The Double Knock Out Rose [Rosa ‘Radtko’] is a further modified version of the hybridized Knock Out Roses first introduced in 2000 by Wisconsin rose breeder, William Radler.
It is prized for its ability to produce a new flush of intense pink or red flowers every few weeks during the bloom time.
Double Knock Out roses look a lot like the classic rose but are much easier to grow and care for. The common name for these shrub roses is – Knock Out – because they are!
Double Knock Out Rose Care
Size & Growth
The Double Knock Out rose is a deciduous shrub and grows up to 4’ feet tall and 4’ feet wide.
It has a dense, bushy growth and flowers excessively from early spring until the first frost appears.
Flowering and Fragrance
As the name suggests, the plant produces fragrant double blooms – the average size of a Double Knock Out rose is approximately equal to two regular-sized roses placed together.
The color of these pretentious flowers ranges from bright pink to cherry red.
Growing against a backdrop of lively green foliage, these pink and red roses look simply incredible.
Light & Temperature
This rose plant is best grown in United States hardiness zones 4 – 10.
Knockouts are extremely heat tolerant to USDA Zone 11.
It survives temperatures down to -25° degrees Fahrenheit (-31° C).
The plant grows in a wide range of climates, but it thrives in partial shade.
Three to four hours of full sun is sufficient to keep the plant in good condition.
Watering and Feeding Knockouts
The Double Knock Out rose requires plenty of water to grow properly. Water it generously every day in the initial growth stage.
The water should be distributed around the plant, extending at least a foot beyond the maximum reach of its branches.
When the plant matures, the watering needs reduce.
Once a week (or twice during dry spells) is more than enough for mature Double Knock Out rose shrubs to thrive.
Remember, overwatering causes the leaves to turn yellow and fall off.
A two to a three-inch-thick layer of organic mulch such as shredded pine bark helps retain the moisture.
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Soil & Transplanting
The Double Knock Out rose is a hardy, drought-tolerant plant and performs well in most soil types.
However, it prefers well-drained soils with a pH of 6 to 6.5.
It is a good practice to fertilize the plant in the early spring season when it begins to grow new leaves.
Give the plant a second dose of rose fertilizer during mid-summer when the bloom cycle begins.
This helps produce healthy and more prosperous double red flowers.
Grooming and Maintenance
The Double Knock Out rose bushes are self-cleaning.
In other words, the Knock Out rose is a no-fuss plant because unlike other rose varieties, it does not require deadheading – the process of picking off dead or fading blooms from the plant.
Matured flowers drop to the ground where it is easy to rake them. However, pruning knockout roses annually is required to keep the shrub in good shape.
Prune the plant in late winter or the beginning of late spring when it’s dormant.
Crossed or interior branches must be trimmed every year whereas old canes need to be pruned after every 2 – 3 years.
How To Propagate Double Knock Out Rose
The Double Knock Out rose is patented and is propagated it through clippings.
If done correctly, a clipping transforms into a new plant in just a couple of weeks, thereby reducing the time taken by young plants to grow.
- Obtain a 6” – 8” inch long clip by cutting the tip of the Double Knock Out rose at a 45-degree angle just where the hip starts to form.
- Remove the leaves and flowers except for the top-most leaves.
- Dip the cutting in a rooting hormone powder before placing it in a pot (leave one-third of the stem above the soil).
- Cover it with a plastic bag and keep outside where it will receive indirect sunlight.
- Spray the soil lightly to keep it moist.
- Once the rose roots, transplant it to the desired location.
- Leave at least 3′ feet of distance between the propagated stem cutting and the nearest plant to provide an ample amount of space for proper growth and air circulation.
- Gardeners recommend planting Double Knock Out in the months between December and February for the best results.
Double Knockout Rose Pest or Diseases
The Double Knock Out rose is resistant to most of the common garden pests and is disease resistant including mildew and black spot disease.
The chances are rare, but sometimes these rose shrubs are attacked by spider mites, scales, aphids or mealybugs.
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These pests feed off the leaves and usually prefer plants with low moisture content.
Therefore, not watering the Double Knock Out rose will make it susceptible to such garden pests and insects.
Double Knockout Uses
The showy blooms and shrub size of the Double Knock Out rose make it the ideal gardening plant for a variety of different purposes.
Grow it all around the garden as an ornamental bush or plant it as low-maintenance hedges in the landscape.
Brighten up the borders with its richly-colored flowers or plant it along the walkways for a captivating look.