How and When to Prune 'Knock Out' Roses

'Pink Knock Out' rose. Photo: Steve Bender.

One of our faithful readers, Mandi Villa, writes, "I love my 'Knock Out' rose, but it's getting too big. Can I prune it without killing it?" Yes, Mandi, you can prune without killing your rose. In fact, you can do almost anything to a 'Knock Out' rose without killing it short of rocketing it into the sun.

Roses, long a gardener's favorite and our country's National Flower, still suffer from the reputation of being hard to grow. In reality, roses are tough, long-lived, flowering shrubs. No plant is more flexible, more versatile, and more fun than the rose in all its myriad forms. Southern gardeners now have access to a broader selection of easy-care roses than ever. Now widely available through nurseries and mail order are modern selections specifically developed for heavy, repeated bloom and easy care, as well as heirloom favorites that have always been sound landscape performers.

Rose enthusiasts can fill your head with boundless information regarding these beloved plants. But for beginning and weekend gardeners, there's no need to get picky about what class a rose belongs to or when it was introduced. Whether a rose is new or old, its most important feature is how it performs in your garden. Choose the right rose, and you can fill any niche or empty spot in the garden with just about any color and size you desire.

Why You Should Grow a 'Knock Out' Rose

It takes a lot to impress Grumpy. But impressed he is when it comes to the 'Knock Out' rose. This All-America Selections winner might very well be the best landscape rose in existence. Three traits combine to win it high praise throughout the South. First, large clusters of lightly fragrant, cherry red flowers bloom from spring until the first hard frost of fall. Gardeners in the Coastal and Tropical South can expect year-round blooms. Second, it forms a compact, bushy shrub about 3 to 4 feet tall and wide. This makes it ideal for planting in containers, mixing with annuals and perennials in a border, or growing in a sweep as a low, informal hedge. Finally–and this is big–it never needs spraying for black spot. You don't have to drench it in fungicide every 10 days to keep its deep green foliage looking good.

Types of 'Knock Out' Roses

For long-lasting, easy color, plant any 'Knock Out' roses. Low maintenance and disease resistant, they love to bloom. The original 'Knock Out' rose has cherry-red single petals. 'Pink Knock Out' has beautiful pink single petals. There are also double flower forms of both red and pink. 'Blushing Knock Out' offers light pink blooms. The newest of the 'Knock Out' roses is the yellow 'Sunny Knock Out.' 'Rainbow Knock Out' has a range of colors from light pink to yellow to coral with a yellow center. Plant them en masse—they make great informal hedges. They will flower best in a sunny spot (at least six hours a day) with good drainage. There's no need to keep the flowers groomed; they're self-cleaning.

But if you want it to follow the pruning with scores of blooms on a tidy plant, you must follow Grumpy's rules on when, why, and how to do it.

When and Why to Prune 'Knock Out' Roses

'Knock Out' roses (red, pink, double, etc.) bloom on new growth. This means that you can prune it almost anytime you want without ruining the season's bloom. If you prune in early spring, you'll remove some flower buds and delay flowering, but you'll get lots of blooms in a couple of weeks. During the growing season, 'Knock Out' typically explodes in bloom for a few weeks, goes into a resting phase, and then explodes in bloom again. A resting phase is a good time to prune. About the only time not to prune is late summer and early fall, as this might encourage late growth that wouldn't harden off in time for winter. In the North, winter is not a good time to prune, but winter is just fine in the South.

Although 'Knock Out' is marketed as a compact shrub, over time it gets pretty big. A neighbor of mine has a 'Knock Out' hedge that's 6 feet tall. So periodic pruning is necessary to keep it manageable. 'Knock Out' also tends to produce a lot of fruit, called "rose hips," that inhibit future flowering. Trimming these off brings it back into bloom.

How to Prune Your Rose

First, put on some heavy leather gloves. Grumpy only knows of one thing possessing more vicious weapons than the thorns of 'Knock Out' rose.

Now that you have gloves on, let's proceed. 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. That's the knob at the base where the roots and stems meet.

General Guidelines for Rose Pruning

The following pruning practices apply to all roses except certain shrub and species roses. Special instructions for pruning those roses are included later in this section.

