Tips for Pruning Knock-Out Roses and Other Shrub Roses

Great Flowers That Need Only Occasional Attention

Knock Out Rose
Getty Images/Garden Photo World/Georgianna Lane

Among the family or landscape roses, the shrub roses occupy a unique niche apart from the more temperamental hybrid tea roses, floribundas, and grandifloras. As a class, shrub roses tend to be less showy plants that often resemble the wild parent species in their growth habit. More often than not, there is one main flower production period during the growing year, with sometimes a second smaller flush of blooms in the early fall. But while the flowers are less dramatic, shrub roses make up for this by being extremely hardy and far easier to care for than the sensitive teas and other hybrids. Pruning tends to be a much easier process than with hybrid roses, although the exact methods for pruning depend on what type of shrub rose you are dealing with.

Large Upright vs. Low Ground Cover Shrub Roses

There are many ways to categorize shrub roses, but the most basic distinction is between these with an upright, bushy habit, and low-growing shrub roses .

Larger upright shrub roses, including some considered ramblers, are often used to make large, bold statements in a garden, due to both their blooms and sprawling architecture. Similar to upright shrub roses are old-fashioned roses of the type that were popular before the rise of the hybrid tea rose. Since these old-fashioned roses require much the same type of care as shrub roses, they are usually considered together when talking about pruning. Large shrub rose bushes are somewhat wild and ill-behaved when compared to the narrow upright hybrid tea roses, or even the low mounding habit of the floribundas (although floribundas must be taught their obedience through pruning). Many shrub roses also bloom only once a year instead of the “from summer to frost” period of many popular modern roses.

Many low-growing shrub roses, including a special class of selectively bred roses known as the Knock-Outs, are used as ground covers in sunny areas because of their toughness and hands-off maintenance requirements.

While there are some general rules for pruning all shrub roses, there are also specific tips for pruning specific types of shrub roses.

General Pruning Tips for All Shrub Roses

If you do nothing else, two rules of thumb will let any shrub rose thrive fairly well:

  • Deadhead them. Whether your shrub rose blooms once a year over a short period in late spring or early summer, or blooms repeatedly, it will likely benefit from deadheading, which will promote a longer bloom period and may even prompt a second bloom period. Some types, like the Knock-Outs, do self-deadhead, dropping their spent flowers automatically. Roses that never produce hips, or that produce tiny or mangled hips, do not need to be dead-headed to increase blooms. Late in the blooming season, you may want to stop deadheading and let the hips ripen for an autumn show or to provide food for birds.
  • Allow large shrubs to get large. Many shrub roses bloom on shoots from old wood, so you cannot cut back old wood in spring without sacrificing blooms. These plants should be tamed little by little—trim out just a few entire canes in spring, then perform whatever minimal pruning is needed to maintain some shape and tidiness, both in-season and during the dormancy period. However, don’t expect a large shrub rose to ever look completely tidy.

    Pruning Tips by Type

    Lee Reich, Author of The Pruning Book, breaks shrub roses and old-fashioned roses down into three classes based on how vigorously they grow. If your rose happens to closely fit one of the types described, you are in luck. If your rose doesn't exactly match one these types, then match yours to whatever description comes closest. A rose that blooms mostly from old structure should be placed in Group 1. Roses that produce some blooms from new wood but mostly from old wood should be placed in Group 2. Roses that put up a lot of new growth from the ground and bloom on both old and new wood should be considered Group 3.

    • Group 1 (few new shoots, flowers produced on old stems): Prune lightly in spring. Examples include Gallica roses, Father Hugo’s rose, musk rose, and Scotch or Burnet rose.
    • Group 2 (many new shoots from the ground, flowers produced on old stems): In spring, cut out the oldest one-third the canes, and reduce the length of any remaining long or droopy canes that are too long and droopy. Examples include Burgundy rose, cabbage (centifolia) rose, Rosa x alba, Damask rose, rugosa rose, and once-blooming modern shrub roses.
    • Group 3 (many new shoots from the ground, flowers produced on both old and new stems): Prune hard to near ground in spring. Examples include bourbon rose, China rose, and continuous-blooming modern shrub roses—the Knock Out family fits here.

    The Knock Out® Roses

    The Knock Out group of roses occupies a special niche of shrub roses that incorporates some of the features usually found in hybrid roses. Introduced in 2000 by Wisconsin breeder William Radner, the Knock Out roses bloom repeatedly every 5 to 6 weeks through 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 are renowned for being more resistant to diseases than most roses.

    The rules for pruning Knock Out roses:

    • Always prune in early spring, when new shoots are beginning to form on the canes.
    • Prune to about one-third of the desired final size. Knock Out roses typically triple in size after pruning.
    • Don't deadhead. Knock Out roses are said to "self-clean," and deadheading really does nothing to improve blooming.
    • Remove dead or damaged wood when you see it.
    • Every two or three years, remove one-third of old growth to rejuvenate the shrub.