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 1⁄2 inch (1. 3 cm) in diameter, switch to a set of larger loppers. [2] X Research source Disinfect pruners with rubbing alcohol or bleach diluted with water to sterilize them.
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.
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.
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.
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.
The main pruning period for knockout roses is in late winter or early spring, just as the plant prepares for another season of growth. [7] X Research source 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.
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. [9] X Research source
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. [11] X Research source 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.
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. [13] X Research source
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.
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.
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.
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.
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. [18] X Research source Your roses will benefit from getting a little rest before the next growing season.
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.
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.
