Brown Spots On Knockout Rose Bush: Reasons For Knockout Roses Turning Brown

Brown Spots On Pink Knockout Rose Bush
(Image credit: JENNIFER E. WOLF)

Roses are among the most common garden plants. One specific type, called the “knockout” rose, has gained immense popularity in home and commercial landscape plantings since its introduction. That said, knockouts with brown leaves can be concerning. Learn the reasons for this here.

Knockout Roses Turning Brown

Developed by William Radler for its ease of growth, knockout roses are known for their supposed resistance to disease, pests, and environmental stressors. While the beauty of roses without any special care may sound like an ideal scenario, knockout roses are not without problems. 

The presence of brown spots on knockout roses may be particularly alarming for growers. Learning more about brown leaves on knockout roses and their cause can help gardeners to return their bushes to optimal condition. 

Like many issues within the garden, the reason for knockout roses turning brown is often unclear. However, careful observation of the plant and current growing conditions can help to better determine the possible cause of knockouts with brown leaves. 

Reasons for Brown Leaves on Knockout Roses

Foremost, growers should monitor the plant for sudden changes in growth habits or flower formation. These are often among the first signs that rose bushes may be infected with various rose diseases. Like other roses, botrytis and black spot may also become problematic with knockout types. Both diseases can cause the browning of leaves and blooms. 

Fortunately, most fungal diseases can be controlled through the use of fungicides specifically formulated for roses, as well as through consistent pruning and garden clean-up. 

If knockout rose leaves are browning and no other symptoms of fungal infection are present, the cause is likely related to stress. Drought and high heat are among the most common issues which may cause brown spots on knockout roses. During this time, the plants may drop old leaves in order to direct energy towards supporting new growth. If the garden is experiencing a prolonged period without rain, consider irrigating the roses on a weekly basis. 

Lastly, brown leaves on knockout roses may be caused by soil deficiencies or overfertilization. While insufficient soil fertility can cause browning leaves, so too, can the addition of too much fertilizer. To best determine the problem, many growers opt to test their garden soil. A continued deficiency or imbalance in the soil throughout the growing season may cause plant growth to slow or become stunted.

Tonya Barnett

Tonya Barnett has been gardening for 13 years. Flowers are her passion. She has transformed her backyard into a cut flower garden, which she regularly chronicles on her YouTube channel