to do something good on your roses in fall, please cut them a little bit. Prune long canes and thin out lateral growth to avoid damage or breakage during winter winds.
The best time to prune roses depends on where you live. The USDA developed a plant hardiness Zone map, based on the temperatures recorded across the States. To determine in which Zone you live, please use the map provided on their website. (http://planthardiness.ars.usda.gov/phzmweb/interactivemap.aspx)
With the background in which Zone you live and knowing the frost dates will help you identify the right time for pruning.
For an overall view, I figured out the approximate pruning times for the different hardiness Zones. Anyway, whether you are not sure when to prune roses, contact your local rose society, they will help you with that topic.
Zone 4 and below
In Minnesota, North Dakota and most parts of Montana temperatures go down to under -20F and frost in late April and May is not a rarity.
In these regions the pruning time will move sometimes to early June.
Zone 5 & 6
Temperatures range from -20F to 0F in regions like Indiana, Iowa or Illinois and the pruning time can be set between April and May
Most districts of Tennessee, Maryland or Arkansas are part of this Zone. Temperatures from -5F to 10F allow us to prune the roses starting mid-March.
Temperatures in South Carolina or Mississippi rarely go under 5F and the pruning time will start in February
Zone 9 and above
In West Texas, parts of California and Florida temperatures rarely go down to 15F. The pruning time here may be in early winter, right before the cool weather with rain arrives.
To grow roses in hot climates like Hawaii may be challenging, but it is possible. In lack of seasons and since there is no dormant period, roses should be pruned year-round after florescence.