How to Prune Knockout Roses

Pruning Roses Correctly

Grab a pair of sharp bypass pruners. Bypass pruners cut like scissors, making them preferable to anvil-type pruners, which have a tendency to crush the stems as they cut. Nice, clean cuts are essential to maintaining the health of the plant. If you don’t have a pair of pruners handy, you could also use full-sized hedge clippers or trimmers. Whatever tool you use should be nice and sharp and able to make clean cuts. When you need to cut canes larger than about ⁄2 inch (1.3 cm) in diameter, switch to a set of larger loppers. Disinfect pruners with rubbing alcohol or bleach diluted with water to sterilize them.

Wear gloves to protect your hands and arms. In order to prune your knockout roses safely and effectively, you’ll need to pull on a pair of rugged elbow-length gardening gloves. Your gloves should be thick enough to safeguard your skin from any thorns growing on the bushes. Don’t attempt to prune your knockout roses without some kind of protective covering—a pair of standard wrist-length gardening gloves is better than nothing.

Disinfect your pruners before you get started. While you’re pruning your roses, stop periodically to dip them into a container filled with cleaning solution. Any all-purpose household cleaner will do the trick. Making sure your cutting blades are properly sanitized lowers your chances of accidentally spreading disease from one plant to another. Get in the habit of disinfecting your pruners regularly, whether you’re trimming a little or a lot. Alternatively, you can use a solution made up of 70% rubbing alcohol diluted in water.

Cut the canes at a 45-degree angle. Make your cuts roughly ⁄4 inch (0.64 cm) above an outward facing bud, with the slant pointing away from the bud. This helps promote new growths to grow outward rather than inward. This technique should be used regardless of the time of year or size of the growth you’re pruning. Angled cuts help water run off the stem and reduces the chance of fungal rot. Cutting too close to the bud could shock it, while cutting too far away might leave too much old growth behind, forcing the plant to direct valuable resources to canes that are no longer able to produce new buds.

Performing Major Pruning in Early Spring

Wait until the second or third season of growth to cut back your roses. By holding off until your roses have neared their full size, you can ensure that they’ll be able to withstand having whole sections removed. A mature knockout rose should be about 4 feet (1.2 m) tall by 4 feet (1.2 m) wide before you begin hacking at it. A fully-grown knockout rose will require the most pruning around mid-February to early March. Young roses, by contrast, only need to be touched up throughout the growing period to remove dead or dying growth. Knockout roses can often go as long as 2-3 years between major prunings, depending on how rapidly they grow and how big or small you like to keep your plant.

Prune your roses as soon as the buds break dormancy. Look for small buds to begin forming along the stems of the plant. If the existing buds have swelled up but no new growth has appeared, it means the roses are ready to prune. The main pruning period for knockout roses is in late winter or early spring, just as the plant prepares for another season of growth. You can still prune your roses even if new growth has already begun. Buds might start forming early if the winter was especially mild. In this case, snip the growth back to the first dormant bud.

Start by cutting away overlapping canes. Clip one or both canes as needed to get the plant’s interior structure growing straight and vertical. Creating some separation between the canes prevents them from rubbing against one other, making the plant look neater and promoting stronger, more lasting growth. By reducing the density of your rose bushes early in the season, you can make sure they continue putting out neat, attractive growth all year long. Thinning out overlapping canes and stems also promotes better air circulation through your rose bushes, making them less vulnerable to fungal diseases.

Remove one-third to one-half of the plant’s overall size. You can cut healthy shoots back considerably without worrying about harming the plant. Doing so will prevent your roses from putting too much energy into maintaining an overabundance of foliage. As a result, it will produce more flowers. Keep in mind that your knockout roses will grow vigorously after being pruned. As a general rule, you’ll want to cut them 1–2 feet (0.30–0.61 m) shorter than you would ultimately like them to end up. Be careful not to get too overzealous with your pruning. Trimming more than half of the healthy, mature canes could cause the plant to struggle to regrow lost foliage, stunting its growth.

Trim your bushes to the desired height and width. Maintain the appearance of your knockout roses by giving them a gently rounded, dome-like shape. Be sure to snip any stems or offshoots that extend far enough beyond the foliage on the outer edges of the bush to stand out. To improve air circulation and control the spread of diseases in warmer weather, try trimming your bushes into a rough ‘V’ shape, leaving them open in the middle.

Maintaining Your Roses During Late Spring and Summer

Do some corrective pruning throughout the peak growing season. Shaping up your rose bushes sporadically as they fill out will encourage them to put more of their resources toward producing beautiful new buds. With a little attention here and there, you’ll begin to see more dramatic flower production by the time the days start getting shorter. Avoid heavy prunings during the heat of the summer. Your roses will already be somewhat stressed due to the heat, so losing too much healthy growth only weakens them further.

Remove damaged and diseased wood. Any sections of the plant showing signs of disease should be dealt with immediately to prevent the condition from spreading. Similarly, old, brittle wood invites harmful pests, fungi, and bacteria to attack the plant, and should also be cut back as soon as possible. Throughout the growing season, the primary purpose of pruning is to keep your roses healthy and active. This can be achieved by removing any unhealthy-looking parts of the plant that could become an issue if left alone.

Deadhead dead and dying blooms to extend the bloom season. Deadheading is the practice of snipping off spent or failing flowers in order to make room for new ones. Snip the stem down to first group of five leaflets below the flower cluster. In a few short weeks, another round of blooms will appear in their place. In most cases, you’ll be making your cuts approximately 6–8 inches (15–20 cm) below the flowers themselves. During extreme heat, only cut back to the first set of leaves rather than going further down the stem. Deadheading is essential for improving both the health and aesthetic quality of your knockout roses.

Aim for a uniform appearance. If a few fast-growing shoots exceed the length of the surrounding shoots, trim the longer sections to restore the plant to an even length. Repeat this process on all visible sides of the bush. Otherwise, it can quickly overtake its surroundings and begin looking unruly. In addition to vertical growth, new growth will also expand outward and below the plant in the spring and summer. This "leggy" undergrowth should also be kept short.

Trimming Your Roses Before Winter

Prune 1 final time if desired before the first frost of the year. Ideally, you should aim to have your pruning done by the end of summer or the first couple weeks of fall, when the weather is still warm. Once it gets cold, new growth will begin to taper off as the plant prepares to enter dormancy. Stop pruning your knockout roses in early fall at the latest. Any new growth they put out after this time may not harden off in time for winter. Your roses will benefit from getting a little rest before the next growing season.

Clear away dead wood. Just like you did in the summer, inspect your knockout roses carefully once more to identify and cull weak, sick, or dying canes. Otherwise, disease could spread throughout the bush unchecked, kill it off completely by the time winter sets in. At this point, it’s advisable to remove as little of the plant’s overall size as necessary. Avoid disturbing younger canes. You don’t want to accidentally stimulate new growth that will just die off and weaken the plant.

Reduce the overall height of your rose bushes. Just before your roses retire for the season, you can trim up to one-third off their total height. Focus on excess growth that doesn’t contribute to the general shape of the bush. If there are any long, non-flowering stems sticking out from the top or sides, be sure to see to these as well. If your roses just barely managed to reach their ideal height during the peak growing season, a little light corrective pruning will be best. Fall pruning is not a major ordeal, and many gardeners even choose to skip it altogether.