By pruning your Knock Out Roses, your strengthening the Knock Out Rose to hold all of the growth throughout the year. If you don't prune your roses, they may become too top heavy. Also, pruning in early spring will make your Knock Out Roses full of blooms!
The first pruning is done in late January. At that time, Knock Out roses are cut back by about one-half their height or more, but no shorter than 2 feet from the ground. This prepares the bushes for the outstanding spring/early summer bloom period. The bushes are cut back again at the end of August or early September.
Use a good pair of hand pruners to shorten small branches a half-inch thick or less and loppers for thicker ones. Cut back to a leaf or an outward-facing bud. Remove dead, crowded, or crossing branches to open up the plant's center. Cut back aggressively if you want, but not down to the graft union.
If you don't prune your plant often enough, it won't produce as much new growth. If this is the case, the plant will focus its energy on the existing canes instead. Eventually, this results in a reduction in flowers to the point where you might have none at all.
A general recommendation for the late-winter or early spring pruning is to reduce the height of the bushes by about one-half to one-third. You may do this even if the shrubs are sending out new growth. If the winter is really mild, they may even be producing some flowers, but you still need to prune.
Don't worry about cutting back too much. Roses are extremely strong and will grow back even if you cut all of the stems right back to the base.
Prune to about one-third of the desired final size. Knock Out roses typically triple in size after pruning. Remove dead or damaged wood when you see it. Every two or three years, remove one-third of old growth to rejuvenate the shrub.
Deadheading is the act of cutting off old blooms to encourage new ones. While roses will certainly bloom again if you don't deadhead, it is true they will rebloom quicker if you do. I generally just snap the the old blooms off when they are finished or do a bit of grooming and re-shape the bush when I'm deadheading.
When weather conditions are ideal, Knockout roses can become infected with powdery mildew, rust and even some black spot. More trouble is rose rosette, a new virus disease spread by a small eriophyid mite. It can turn healthy roses into monsters of contorted, crinkled, red stems and leaves.
Rose plant is leggy or gangly, or is not producing blooms is usually because the rose is not getting enough sun. Most roses need a minimum of 6 hours of direct sunlight a day.
We've found that pruning just above an outward-facing bud will promote a wider, bushier rose bush. Knock Out Roses can be pruned lightly throughout the active growth season. Deadheading spent blooms or clusters will encourage quicker formation of new buds and rebloom.
Blooming and Fertilizing
Knock Out® Roses will repeat-bloom from spring to frost regardless of deadheading. Deadheading does offer a cleaner, tidier look. Often people choose to deadhead to remove the faded blooms.
However, with the right care, they can live for much longer – up to 10 years or possibly longer. And how long do double knockout roses live? You can expect them to last 3 – 5 years with little care. But potentially they can last decades with proper care and attention.
Most roses need pruning in early September to look their best this fall. September means it's time to turn off the water sprinklers, plant cool-season fall vegetables, and prune your roses for a showy fall bloom. Mark it on your calendar. Prune roses around Valentine's Day and Labor Day each year.
If it's still leggy and sparse next year, it may be a poor variety, or it may be a growing in too much shade. Dig up your rose in either case and plant a new rose in a different position. Opt for a bare root rose, because these are cheaper and easier to establish.
Answer: The yellow leaves are likely the result of black spot disease. Knock Out roses, in general, are quite resistant (not immune) to black spot disease. During wet weather conditions, however, even resistant plants can be attacked to some degree. That's what's happening now to your Knock Out roses.
Watering Requirements
They prefer deep watering less frequently. When watering knockout roses, make sure to water at the roots of the plant, not on the leaves this will help to prevent fungal growth. It also helps if you mulch around your plants to help keep the moisture in.
Pruning is done once the plants are established, usually after the second year. The difference between the two is that the annual pruning is a more drastic removal of canes while deadheading removes old rose blossoms any time in the growing season.
You don't have to invest a whole lot of time to have bushier knockout roses either, usually just an annual pruning that removes dead or diseased branches and reduces height, if that is an issue. Knockout roses bloom on new growth, not old growth.
These roses grow best in full sun, at least six hours daily. The more sun it receives, it will experience more frequent blooms and be showier. Avoid diseases, like powdery mildew, by providing plants with morning sun and filtered or partial afternoon shade.
Simply keep the roses at the height, and in the shape, you prefer. When you cut back flowering stems, leave 2 or 3 buds on the summer growth. In the cold season, prune English roses by 1/3 to 2/3 of their height. Almost all roses will quickly grow back and recover if you make any mistakes.
Keep them happy, down to four to six canes. We once trimmed back an old, sad bush to three canes and watched it take off. Remember to seal cuts with a protective paste to prevent disease and cane borer problems. After pruning, give your roses a thorough watering ahead of fertilizing.