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when and how far to prune knock-outs

10 years ago

I am new owner to a home with about 8 knock-out rose bushes. They were unpruned last spring-summer and ended up huge...at least 4-5x4 feet. This past late fall I pruned them to about 2 feet tall which is what they are now.

1) Should I prune them shorter?
2) When should I do it? I am in NE Ohio. A friend told me I should not prune them now (headed to 50 degrees today) because it'll encourage growth which will be killed when it freezes hard again, which it certainly will.

Thanks for your advice,
Bonnie

Comments (6)

boncrow66
10 years ago
I have to tell you that my name is Bonnie Jean too! I don't see many people with the name Bonnie much less the same middle name. I live in Texas and I have several knockouts and I have found it really doesn't matter how far you cut them back they always do well. I usually prune mine in February but we have a milder winter here in SE Tx. I camehome one day and my hubbie had pruned my knock outs so short I felt sure they wouldn't survive but they did and looked great when they grew. Knockouts are very hardy so I think you will be safe in anything you do to them. I would think if you pruned them in November that that should be good for this spring. But who knows, live and learn. Good luck!

Bonnie
Bonnie
Original Author
10 years ago
Wow, I have never met another Bonnie Jean!

I have heard the same thing about cutting them back hard, that it doesn't bother them.

Still left with the question of when.

Thanks for your input.
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I haven't had roses long either, but I think it is fairly easy to see where to prune in the spring. Wait to do it after your last frost which should be around March or April. It is a signal for your rose to start growing again so wait until you are sure it is safe. Now, when you look at your rose this spring you will see brown ends on the canes. That is dead wood, and you will cut all of that out. Make your first cut just below the brown wood into the green part of the cane. If you don't see any green cane then prune down to the soil. If the green cane is all white inside like an apple, it is good wood. If the inside is brown then you need to prune further down. Watch for dark areas on the green canes. That is canker and you need to prune below any canker you see. Once you have finished pruning seal all the cuts with something. I use regular white glue, but you can use carpenter's glue or nail polish. That will keep out borers which would otherwise lay their eggs inside the cut end of the cane. Feel free to stop by the rose forum for more advice. I post there quite often and everyone is very helpful.
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I am actually trying to get a handle on how low to prune if I want my knockouts to eventually be about 4 fet tall. Can anyone help? I just cut them back to about three feet but my hunch is that from here they'll go crazy. Two feet seems so smlll compared to where I am starting from. This will be their third year. Last summer they got to be about 5 feet and that is larger than what I want right now. The first year they were in they grew pretty slowly and last year I pruned in early April to about 2 feet and they grew to about 5 feet. Should i go back to 2 feet if i want an outcome of 4 or should I go to three feet and then cut back in the summer if they are larger than I want?
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You probably didn't kill them, but you didn't do them any favors,either. Somehow, some folks in Tennessee have decided that roses are the same plants as other shrubs. This leads to some who severe prune as early as late September and again in November. This sort of thing takes strength away from the plants. Roses don't want to go dormant here. If you cut them in fall, they'll put out new growth in two to four weeks, even though it's not yet winter. That growth will probably be killed in late December, and that earlier cutting will have taken away the stored 'strength' that would go to regrow the plant in spring. I've watched some Knockout that have been pruned three times this fall. I don't know what the heck the grounds crew thinks they are doing, much less why. What you should have done (in my opinion) was go through and snip off broken canes. Then in late December go in and prune back for height, depending on how high you want them to be next year. The winter killed new growth that you are going to get, you'll see it contorted and blackened, you can snip it off in winter as well.
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nicholas_delo 7a
10 years ago
In NJ I prune mine when the forsythia starts blooming (I think a lot of others do the same as this is a good indication spring has officially begun).

Other than that, you can just wait until you no longer have to fear frost or ice damage, so more or less when the temps at night reliably stay above freezing.
diane_nj 6b/7a
10 years ago
I think down to 2' is enough. Once last frost date has past, you'll want to check to see if what is left is still green to the tips. Of not, you can prune off that bit, or just leave it. Knock Out will send out new growth to cover.

Like nicholas.delo, I prune in late winter/early spring, meaning late March/early April, when the forsythia blooms. I don't prune in the fall.

This post was edited by diane_nj on Mon, Mar 17, 14 at 9:42
jim1961 / Central Pennsylvania / Zone 6
10 years ago
I usually prune late March early April here...
This year is much colder than usual so who knows?
When the forsythia bloom in your area would be a good time to prune.
Bonnie
Original Author
10 years ago
Thanks everyone. I'll watch out for the forsythia, but will keep the overall weather in mind. I'll look out for when when it's starting to send new growth out. My crocus is starting to bloom and for sure there is plenty of winter left.

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