For nine years now I've relied on this annual pruning schedule for my beds of Knock Out roses:
Do you agree with that schedule? This year, my roses are pretty beat up from the long term heat. They were spectacular in April-May. Now, leaves are falling off and blooms are not popping back after I trim off the dead ones. My typical cases of black spot are showing up, even though I try to spray every 2-3 weeks. More leaves fall off.
Any suggestions or should I adjust my pruning schedule? Prune now? Thanks for any tips.
The scheduling is great – heavier pruning in late Jan to mid Feb (the mid Feb date is commonly used in north La, the late Jan date in south La, but you may prune anytime during that period), and a lighter pruning in late August or early September (the late Aug date is commonly used in north La, the early Sept date in south La, but you may prune at any time during this period).
The degree to which you are pruning would be considered rather severe for Knock Out roses. The heights you are using apply more to hybrid tea and grandiflora roses. Research indicates that Knock Out roses respond best if not cut back lower that 24 inches for the hard pruning in early spring, and more moderately in the fall. I’m surprised they have done well cut back as short as 12 inches from the ground.
But, real life experience is the best test. If you have been doing this for several years, are happy with the results and the roses are doing well, you needn’t change a thing.
Your current problem has nothing to do with pruning – it is a heat issue. Roses do not like it when day after day hits the 90s. You cannot change this. Roses don’t look as good in late June, July and August as they do in April, May, early June and October, November and early December – and they never will no matter what you do. The leaves may be duller, the flowers lack vibrant color, are smaller and don’t last as long. Some roses stop blooming.
If you prune them now and force them to send up new growth, it will occur in the hottest time of the summer. The worst thing we can do to a rose bush suffering in the heat is whack it back. That just adds to its misery.
Feel free to deadhead. If you think you need to control the size some, deadhead with longer stems (click here for more information).
I would not be worried in the least about black spot on Knock Out roses. They will get over it. If it bothers you, increase your spraying frequency. Check the label of the product you are using and spray regularly at the shortest recommended interval.
Click here for additional information – let me know if you have any questions.
Consumer Horticulture Specialist
The LSU AgCenter and the LSU College of Agriculture