The original Knock Out rose (Rosa ‘Radrazz’) bears vibrant hot dark pink roses often referred to as cherry red. This first introduction was simply called ‘Knock Out’ rose and it was aptly named. The flowers are like nothing I’ve ever seen on a garden rose – sultry and more than slightly mad.
This is one of the best disease resistant roses in history. Knock out roses are impeccable in this regard.
Knock Out roses can be controversial with some gardeners, but I think the fuss is overwrought. As a group Knock Out roses are ridiculously healthy, disease resistant (but not immune), bloom all season, and look healthy from spring to fall. Knock Out roses are the model of what future garden roses can be if we all just relax a little and focus on the example they set.
There are now a number of Knock Out rose cultivars on the market, including red, pink, yellow, and a bi-color single form. The original, introduced in 2000, is the one that started it all. It was named an American Rose Society All-America Selection the same year it was introduced.
If you should want the original Knock Out rose in your garden, buy the one designated “Radrazz”.
The original Knock Out rose is often described as a single; this is incorrect. The original Knock Out rose is a loose semi-double form with 7-11 petals.
For the new rose gardeners among us, rose flowers are typically described in three fundamental forms: single (5 petals), semi-double (6-21 petals), and double (22+ petals). To my knowledge there is only one single-flowered Knock Out cultivar: Rainbow.
Some of the old roses may have 50+ petals, giving them that full overblown look so many gardeners love. All of those petals may also lead to balling. Florist roses are double hybrid teas.
In shade or on cloudy days, the original Knock Out rose appears dark red. The sun brings out the vibrant tones.
I think what impresses me most about Knock Out roses is how healthy their foliage looks, even in the dregs of summer. Many people do not realize that roses can go semi-dormant in really hot weather. Knock Out roses just keep pumping out flowers, all on shrubs with healthy, dark green foliage.
Knock Out rose has excellent winter hardiness. It is reliable to zones 5 and warmer. Size is listed as 3′-4′ tall/wide. I would agree with this range, even in the southern U.S., where roses often grow larger than their breeders indicated (or anticipated). When David Austin roses hit the American market years ago, they often doubled in size Mr. Austin’s specifications. Graham Thomas in particular grew into gigantic shrubs close to nine feet high under the right conditions.
Almost every garden source you find will recommend at least six hours of sun a day for Knock Out roses. I disagree (slightly). In the deep south of the United States, three to four hours of afternoon sun is plenty. The Missouri Botanical Garden, a resource I value highly, even recommends ‘sun to partial shade’ for Knock Out roses. While there are roses that can tolerate more shade than others, to read such a recommendation regarding roses is unexpected.
I recently photographed a yellow Knock Out rose growing under fairly heavy shade that was healthy, devoid of blackspot, and full of blooms. Considering yellow roses have traditionally been the most disease-ridden of the modern era, I was impressed.