Summer Care For 'Knock Out' Rose

They say it's carefree, but it still needs some attention.

Steve Bender
Pink Knock Out Rose Shrub
Photo: Van Chaplin
'Pink Knock Out' Rose

You’ve heard of all the hype about ‘Knock Out’ rose. “It never stops blooming.” “It never needs pruning.” “It never needs spraying.” “It’s the one rose you can plant and forget.” Are all of those things true? Well…………………..

Compared to other roses, ‘Knock Out’ is pretty idiot-proof. It’s tough, grows in almost any well-drained soil in a sunny spot, and doesn’t need spraying for black spot fungus, the universal bane of rose lovers. But a rose you can just plant and forget? Forget about it.

For one thing, if you want to keep it blooming continuously, you need to groom it. This means clipping off the faded flowers. If you leave them, they’ll form rose hips with seeds inside and flowering will slow to a crawl. Grooming ‘Knock Out’ rose every week or so spurs new growth loaded with new rose buds.

Second, ‘Knock Out’ may start out small and compact when you buy it, but it won’t stay that way forever. Unless it dies, it will get bigger and bigger every year. A neighbor of mine has hedge of ‘Knock Out’ rose that’s now pushing six feet tall. If this is too big for the space you have, you’ll need to prune. Fortunately, ‘Knock Out’ blooms on new growth, which means that you can prune it just about any time of year. Be sure to wear leather gloves, though, as it’s one of the most viciously thorny plants you’ll find. You can cut it down to a foot tall if you want. In response, it’ll send out lots of new growth and blooms.

Third, just because ‘Knock Out’ doesn’t need spraying for black spot doesn’t mean you don’t occasionally have to spray for other things. In hot, dry weather, tiny spider mites on the undersides of the leaves may suck out the sap, causing the leaves to look speckled or bronzed. Then you’ll need to spray with horticultural oil or insecticidal soap. Spraying the foliage with a jet of water also works, because spider mites love dry foliage and hate wet foliage.

Another problem that’s common around this time of year is leaves dotted with small holes. They look like someone fired a shotgun at them. The culprit is a sawfly that lays tiny eggs on the undersides of the leaves. The eggs hatch into larvae called rose slugs that chew away at the leaves from the undersides, leaving little “windows” and holes. Spraying the leaf undersides with neem oil will control this. Neem oil also works against another insect pest that likes to eat ‘Knock Out’ rose, the Japanese beetle. Just don’t spray the flowers, as neem is toxic to bees.

Does ‘Knock Out’ need less care than most other roses? Definitely. Will it look good if given absolutely no care? Definitely not. Now you know.