The most likely cause of sunflower leaves turning yellow is overwatering. Sunflowers react badly to overwatering and poor drainage. If you’re sure that your sunflowers haven’t been overwatered, the discoloration may be a result of nutrient deficiency, disease, or pests.
Sunflowers are the pride of your garden when cared for correctly, standing proud and strong. For me, these tall flowers standing at my gate are one of my favorites. With years of care, I’ve built up a list of this flower’s most common causes of yellow leaves.
Joyful Sunflowers
There are so many great reasons to grow sunflowers. They are incredibly cheerful and beautiful, making great cut flowers. Their unusual feature of heliotropism (following the sun) makes them an even more delightful sight.
Not only this, but they help out other plants in your garden by attracting bees, birds, and other pollinators and also helping to detoxify the soil.
They can absorb toxic contaminants such as zinc, chromium, and copper, preventing these elements from polluting your garden.
Overwatering
Sunflowers absolutely hate standing in puddles, so take great care not to overwater them. If you are a beginner gardener watch out for this, as it’s probably the biggest mistake newbies make. This is the most common cause of yellow sunflower leaves.
Overwatering is such a problem for the sunflower because they are very susceptible to root rot. Sunflowers have deep roots, so give them a large drink of water each time, but ensure the topsoil is completely dry before their next one.
Remember, it is rare that sunflowers will die from underwatering, but likely with overwatering, so less is better in this case.
If you think you may have overwatered your sunflower, take a decent break until you water the flower again. Once your sunflower is back on an appropriate watering schedule, the leaves should return to a normal color.
Nutrient Deficiency
If your sunflower is lacking in nitrogen it may display yellow leaves. If the yellowing is caused by nitrogen deficiency, the leaves will still be green near the veins.
If this describes your sunflower leaves, check the soil’s nutrients with a soil test kit. If the soil is lacking nitrogen and the sunflower is severely yellowed, add a dose of 10-10-10 fertilizer to the plant’s soil immediately.
If the sunflower is lacking phosphorus, another key nutrient, you will see a reddish-purple color instead. This deficiency can be solved using the same method.
Sunflower Diseases
There are a couple of diseases that sunflowers are especially susceptible to, fungal rot and downy mildew. Here’s a guide to spotting them, and what to do if you do.
Fungal Rots
If your sunflower’s soil doesn’t have proper drainage, or the sunflower is too often overwatered, it is very susceptible to root rot. A change in the leaves is one of the first indicators of this disease. They may start to look dull, or suddenly turn yellow.
Unfortunately, if root rot has developed in your sunflower, the best solution is to dig it up and dispose of it so that it doesn’t spread to the other flowers. You will see that the roots are black, brown, or decayed.
To prevent future root rot, ensure that you are planting sunflowers in very well-draining soil, and ensure to space out watering sessions.
Downy Mildew
Another reason to limit watering sessions is downy mildew, another disease that thrives in wet conditions and threatens your gorgeous sunflowers. As well as yellow, discolored areas, you may notice a gray, purple, or brown fuzz on the underside of the leaves.
Fortunately, this condition can be treated if caught early. From this point on keep moisture off of the plant itself, especially the leaves, and water the plant from below. Spray the plant with a mixture of baking soda and water. When the weather gets warmer the condition will clear up as it doesn’t survive well in the heat.
Preventative measures can also help protect your sunflowers in the future. Good garden hygiene, such as removing dead material, can stop the spread of this disease. There are also preventative treatments and genetically resistant varieties of sunflower that can be used.
Sunflower Pests
If you see any signs of pests on your sunflower it’s a likely cause for the yellow leaves. This is because pests feeding on your plant drain the nutrients from it. These are the two biggest ones to watch out for.
Aphids
These tiny insects feed on the sap of the sunflower. As well as yellowing, the leaves may respond by curling or distorting. You might also see a sticky substance called honeydew on the flower, created by the aphids. This can attract mold or ants.
Many aphid infestations can be dealt with by simply spraying a strong jet of water to wipe them from the sunflower’s surface. If you want to employ stronger methods, you can use insecticidal soap or horticultural oil to kill them.
Spider Mites
These minuscule creatures also feed on sunflowers and can cause leaves to turn yellow, red, or brown. You might also spot the fine webs that they weave across the plant.
If you are dealing with spider mites, do not use an insecticide. This can actually increase their numbers by killing off any natural predators. Instead, use a horticultural oil designed for spider mite treatment, or a sulfur spray.
Frequently Asked Questions
Q: Should I cut away dead leaves on my sunflower?
Yes, it’s a good idea to prune sunflowers to encourage healthy new growth.
Q: Can my sunflower get too much sun?
A: Sunflowers love the sun, but too much heat may adversely affect them. They may begin to wilt if temperatures reach over 85 degrees Fahrenheit.
Q: How should I grow a sunflower in a pot?
A: There are varieties of sunflowers available that do well in a compact area so that you can add their cheerful appearance to your patio or balcony.
Sunflower Leaves Turning Yellow – Conclusion
If there’s only one thing you take away from this about looking after your sunflowers, it is to take care watering them!
If you notice yellowing leaves then overwatering, or a disease caused by overwatering is the most likely cause. If the yellow leaves are caused by insects, don’t panic as the situation can be easily solved,
Hopefully, this has helped you diagnose your sunny friends and you can get them back to full health in no time.