My Double Knock Out Rose Leaves Are Yellow

Season and Zone

• Roses grow and bloom from spring to fall and enter a winter dormancy in cold weather. Yellow foliage after the first fall frost simply indicates the end of the growing season. Knock Out roses are hardy to U.S. Department of Agriculture growing zone 5, so yellow foliage in zone 4 or lower may indicate bush suffering or death. Move Knock Out roses into the house or garage in lower zones for protection.

Site and Sunshine

• All rosebushes require at least six hours of sun every day for growth and blooming. They also require good air circulation and complete site and soil drainage. Knock Out roses in shade experience depleted chlorophyll, which leads to yellowing, while roses in still air or standing water begin to rot and yellow. Move the rosebush to a more appropriate site to remedy this situation.

Nutrition

• Rosebushes are hungry and thirsty, and they turn yellow with lack of nutrition. They also yellow, though, with incorrect nutrition or fertilizer applications. Mix 6 inches of organic compost into the top 12 inches of soil at planting for loose, moist and nutritious soil from the start. Give rosebushes granular or water-soluble fertilizer made for acid-loving plants for ideal nutrition. Granular fertilizer can burn rose foliage, though, so don't overfeed the bushes. Keep fertilizer granules at least 6 inches from any rose foliage for protection.

Disease

• Knock Out roses boast disease resistance but may still fall prey to some standard rose garden infections. Powdery mildew, black spot and rust all attack rose foliage with fungal infections. They produce powdery white film, black ink spot formations and orange growths on leaves, respectively. Although these diseases don't kill the plants themselves, they do lead to leaf yellowing and death, resulting in defoliation. Treat and prevent these types of disease with regular fungicide applications, pruning and responsible garden cleanup.