Recently a member of our staff was talking to a friend who was busily preparing their roses for winter by pruning them back. He returned to the office somewhat concerned that it might be too early. Chances are, his concerns were merited…mainly due to the protracted summer/fall season we have seen in the Ohio Valley this year. But it does bring up the question, when should you prune your roses back ans what harm might you do if you prune too early. With that question in mind I sat down with the president of Monty’s Plant Food Company and talked with him about pruning roses.
First, let’s establish when roses should be pruned. In growth zone 5, where Monty’s is headquartered you generally want to do that sometime after mid-September. Though the calendar should be used as a guideline, not a hard date. What you are looking for is to prune sometime after nighttime temperatures start falling into the upper 40-degree range-if not every night, at least occasionally.
Why wait until then? When you prune a rose it signals the plant that damage has been done and it immediately starts trying to recover the lost limbs. Remember plants are not trying to please us; they have only one goal–to reproduce themselves. That is the whole purpose of the flower. So when the canes are pruned back the plant realizes it has fewer possibilities for producing roses (reproducing) next year and it works to remedy that. If it is still warm outside to produce the GDUs (growing degree units) needed for growth it will produce more canes. These canes are very young and very tender. Read that as very susceptible to frost and freezes.
Mechanically, what happens when your canes freeze is this. Remember field trips in school? We were always told to bring a sack lunch and a soda pop with us. At my house that usually meant my mom would take a can of Dr. Pepper, put it in the freezer for a while, then remove it and wrap it in aluminum foil so it would be cold for my lunch. However, there were times we forgot the can in the freezer. The next time we opened the freezer door there would be frozen droplet of Dr. Pepper everywhere. Even though most things contract as they get colder, liquids actually expand. The expanding liquid inside the can stretched the can as far as it would allow, but eventually it would stress and burst. This is the same thing that happens to these new canes on your roses. Inside each cane are plant cells that have some ability to stretch and expand, but it is limited. As the moisture freezes and expands, eventually the cells rupture; that cell is now dead. If that happens to enough cells, that section of the plant will die. In extreme cases, the skin on the newly formed cane itself will rupture and create a small fissure or crack in the skin.
So what damage does all of this cause? Well, if just a few cell die, not much. the plant is resilient and will likely overcome the mild damage. If enough cells die, though, it can kill the cane. If a crack is created in the skin, insects will see this as a weakness in the defenses of the plant. Believe it or not, many insects vision see things in infrared. Because of that, this injury shows up like a beacon to beetles and other opportunistic feeders from hundreds of feet away. It’s like a glowing neon sign at a diner that says “OPEN!” This opening not only serves as a dinner bell for insects it is also a perfect breeding ground for bacteria. So, the light freeze damage in the fall, suddenly becomes a point of entry for disease, bacteria, fungus, or insects that may kill your plant completely next season.
Additionally, all of the energy spent producing these new canes that will invariably die is energy lost to the plant next spring. It is best to wait until the nights are cool enough so that the energy expended on new growth can be utilized in the spring when those canes will have opportunity to produce the rose you desire.
So how should you prune, and when? Again, wait until nighttime temperatures are in the 40′s. Then prune back every cane to a three-leaf axil. You should always use sharp shears and cut on a 45-degree angle about 1/4 inch above your selected axil. (See Diagram to the right). Monty also tell me to moisten your finger and rub it in the dirt after you cut the cane, then rub the dirt into the cut on the plant. This, he tells me, will cover up the wound and keep the insects from finding it as readily.
Keep checking this post regularly as we will soon have more conversations and videos from Monty himself to give you the rose-growing tips of a champion rosarian. Additionally, we provide answers to your questions each week in our “Ask Monty’s” section so keep posting your questions to the blog or send us an e-mail. And when you write, or e-mail, make sure to include pictures of your garden. We always like to see what others are doing and learn about the successes they are having with Monty’s Plant Food.