Pruning Knockout roses

When do I prune my Knockout roses?

 Frances Bonner asked if she should prune her Knockout roses since it was well into November, but they were still blooming prettily.  Lots of people have asked the same question.  Actually, I get a lot of questions about caring for these wonderful plants.

7 foot Knockout
This Knockout rose is planted in a large pot. It was pruned well in March and fed every 2 weeks with liquid fertilizer. Still blooming in mid November.

 There are two main reasons for pruning the roses. The first is to keep them in bounds.  Knockout roses, left uncut, will get really big.  Pruning them will make them bushier and stronger.  The plants flower on new growth. A periodic pruning will give more new growth and therefore a greater abundance of flowers.  So pruning will give you both a stronger, better shaped plant and more flowers.  It’s worth the effort. But the question is when?  Here’s my analysis:

First, I went to the grower and found this picture of hundreds of uncut roses.  This told me something.

Hundreds of Knockout roses waiting to be pruned at the wholesale grower's nursery.  Picture taken mid November.  The grower says it's good work for his crew in January.
Hundreds of Knockout roses waiting to be pruned at the wholesale grower's nursery. Picture taken mid November. The grower says it's good work for his crew in January.

My mother has some magnificent Knockouts in front of her house in Kingsport, Tennessee which are still blooming in November.  I told her to leave them alone except for “deadheading” (taking off the spent flower heads) and to wait until January to prune them.

 There are three reasons for my advice.  One is that sort of “gut” feeling that I get about how to treat plants.  I have developed this over more than thirty years of being a grower and landscaper.  Reason two is because the plants are still pretty, so why bother them?

 The third reason to wait is because it has been a mild winter so far and the plants have probably not had enough time to winterize.  If they are pruned and some warm weather shows up, the lateral buds may be fooled into thinking it is time to grow.  If they start their soft new growth and a freeze comes, the new growth will suffer some damage that will require the plant to form new buds for spring growth.  This is, however, mainly conjecture on my part.  If you have already pruned them, don’t worry.

 When you do get around to cutting back the roses, look for a new growth bud on a healthy stalk and cut just above it.  This will be next year’s growth.  I always try to take off (or at least cut back) the spindly stems that have been shaded through the summer.  I usually cut the plants to about 18 inches from the ground, more or less.

 One thing to remember when the Knockout rose is actively growing and blooming is to cut off the dead flower heads.  This is called “deadheading” and it works with almost all flowers.  If you deadhead the plants, the plants will bloom much more heavily.  This is true of pansies, roses, marigolds, and many more of our beloved flowers.

Ain't it pretty? A rose shining in mid November

 While working on this article, I visited one of my clients, Susan, who showed me that a herd of caterpillars had eaten all of the leaves off her roses in one day.  She said she would like to prune them back but thought it a bit too early. She agreed that new growth may be hurt if they are cut before it gets really cold.  Susan is a knowledgeable gardener.

 What it boils down to is, let the roses bloom as they wish.  Then cut them when you wish.  Everything will be all right.

 And before you work on the roses, remember, get some good gloves.

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