Knock Out Rose (Rosa ‘Knock Out’)

Rose Breeder Bill Radler created the Knock Out rose bush. It was a big hit, too, as it was a 2,000 AARS and smashed the record for sales of a new rose. The Knock Out® rose bush is one of the most popular roses in North America, as it continues to sell very well. Let’s look at how to care for Knock Out roses.

I. Appearance and Characteristics

The Knockout Rose Tree is a variant of the Knockout Rose family, which was first cultivated by rose breeder William Radler in the late 1990s. What sets this variant apart is the growth form: it’s grafted onto a hardy rootstock, which results in a slender trunk topped with a bushy, vibrant bloom display. This tall and stylish appearance has made the Knockout Rose Tree a favored choice for ornamental gardening.

Disease-resistant, the roses are self-cleaning, so no deadheading is needed. The shrubs do require pruning each year for the best bloom production. While not suitable as a cut flower, the rose will add interest to your garden for many months.

II. How to Grow and Care

Sunlight

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.

Temperature and Humidity

Knock Out roses are cold-hardy and heat tolerant. These flowers can withstand temperatures down to 10°F and periods of frost before going dormant. In colder climates, help insulate the plant’s roots by adding a layer of organic mulch, such as straw, near the base. If grown in containers, add a protected wrap around the plant to protect it from frost.

Watering

Younger plants need more consistent watering than established roses when it becomes relatively drought-resistant. Water the roots in the morning to prevent leaves from developing a fungus from wet foliage. Plants will also need more regular watering during the growing season.

Soil

Average soil with a slightly acidic to neutral pH is best for these plants. Add organic compost or mulch to maintain soil conditions, including adding nitrogen as a supplement.

Fertilizing

While most Knock Out roses do not require supplemental fertilizer to thrive, you can give them a boost if the soil quality is poor. The plants should not be fertilized until they are established and have completed one bloom cycle. Fertilize once in the spring by using a fertilizer formulated for roses. Moisten the soil and spread the fertilizer following the label directions.

Pruning

To keep a full-size or miniature Knock Out rose compact and blooming well, it does require pruning. Full-size roses should be cut back once a year in late winter or very early spring to about 12 inches high. After cutting it back, you can expect the rose to triple in size by the end of the season. After the overall pruning, check the plant for small or damaged canes and remove those for stronger growth and airflow between branches.

Propagation

Strictly speaking, propagating a Knock Out rose is illegal. This plant, as well as many other roses and perennials, is patented, and propagating the plant is illegal for 20 years from the date the patent is filed unless you have permission from the patent owner. This includes planting seeds or propagating bushes from cuttings, even just for growing in your own backyard.

Potting and Repotting

Repot Knock Out roses every two to three years as they will outgrow their container. When transplanting roses, select a container with good drainage at least two times larger than the current pot so the plant has room to expand. In the spring, gently remove the rose from the older container and shake off any excess dirt. Add the root ball to a new container filled with fresh potting soil. Plant the rose so the top of the rootball is flush with the top of the soil. Water often while the roots establish, checking the soil daily in extremely hot weather. In colder climates, move roses to a warm location in the winter, so the roots do not freeze.

Overwintering

If you live in an area with harsh winters, add 2–3″ of mulch around the base of the rose or wrap the plant in burlap. A heavy snow cover helps insulate and protect the plant through the winter. In the spring, remove the burlap and trim out any dead or broken canes. Remove any excess mulch.

If you have full-size or miniature Knock Out roses in containers, leave them outside through the first few frosts to help the plant go dormant. Then bring the container inside and store it in a cool, dark area. Check periodically and add just enough water so they don’t dry out completely. Once the threat of frost has passed in the spring, return the containers to their outside location

How to Get to Bloom

If your roses aren’t blooming, they are probably not getting enough sun. Move the plants or prune plants around them so they receive at least 6 hours of sun per day. Yearly pruning will also produce new canes that produce the most blooms.

Pests and Diseases

Common Pests and Plant Diseases

While Knock Out roses were developed to be disease resistant, they can still be affected.

• Black Spot

Black spot can appear on the leaves in humid areas. Watering only at the base of the plant will help improve the situation if black spot appears. If powdery mildew, a fungal disease, appears during cool, humid days, apply horticultural oil to affected areas. It is also a good idea to trim back heavily affected areas.

• Voles, Beetles, and Slugs

Knock Out roses are not deer and pest resistant—voles find the roots tasty. They are also susceptible to Japanese beetles and rose slugs or sawflies. Remove the beetles and rose slug larvae by hand and treat mature rose slugs with insecticides.

Common Problems with Knock Out Roses

If the foliage is turning yellow and dropping, it is most often due to excessively high temperatures or overwatering. Water only at the bottom of the plant and check the soil moisture so you do not leave the plant with wet roots.

III. Types of Knock Out Roses

• Knock Out ‘Radrazz’: The original Knock Out rose is a single cherry red, hot pink bloomer with deep, purplish green foliage.
• Double Knock Out ‘Radtko’: A double cherry red rose developed from the same line as Radrazz that is slightly more winter hardy.
• Blushing Knock Out ‘Radyod’: Light pink single blooms with mossy green with hints of blue foliage.
• Coral Knock Out ‘Radral’: Produces brick orange blooms that fade to coral. A more upright cultivar, it can reach 4.5 feet high and 4.5 feet wide.
• Peachy Knock Out ‘Radgor’: A mounding rose, the blooms are shell pink with a yellow center.
• Pink Double Knock Out ‘Radtkopink’: Bright, bubble gum pink blooms on a plant that tolerates heat well and has superior drought tolerance once established.
• Pink Knock Out ‘Radcon’: Single bright pink blooms on mossy green foliage.
• Rainbow Knock Out ‘Radcor’: Coral-pink blooms with yellow centers, this rose is more compact than others with new foliage appearing as deep burgundy aging to dark green.
• Sunny Knock Out ‘Radsunny’: A more upright rose, it produces bright single yellow flowers with a citrus scent that fade quickly to a pastel cream color.
• White Knock Out ‘Radwhite’: Compact and bushy, the single white blooms are showy against dark matte green foliage.
• Petite Knock Out ‘Meibenbino’: The first miniature Knock Out, the mature size is 18 inches tall and the plant is compact and bushy. Blooms are 1.5 inches in diameter and non-fading fire engine red. The plant is suitable for container or landscape planting.
• Easy Bee-zy Knock Out ‘SRPylwko’: Under limited availability, this yellow single rose will be available in garden centers in 2024. The rose is bushy with a citrusy scent that attracts pollinators and are hardy to Zone 4.
• Orange Glow Knock Out ‘Radslam’: Under limited availability, the vibrant orange rose with hints of yellow and pink will be in garden centers in Spring 2024.

IV. Uses and Benefits

The Knock Out rose tree is a perfect focal or specimen tree in a yard, a mixed bed, or garden. Combining your rose tree with Knock Out Rose shrubs and Drift Roses adds loads of color, endless blooms, and a stunning look. Try planting a single or double Knock Out Rose tree on each side of your front door or entryway for a beautiful welcome home. The Knock Out Rose tree is even gorgeous in containers in front of your home, on your patio or deck. Those with small, urban yards can have the classy tree they want in the shrub size they need.