How to Prune KnockOut Roses
KnockOuts® are by far the most popular roses planted today. They bloom from spring to hard frost, are disease-resistant, and require little maintenance. But there may come a time when you want to shape the bush or prune it to keep it in bounds. Here’s how to prune your KnockOuts.
When to prune. Pruning a rose bush causes the plant to grow new stems and leaves at the point of the cut, making the bush fuller and adding more flowering sites. This tender growth takes time to mature before it can withstand cold weather, so don’t prune (any shrubs, not just roses) after August first.
Most industry sources recommend pruning KnockOuts just as buds break in spring, because very low temperatures are unlikely to recur. Some of these same sources say “never in fall and never in winter", but we disagree. Between the first hard freeze in fall and the end of winter is okay, because our mountain winters don’t normally have warm spells that are long enough to spur new growth. And while pruning when the buds are breaking is ideal, additional trimming from spring through the first of August doesn’t seem to harm KnockOuts at all.
How much to prune depends on what you are trying to accomplish. Don’t prune KnockOuts the first year or two, allowing the bush to get established. But after that:
- To keep the plant at a specific height, cut off about a third of the top growth each year.
- To renew a bush that has gotten leggy or out of bounds, cut back to one third of the desired height. It will regrow quickly.
- To maintain a desired shape, you have a couple of options. Shearing with hedge clippers will result in a smooth, formal shape. But I prefer to remove individual stems back to the main trunk, for a more natural look.
- Remove dead and diseased stems at any time during the year. But be patient before doing this in spring. Some stems on my KnockOuts sprout up to a month later than adjacent canes, so I delay this pruning until early May.
- Reconsider deadheading. A couple of my neighbors remove spent blooms on their KnockOuts several times during the growing season, but I have yet to see any evidence that this improves flowering. Not having to deadhead is one of the main reasons KnockOuts are so popular!
When pruning for any reason cut back to healthy tissue. Remove old canes that are thick and woody, and any weak growth on the main canes. Keeping the center of the plant open will improve air circulation and help prevent diseases. Make sure your tools are sharp. Clean cuts heal more quickly than ragged cuts, and don’t provide as much opportunity for pests to enter the plant. Wear long sleeves!
I have a 100 foot row of KnockOuts lining my driveway. They were all supposed to be ‘RedRazz’ (the original red KnockOut.) But a couple of pink KnockOuts snuck their way into the initial planting. Rather than replace these I just let them grow. If someone notices, they become a conversation starter (and I just LOVE to talk about my garden!)
Jim Janke is an Extension Master Gardener Volunteer in Haywood County. For more information call the Haywood County Extension Center at 828-456-3575. © 2013 NC State University.