My Knock Out roses are looking very bad. The leaves are falling off and turning yellow. They bloomed really early this year. They looked very pretty, then everything went wrong.
The Gardener’s Answer
Hello, Alberta in Missouri: Knock Out roses are for the most part low-maintenance and disease-resistant shrubs that provide wonderful color all season long if they are happy. Are these new plantings or older, more established ones? Typically when we see plant foliage begin to yellow it has to do with too much moisture or lack of nutrients. This is a symptom of chlorosis, which is a lack of iron in the soil, but yellow foliage can also be associated not enough nitrogen. Are your roses growing in a soil that does not drain well or have you had an extremely rainy season? If so then you may need to amend the soil with something like Permatil, an expanded slate material that helps to improve drainage. When soil becomes water logged it decrease air movement, which is essential for plant health. If your roses are growing in well-drained soil and full sun then the issue may be a nutrient deficiency. To find out you can contact your County Cooperative Extension Service and ask about having your soil tested. They typically charge a nominal fee and the results may take a couple of weeks to get back, but it’s worth the time and effort to keep your plants happy. For now be sure to clean up all fallen plant debris. This is a great environment to insects and disease to live.