How to Grow and Care for Knock Out Roses

The absolute best thing about Knock Outs is that they’re easy-care for both beginners and experienced gardeners. “Once established, there’s very little maintenance for these roses, except for an occasional pruning to shape them,” says Heidi Mortensen, rose portfolio manager for Star Roses & Plants.

They’re also more disease-resistant than many roses, partly because they’ve been tested in various climates across the country.

“We trial our roses in 14 gardens across the country for a minimum of seven years,” says Mortensen. “They must showcase a high disease resistance to common issues, such as rust in the West or black spot in the East, in order to be selected for breeding.”

Knock Out Roses

Easy Bee-zy Knock Out Rose

How to Plant and Care for Knock Out Roses

Like all roses, Knock Outs need full sun, which is considered 6 or more hours of direct sunlight per day. They will not bloom well in shade.

Knock Outs are adaptable to many different pH levels from neutral to acidic (though 5.5 to 6.5 pH is ideal). They also adapt to most soil types, though they prefer sandy, loamy, well-draining soil, says Mortensen. (You can get your soil tested, which will include pH levels, through your local state cooperative extension.)

Knock Out Roses

Knock Out Rose

When you’re ready to plant, dig a hole about two to three times as wide as the container, and remove the bush from its container. Gently rub your gloved hand on the root ball to loosen up any roots that were circling around in the pot. Then place the bush in the hole at the same level it was in the container. Backfill the hole, then tamp down, and water well.

Knock Outs are relatively fast-growing because they’re shrubs. But like most perennials and shrubs, these roses “sleep, creep, leap,” meaning they’re somewhat slow-growing in the first season as they establish roots, then grow a little more vigorously the second year, and finally, take off in the third season in the ground. “Once the roots are established, you’ll really see their flower power,” says Mortensen.

How to Water Knock Out Roses

Water deeply about once a week the first year you plant your roses. But don’t just give your shrub a cursory sprinkle. If you’re hand watering, hold the hose on the soil at the shrub’s base and count one-thousand-one, one-thousand-two for a count of five, and repeat this process five times, says Mortensen. This allows the water to soak in, saturate the soil, and get down into the roots, which builds a stronger root system for more blooms.

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If possible, it’s helpful if you can build up a ridge of mulch, rocks, or soil near the base of the plant to create a little “water well” so there’s a contained area for the water to stop and not just run off before it can soak into the ground, says Mortensen.

Knock Out Roses

Orange Glow Knock Out Rose

How to Fertilize Knock Out Roses

All roses are heavy feeders, so you should feed your plants regularly. You don’t need to fertilize the first year because the container will have some fertilizer for the season. But in subsequent years, feed with any rose fertilizer as soon as you start to see three to six inches of new growth, then every 4 to 6 weeks after that, says Mortensen.

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Stop fertilizing one to two months before the first expected frost in your area. “We want the plant to go into dormancy and not push new growth because it needs to concentrate on putting nutrients into the roots to survive winter,” says Mortensen.

Knock Out Roses

Pruning Knock Out roses

How to Prune Knock Out Roses

Pruning is incredibly easy. In the late winter or early spring, just when they’re beginning to show new growth, use a pair of hand pruners or hedge trimmers and cut straight across the shrub. You don’t have to get too fancy or make it too complicated. “Just give them a haircut straight across, pruning them back by about one-third their current size,” says Mortensen.

While you won’t hurt the plant if you forget to prune it, it will look better and push more blooms if you prune it back, says Mortensen. You can cut off any dead or damaged canes any time. In warm climates, pruning also keeps their size more neat and compact.

Should You Deadhead Knock Out Roses?

It’s not entirely necessary because Knock Outs are also chosen for breeding because of their ability to be “self-cleaning,” which means the petals “shatter” and fall off on their own, says Mortensen. But deadheading, or snipping off the spent blooms, will help push larger and more abundant blooms. If you like puttering in the garden, this is a perfect excuse to wander around at a leisurely pace to snip off any faded blooms.

Knock Out Roses

Petite Knock Out Rose

Can You Plant Knock Out Roses in Containers?

Absolutely! Petite Knock Outs were bred so that they grow especially well in containers. Choose a pot that’s about 24 inches across and fill with potting mix. Make sure it has a drain hole because roses absolutely cannot handle muddy feet, says Mortensen.

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You will need to check and water containers more frequently because moisture evaporates more quickly from them. But poke your finger into the soil before you give it a drink; roses like to dry out a bit between waterings. If the soil feels hot and dry, it’s time to water. If it feels damp, you can hold off and check again in a day or so, says Mortensen.

Syl Arena

Coral Knock Out Rose

How Long Do Knock Out Roses Bloom?

“Knock Out roses are recurrent bloomers, meaning they are in bloom continuously from spring to fall,” says Mortensen. “They are not rebloomers, which are roses that have a spring flush and then are quiet and bloom again in the fall.”

Are Knock Out Roses Fragrant?

Early on, Knock Outs were not noted for their fragrance. However, breeding has increased the number of Knock Outs now available over the past 20 years. Some are more fragrant than others, but the two most fragrant are Easy-Bee-zy and Orange Glow.

Knock Out Roses

Knock Out Rose

How to Winterize Knock Out Roses

Because these roses grow on their own root stock (and are not grafted onto a hardier root stock, like older rose varieties), even if your rose gets killed off by a particularly harsh winter, it will come back as the same color and type of Knock Out rose, says Mortensen.

That being said, if you’ve planted in containers in cold climates, you will want to protect the root ball from freezing. Wait until the plant is dormant and has dropped its foliage in late fall or early winter, then place the pot in an unheated garage or basement.

If this isn’t possible, place it up against the house and surround the pot with hay bales to insulate it. The house also offers some radiant heat, says Mortensen.

Most importantly, remember dormant plants still need water, especially if it’s outside on those occasional warm, sunny days. Water it once a month throughout the winter months, says Mortensen.

Common Problems with Knock Out Roses

Generally, Knock Out roses are less susceptible to diseases and pests that affect roses. During harsh summer conditions, you may occasionally see:

Black spot, which may cause black spots and yellowing of leaves with some leaf drop. However, it should not affect the overall health of the plant. Try to water at the base of the plant to prevent fungal diseases such as this one from occurring.
Powdery mildew is a fungal disease that appears as a white substance on foliage. It’s usually more common with mild temperatures and overcast days and resolves in the heat of summer. However, you can use a horticultural oil, if you like. Or you trim off the affected growth, and new growth will appear.
Aphids. Blast them off with a garden hose.
Japanese beetles. The best method—though not fun—is to pick them off one by one and drop them into a bucket of soapy water. They typically aren’t a huge issue, so you usually don’t have to do anything.