A sort of catch-all class of roses is the shrubs, which include the extremely popular Knock Out line of roses. Many low shrub roses, including the Knock Outs, are used largely as low ground covers in sunny areas because of their toughness and lack of need for maintenance, including pruning.
Larger shrub roses, which in growing habit resemble their wild species parents, are used as large, bold statements in a garden with both their blooms and sprawling architecture.
Some of these are old-fashioned roses, the roses that were popular before the rise of the hybrid tea rose, and since these old-fashioned types are cared for much like shrub roses, they are usually grouped together when talking about pruning.
Large shrub rose bushes are not well-behaved like the narrow upright hybrid teas or even the low mounds of floribundas (which even themselves are not really “well behaved” until you help them behave with your pruners). Some shrub roses also bloom only once a year instead of the “from summer to frost” period of many popular modern roses.
In short, shrub roses vary a lot, but they can be categorized and pruned strategically.
The Knock Out® Roses
The Knock Out group of roses is a trademark named group of seven varieties including double bloom and single bloom types. They need very little care, so little that it can be easily summed up here.
- Spring pruning: a hard cut back to about a foot high. This is not necessary, but it’s best practice. The heavy cut now increases summer blooming and maintains the size. Do this after the last winter hard frost.
- Don't deadhead. Knock Out claims to "self-clean." It also allegedly produces small rose hips, but what is for sure is that the plant blooms heavily and continuously without deadheading so it’s hard to imagine that the very tedious task of deadheading will improve anything.
- Dead, diseased, and damaged wood. Remove as usual, but Knock Out is virtually disease-free.
Pruning Tips for Specific Popular Shrub Roses
Author Lee Reich of The Pruning Book breaks shrub and old-fashioned roses down into three classes based on how vigorously they grow. If your rose happens to be one one of the ones on this list you are in luck -- you can find the recommended pruning approach you should take below.
If yours is not on the list, try to fit your type to what is described. Roses that bloom mostly from an old structure are in Group 1; roses that put up a lot of new growth from the ground and all over the plant and bloom on all growth in 3. Roses with some new growth but still blooming mostly on old wood are in 2.
Group 1, few new shoots, flower 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 ground, flower on old stems. In spring, cut out oldest 1/3 or so of canes, and reduce length of remaining canes that are too long and droopy. Examples include Burgundy rose, moss rose, cabbage (centifolia) rose, Rosa x alba, Damask rose, rugosa rose, and once-blooming modern shrub roses.
Group 3, many new shoots from ground, flower on all 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.
Pruning Tips for All Shrub Roses
Deadhead them. Whether your shrub rose blooms "once," meaning over a short period in late spring or early summer, or blooms continuously until frost, it will likely benefit from deadheading. Some types, like Knock Out, do self-deadhead. If you never see rose hips appear or they seem tiny and mangled, you don’t need to deadhead to increase blooms.
Allow large shrubs to get large. Many shrub roses bloom on shoots from old wood, and so cannot have old wood cut back hard in spring without sacrifice of blooms. These plants should be tamed little by little -- just a few canes cut out in spring, and whatever minimal pruning needed in-season and in dormancy to maintain some size and tidiness (but don’t expect a large shrub rose to ever look truly "tidy").
- Reich, Lee. The Pruning Book: Completely Revised and Updated. Taunton Press, 2010.
- Royal Horticultural Society. Rose pruning: shrub roses.