The Joy of Landscaping

A Gardening Blog

How to Care for Knock Out® Roses

The joy of low maintenances roses! **

I was thinking today about what tasks needed to be done this month with the gardening season around the corner. "Prune the Knockout Roses" is on list. It’s one of the few times of the year that I need to pay some attention to these marvels of horticulture. You see, despite my intense love of garden design, I just don’t like plants that are fussy and need a lot of hand holding. That’s why I stayed away from roses for so long.

Fortunately, Knock Out Roses® (Rosa x “Radyod”) came along and at last, I’ve been able to enjoy roses in my own landscape. While the Blushing color works best in my yard, they come also in pink, red and yellow rose colors.

knockout rose

So what is involved with caring for them? First, I cut them back every March. This should be done in late winter or early spring before they start to bud. In the past I’ve taken off about the top 1/4 to 1/3 of each branch to help keep them from getting too tall when they grow out over the season.

Every spring, all my plants get compost fertilizer, and the roses get fed along with everything else. While they are also fairly drought tolerant, I do water them if we haven’t had rain for a week in the hot summer months. That’s about the extent of the human care they get, and so far, so good.

One thing to watch out for are Japanese Beetles, typically beginning in June. (This is not unique to the Knockouts as the beetles love roses in general.) In my Gardening Club’s garden, we have several Knockout Roses planted next to a Hawthorn and a Crabapple tree, which appeared to be the first attraction for the beetles. However, they quickly found the roses as a new source of food and started attacking them. I spent several weeks laboriously picking them off the plants and dropping them into a bucket of soapy water. While the foliage was pretty eaten up, the beetles did not appear the next year and they recovered nicely.

** Unfortunately, I have discovered, through the miracle of the Internet, that “the bloom may be off the rose” for Knockouts and roses in general. The problem is a disease called “Rose rosette”. While you can find numerous information sources about this disease, here's one to start with.

In short, this virus causes new shoots to be bright red and thick, and the new flowers are deformed. It spreads throughout the plant and kills it. All because this virus got going in the U.S. with the introduction of the invasive multiflora rose, which is its primary host and source. Well, the virus is doing an admirable job killing this invasive, but it also apparently likes other types of roses as well. The only saving grace in this story is that the disease seems confined to roses.

What to do? Keep a sharp eye out for the symptoms noted above on your Knockouts (or any of your other roses). Plants are typically affected in the Spring and show symptoms in mid Summer. If you think the plant has the disease, remove the whole shrub and do not compost it. (Also, disinfect any tools you use to get the shrub out.) If you don't remove it, it can pass the problem, through the wind, to any other roses in your yard and beyond.

If you haven’t seen any symptoms yet, for the yearly late winter pruning, cut it back by 1/2 to minimize possible overwintering eriophyd mites and their eggs that help the virus spread. In June and July, try applying insecticidal soap or horticultural oil on a weekly basis to help kill any mites that may be on the plant, although it's unclear whether this will stop the virus if it's already in your neighborhood.

So the low maintenance rose has now become more maintenance. For now, I’ll accept the extra duties and hope that a remedy will be found before my roses become victims.