Light

• Knock Out roses produce beautiful flowers when given at least six to eight hours of full sun. Plants in shaded areas or those in prolonged cloudy weather will not flower as well as roses in sunny spots.
  
  

Soil

• Most roses, including Knock Outs, prefer a well-drained soil with a pH of 6.5. Deep watering is important for roses, especially during flowering. A lack of blooms can indicate the plants are unhappy with the soil type or moisture level.
  
  

Pruning

• Pruning in late winter invigorates flower production for plants that bloom in summer. Knock Out roses should be pruned back by one-third in late February, according to the University of Arkansas Extension. For northern gardens, pruning should wait until the conclusion of harsh winter temperatures.
  
  

Fertilization

• Lackluster blooms on Knock Out roses may point to insufficient nutrients. Plants will flower best when supplied with phosphorus in amounts that are similar to or greater than the quantity of nitrogen.