[TIPS] How and When to Prune Knock Out Roses


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How and When to Prune Knock Out Roses

Knock Out roses are some of the easiest, most rewarding roses to grow! Our yard has 12 fuscia and light pink Knock Out rose bushes. The joy of Knock Outs is their constant blooms from spring until fall.

How and When to Prune Knock Out Roses

Surprisingly, these rose bushes can grow to be quite large if not maintained. Neglecting them is easy since they require little upkeep and are nearly impossible to kill. I’ve neglected a few of mine to the point of needing some serious pruning. Now is the time to prune roses, so let’s take a look at a few tips on How and When to Prune Knock Out Roses.

When to Prune Knock Out Roses

The beauty of Knock Out roses is that they can be pruned nearly any time without sacrificing beautiful blooms. Here in the south, we can expect the first flush of blooms around Mother’s Day in early May. This will be the largest flush of blooms. Then the plant will enter a resting phase and then burst with repeat blooms every few weeks. Maintainence pruning can be done during the resting phase. It is also a good time to cut off withered blooms, but not necessary.

Heavy pruning though should be done in late February in warm, southern climates or in March for the moderate to cool climates. The only time I do not recommend pruning is in the fall. It could trigger new growth that will not have time to harden before winter. One exception is if you live in the deep south then pruning any time of the year is acceptable. 

Recommended Pruning Tools

As a brand ambassador for Troy-Bilt, I have the opportunity to try and review a multitude of lawn and garden tools. Listed below are 3 of my favorite and most used pruning tools. (Amazon affliate links provided for your shopping convenience)

  • Leather Gardening Gloves
  • Bypass Pruner
  • Telescoping Bypass Lopper
  • Cordless Hedge Trimmer
How and When to Prune Knock Out Roses

When trimming roses for floral arrangements or controlling overall shape, I really love my Troy-Bilt Bypass Pruners. They are very sharp, cut through rose stems like butter and fit nicely in my hand.

For woody rose stems over 1/2 inch thick, I recommend using a telescoping bypass lopper. This particular lopper has adjustable telescoping handles, allowing you to easily prune thick, thorny branches without having to reach your hands inside the bush.

This recommendation might surprise you but hedge trimmers can be used on Knock Out rose bushes. We have several Knock Out’s grouped together to form a hedge row. Maintaining and shaping a rose hedge is easy when using this cordless hedge trimmer.

How to Prune Knock Out Roses

Use a clean and sanitized hand pruner for stems less than 1/2″ or a lopper for stems over 1/2″ inch. Cut the stems back to a 5-leaf grouping or an outward-facing bud (if pruning during the growing season). Remove and discard any dead, crowded, crossed or rubbing branches. The goal is to open up the plant’s center and eliminate unnecessary suckers or random shoots. Cut the rose bush back by 1/3 to 1/2 the size. With severe heavy pruning, the plant can be cut down to 18″-36″ depending on how large the rosh bush was.

How and When to Prune Knock Out Roses

Tip: Wipe off the cutting blades of the pruner with antibacterial wipes before moving to a different rose bush. 

I severely cut that 9 foot tall bush back to about 30″ high. New growth has appeared within just one week since pruning.

Start fertilizing with a quality, slow release rose fertilizer in April or at the first sign of significant new growth. In just a couple months the rose hedge will be bursting with blooms look even better than this!

Tips for Pruning Knock Out Roses

The Knock Out group of shrub roses blooms repeatedly every five to six weeks throughout the growing season. There are varieties with both single and double flowers. The plants typically grow no more than 3 or 4 feet tall with a similar spread, and they tend to be more resistant to diseases than most roses.

The general rules for pruning Knock Out roses include:

  • Always prune in early spring when new shoots are beginning to form on the canes.
  • Prune to about a third of the desired final size. Knock Out roses typically triple in size after pruning.
  • Remove dead or damaged wood when you see it.
  • Every two or three years, remove a third of old growth to rejuvenate the shrub.

Do I prune Knockout Roses in Fall or Spring?

This is a good question, and you’ll find gardeners that prefer one season over the other. I’ve always pruned my Knockout Roses in the Fall — however — this year I’m pruning them in the Spring.

In fact, I did prune 3 of the 9 rose bushes last Fall, and the rest of them I pruned recently now that it’s Springtime. I’ll keep you posted on any differences I notice between pruning in Fall versus pruning in Spring.

Prune your Knockout Roses in the Spring when you begin to see buds on the shrubs.

How and When to Prune Knock Out Roses

How much do I cut back the Knockout Roses when pruning?

Height can be confusing, especially if you’re about to prune rose bushes that are tall. Just remember: how much to prune is entirely up to you.

You can cut down by either:

  • 1/3
  • 1/2
  • 2/3
  • down to 12 inches (This is called a rejuvenation pruning.)

Knockout Roses can almost double in size during a season, so if you have a 4 foot shrub, and prune back to 2 feet, it will easily grow back to four feet.

No worries!

How and what to prune Knockout Roses

I cover this in more detail in my video. In short, here is what you want to do when pruning:

First, go for height, using the above-mentioned guidelines.

How much you want to remove is up to you. I have examples of how far back I pruned my own Knockout Roses this year.

Remove any crossing branches.

If the branches are rubbing together, the outer bark can come off and allow fungal diseases to set in.

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