Knockout roses are most diseases and stress-tolerant flowers. They can cure most of the common problems themselves. Yes! It is true. But sometimes they also need help to solve some problems such as yellow leaves.
Yellowing leaves are a common sign of many problems. Improper watering, fertilizing problems, environmental stress, lack of light, insects, and diseases can be the cause of yellowing leaves on knockout roses.
The problem is one but the reasons are many. So, you should find out the exact reason for yellow leaves before treating the plant. Because you know; wrong treatment always harmful for the plants.
For your convenience, here I have discussed every possible reason for the yellowing leaves of knockout roses. I hope it will help you find the problem and solution to treat your plant successfully.
So, without losing your time, let gets started-
Yellow Leaves on Knockout Roses-Causes &Treatment
Chlorosis is the most possible reason for the yellow leaves of knockout roses. In simple words, chlorosis means yellow leaves for the lack of chlorophyll. It is grouped into General Chlorosis and Interveinal chlorosis. Let’s see what are the causes of chlorosis-
Causes of Chlorosis
Nitrogen or oxygen and iron deficiency are the reason for general Chlorosis and Interveinal chlorosis respectively.
Interveinal chlorosis is more complex than general chlorosis. Because soil pH also involves in interveinal chlorosis. Knockout roses can’t take the required iron if the soil pH is too high.
If the pH remains in the optimum range(6.0 to 6.5), then the soil has not enough iron for knockout rose bushes.
Compact soil, high salt, and other micronutrients deficiency in the soil can be the reason for interveinal chlorosis.
Identification of Chlorosis
See the veins of the leaves, if it remains green but the leaves turn yellow and curl, then iron deficiency may be the cause of chlorosis. Also remember, young and upper leaves will become yellow because of the iron deficiency.
If the leaves turn yellow with the veins, then it may happen for poor aeration and oxygen.
But If you notice the lower or older leaves become yellowing, then poor nitrogen is the culprit.
Interveinal Chlorosis-Knockout roses grow and thrive well in slightly acidic soil. Take your pH meter(our pick: Atree Soil pH Meter) and check the soil pH. If the pH is high, then add soil acidifier (our pick: Jobe’s Organics Soil Acidifier) and if you see the pH is lower than the optimum pH, add garden lime(our pick: Jobe’s Organics Garden Lime) to adjust the soil pH.
After adjusting soil pH, apply iron tone(our pick: Espoma IT5 Iron Tone ) or chelated iron to your knockout roses.
If everything seems complex, here is a quick and easy solution. Mix 1/4 teaspoon of chelated liquid iron(our pick: Southern Ag Chelated Liquid Iron) into the water and feed your plant.
General Chlorosis-Feed nitrogen-containing knockout rose fertilizer or sprinkle coffee grounds around the plant.
Improper watering involves poor and overwatering. Both are the cause of yellow leaves and both show the same symptom.
Causes of Yellow Leaves for Improper Watering
Photorespiration is the natural process of removing excess water from the plant. If the photorespiration rate is higher than the available water, plant leaves wilt and turn yellow.
In contrast, overwatering decreases the air space in the soil as well as the oxygen level. As a result, the leaves become yellow.
Identification of Poor and Overwatering
Poor Watering-Poke the finger or dry wooden stick into the soil. If you feel the dryness, then apply water you knockout roses to revive them. To get the accurate result, use a moisture meter.
Also, remember; soft stems and shoots become droopy before the leaves yellowing because of poor watering
Over Watering-If you see the soil contains sufficient water and the stems of the plant are still firm but leaves are turning yellow, then overwatering is the cause of the problem.
Less water more frequently. This the basic rule of watering to the knockout roses. Apply 8-10 inches of water once per 2-4 days to protect the plant from improper watering.
Also, consider the drainage facilities of the container and potting soil. Always plant your knockout rose plant in good potting soil.
Learn more about the potting mix for roses- Best Potting Soil for Roses-Buying Guide and Recommendation
3.Problems On knockout Rose Fertilizer
Improper feeding may be the cause of the yellow leave of knockout roses. You know, nitrogen deficiency can be the reason for yellow leaves.
If you notice lower leaves are truing yellow but upper leaves remain green, then the plant needs nitrogen to develop chlorophyll.
Apply coffee grounds on the soil of rose bushes and water. The coffee ground can feed nitrogen to your plant. You can also feed commercial knockout rose fertilizer.
4.Insects and Pests
Pests and insects can damage the knockout rose plants by yellowing the leaves. Japanese beetles, Rose scales, Rose leafhopper, Slugs, Aphids, thrips, sawflies, and grasshoppers are the major pests of knockout roses.
They penetrate their sucking type mouth into the soft stems and leaves and release toxin substances into the plant tissue. As a result, the leaves become yellow and fall off.
Most of the rose insects hang on the underneath of the leaves when they aren’t active. Check the under surfaces of leaves to confirm the yellowing leaves for insects or not.
Way to Get Rid of Insects
Apply neem oil, insecticidal soap, or other rose insecticides on the leaves of the knockout roses. You can also mix up both neem oil and insecticidal soap for better and quick results.
If you have not enough time to make your insecticidal soap or neem oil recipe, buy the readily available neem oil or insecticidal soap for your knockout rose plant.
Some diseases can be reason of yellow leaves. Black spot is the major fungal disease of rose that can turn the leaves yellow. At first, you will notice some black spots on the leaves. After a few days, the leaves become yellow and fall.
Remove the affected leaves carefully and destroy them. Spray neem oil or rose fungicide to control the diseases. Remember; fungicide can work well in the early stage. So, it will be wise to apply a fungicide as a preventive spray.
Knockout roses need at least six hours of sunlight to thrive and bloom. Lack of sunlight reduces the rate of photosynthesis that turns the leaves yellow. Heat stress is another cause of yellow leaves.
Plant knockout roses where they can get a minimum of 6 hours of sunlight in a day. Never park your car in front of the roses for a longer period of time.
Don’t water your knockout roses in hot weather. Early morning or evening is the best time to water the knockout rose plant.
You can also apply light-colored mulch to protect the plant from heat stress.
Don’t worry about the yellow leaves on knockout roses. It can solve easily. To get rid of this problem- Feed fertilizer regularly, water them properly, apply insecticide, and fungicide by following the label directions.
I hope you will get a healthy knockout rose with lots of long-lasting beautiful blooms again.