The Knock-Out rose bush is one of the most popular roses in North America for good reason. It's a prolific grower and needs little in the way of maintenance. It is very disease resistant and will continue to produce cheery blooms without the need to deadhead them. For gardeners who like roses in their flower gardens, but without all the fuss, then the Knock Out rose is for you.

General Plant Characteristics

Knock Out roses grow to 4 feet tall and 4 feet wide. With no pruning they have reached over 6 feet at my home. A smaller bush can be maintained through pruning. They have a 5 to 6 week bloom cycle. There is no need to dead-head the blooms in order to get more flowers. They are a ìself-cleaningî rose bush and will continue to produce flowers throughout their bloom cycle.


Growing Requirements

Knock Out Roses are hardy to zone 5. They like well-drained and fertile soil in full sun. A two or three inch layer of mulch will moderate the soil temperature and conserve moisture during hot, dry weather, minimizing summer stress. In northern areas, mulch may be more important in winter, but here in the mid-South I make sure it is refreshed going into Summer.

Feeding and Watering

At planting time, use a starter fertilizer to help establish a deep root system. Water deeply after planting, and monitor soil moisture to keep it consistently moist but not wet. An established Knock OutÆ rose only requires supplemental water in the driest weather. Do not water roses with overhead sprinklers, because that can lead to leaf spot and powdery mildew. Instead, hand-water or use soaker hose. Feed Knock OutÆ roses with a rose fertilizer (organic or conventional) in spring as the foliage emerges and again after the first bloom cycle has finished.

Pruning

Prune Knock Out roses hard in the late winter by removing 25-30% of the plant, including any dead, spindly or congested branches. The branch structure after pruning should be somewhat vase shaped and balanced. Remove all pruned material from your property to minimize the chance of spreading pathogens to other roses which may not have the same resistance as the Knock Out rose.
Regular pruning during the growing season happens between bloom cycles; the primary goals being to remove spent blooms before rose hips begin to form, and size maintenance. When a rose is pollinated, the fruit that forms is called a rose hip, if rose hips are allowed to form, it greatly lengthens the amount of time between bloom cycles. Remove spent blooms to shorten the time between bloom cycles.
As for size considerations, a Knock Out rose will grow approximately 16 inches to produce itís bloom cluster; so removing 16 inches of ìbloomed-outî growth at the end of a bloom cycle will maintain the plantís current size. If your goal is to let the plant grow larger, remove only the spent blooms themselves. To reduce the size of the plant you can cut a bit more than 16 inches; however, the harder you cut, the longer and weaker the branches tend to grow back. Try to keep these mid-season prunings to 15% or less of the overall plant size. If you find that the winter pruning is not keeping the rose small enough, you may need to transplant the rose to a place with more room.

Family Members

Knock Out Roses are available in several different color and style varieties. Colors range from bright yellow, to a soft mauve, pink and deep red. They look great planted in large groups as a hedge or individually among other perennials and annuals in mixed beds and borders. Here are some of the varieties:
Knock Out Rose
Double Knock Out Rose
Pink Knock Out Rose
Pink Double Knock Out Rose
Rainbow Knock Out Rose
Blushing Knock Out Rose
Sunny Knock Out Rose

Virus Alert

In the past few years, rose rosette virus has been a growing concern for Knock Out rose enthusiasts. The virus is transmitted from plant to plant by a mite which feeds on young leaves. The disease travels through the vascular system of the plant without symptoms until it has reached the root system. At this point new growth will show signs of infection. Left unchecked, it can spread throughout the plant and to any other roses in the area.
This new disease is cause for concern because the infamous disease resistance of Knock Out roses does not prevent them from succumbing to it. Further, there is no spray or other treatment that can be applied to infected plants: they must be removed and destroyed.
The telltale signs of rose rosette include thread-like or misshapen new growth, thick stems that are densely thorny, a deep red color to the new growth (more-so than the normal red of Knock Out roses). If you notice these symptoms, get a second opinion from a trusted horticultural source, like your county extension agent, before removing the plant. If you have had an infestation of rose rosette, do not replant roses in that location for at least three years and be sure to eliminate any suckers that may sprout from the roots of the previous plant.