Use sharp pruners. Remove wood that is obviously dead and wood that has no healthy growth coming from it, branches that cross through the plant's center and any that rub against larger canes, branches that make the bush appear lopsided, and any old and unproductive canes that strong new ones have replaced during the past season. Cut growth back produced during the previous year, making cuts above outward-facing buds (except for very spreading selections: some cuts to inside buds will promote more height without producing many crossing branches). As a general rule, remove from one-third to no more than one-half the length of the previous season's growth. The ideal result is a V-shaped bush with a relatively open center.

If any suckers (growth produced from rootstock) are present, completely remove them. Dig down to where suckers grow from rootstock and pull them off with a downward motion; that removes growth buds that would have produced additional suckers in subsequent years. Let the wound air-dry before you replace the soil around it.

Be certain you are removing a sucker rather than a new cane growing from the bud union of the budded selection. Usually you can note a distinct difference in foliage size, shape, and color and in the size of thorns on sucker growth. If in doubt, let the presumed sucker grow until you can establish that it is growing from the rootstock, not the budded rose. A sucker's flowers will be different; a flowerless, climbing cane from a bush rose is almost certainly a sucker.

Consider cutting flowers as a form of pruning. Cut off enough stem to support the flower in the vase, but don't deprive the plant of too much foliage; leave a stem with at least two sets of five-leaflet leaves. Prune to an outward-growing bud or to a five-leaflet leaf.

Make Roses Look Good After a Hot Summer

Another reader, Marilyn, asks: "Is there a way to get my 'Knock Out' roses to look good after this hot summer? How and when should I prune them?" Even a 'Knock Out' looks woozy after months of Southern heat. So put on some leather gloves to protect you from its vicious thorns and then use hand pruners to cut the plants back by about one-third. Next, fertilize them according to label directions with Miracle-Gro Water Soluble Rose Plant Food. As soon as the weather cools and you get some rain, your 'Knock Out' roses will live up to their name, sending out fresh foliage and blooming for the rest of fall.

How to Grow Roses

The rose really is undoubtedly the best-loved flower and most widely planted shrub in the South and all other temperate parts of the world. Although mostly deciduous, roses can be evergreen in mild climates. Centuries of hybridizing have brought us the broadest possible range of forms and colors. There are foot-high miniatures, tree-smothering climbers, flowers as tiny as a thumbnail or as large as a salad plate, and all possible variations in between. Red, pink, and white, are the traditional colors, but you'll also find flowers in cream, yellow, orange blends, and bi-colors, as well as magenta, purple, lavender, and even tan and brown.

Despite the delicate appearance of their blooms, roses are often quite resilient plants. Growing them is not difficult, provided you choose types suited to your climate, buy healthy plants, locate and plant them properly, and attend to their basic needs–water, nutrients, pest and disease control, and pruning.

Location. Choose a spot in full sun (light afternoon shade in hottest regions). In partial sun, it produces fewer flowers. An open area with good air circulation helps discourage foliage diseases. Don't plant where roots of trees or other shrubs will compete with rose roots. Prior to planting, dig a hole as deep as the root ball and at least three times as wide. Work in lots of organic matter, such as garden compost, chopped leaves, composted manure, sphagnum peat moss, or ground bark. As you're working up the soil, mix in some slow-release rose fertilizer (available at any local nursery or home center) at the rate recommended on the label.

Drainage. Be sure the soil is reasonably well-drained.

Watering. Regular moisture is essential for good growth and bloom of most popular garden roses. Mulch soil beneath plants to help conserve moisture.

Fertilizing. Repeat-flowering roses do best with repeated feedings throughout the growing season. Once-flowering roses need less fertilizer: feed them once as growth begins and a second time after the blooming stops.

Pruning. As mentioned above. All roses will be more productive and attractive with some pruning. Thin out dead, weak, and old-growth; reduce plant size according to the type of rose and the demands of your climate.

Pest and Disease Control. It may be necessary to thwart various trouble-makers, especially if you are growing modern roses.

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Southern Living is committed to using high-quality, reputable sources to support the facts in our articles. Read our editorial guidelines to learn more about how we fact check our content for accuracy.
  1. American Rose Society. National Floral Emblem.

  2. Missouri Botanical Garden. Rosa 'Radrazz' Knock Out.

  3. University of Florida Institute of Food & Agricultural Sciences. Knock Out Roses.

  4. University of Maryland Extension. Guide to pruning roses.

  5. NC State Extension. Rosa hybridia 'Radrazz' PP #11836.

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