Last updated on December 14th, 2021
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Sunflowers are one of my favourite plants and I grow quite a few varieties and what I really like is that you can grow them without a lot of care. However, if you notice curling leaves on your sunflower leaves this usually means there is an issue.
I have also noticed that ‘Why are my sunflower leaves curling?’ is a very common question I get asked, especially for those just getting into growing these amazing plants. The good news is, if you can identify the problem and cause, you can usually get the sunflower back to its former glory and healthy again.
In the sections below are the different causes that I find often cause curling sunflower leaves but more importantly, what you can do about it.
Are the curling leaves due to over or under watering?
The first culprit and usually the most common is that they are not getting enough water, or even in some cases too much water, but this is usually because of waterlogged soil. Watering your plants is essential, however, make sure you consider the type of soil in use and that is well-drained. If you grow sunflowers in containers, also make sure you have holes in the bottom of the pot so water can freely drain away.
If the soil has poor drainage, it is easy for water to pool around the roots encouraging fungal-related problems and root rot. Roots drowning in water are unable to take in adequate oxygen, which leads to overall plant stress. You can identify if your plants are overwatered when the leaves curl inwards and begin to discolour and turn a pale yellow colour.
It is important to plant sunflowers in well-drained soil and water them regularly, especially once they are more established and this is even more important if they are planted in containers as they dry out much more quickly.
This means that you space out the watering sessions to allow the soil to absorb all the available water. When you eventually water the sunflowers, give them enough water to reach the roots deep in the soil. Alternatively, drip irrigation systems coupled with a timer will deliver the right amount of water at appointed times, this is useful for sunflowers grown in containers.
Read next: How to grow sunflowers, everything you need to know
Watch out for pests such as aphids attacking the sunflower leaves
If overwatering is not an issue, maybe pests are the issue and the good news is you can usually see them but sometimes they curl the leaves around them. Small insects such as aphids, whiteflies and thrips can cause damage to sunflowers if you get a large enough infestation. What is common about the insects mentioned is that they suck sap from the leaves.
After consuming the sap, the insects secrete honeydew, which in turn promotes the growth of sooty mould. The honeydew also attracts other insects like ants that will further affect the plant’s vigour. Inspect the underside of the leaves and the stems to gather clues and identify the pest. Once this is complete, employ natural or chemical control to prevent further damage to the sunflowers. You can usually just use a regular pesticide spray from your local garden centre or purchase them online. It might be a good idea to use a fruit and veg safe spray if you intend to eat the seeds just to be on the safe side.
Read next: How and when to collect sunflower seeds
It could be fungus disease causing the sunflower leaves to curl
While sunflowers are generally resilient they can be susceptible to several fungal attacks due to environmental causes. Even if you plant your sunflowers in well-drained soil, airborne spores can attach to the foliage and wait for the perfect conditions to germinate.
Common fungal infections in sunflowers include leaf spot that causes the leaves to discolour manifesting brown or grey patches. The patches continue to spread disfiguring the leaves and eventually causing the plant’s death in more serious cases.
There is also downy mildew and rust that manifests on the stems or foliage, this is fairly common and attacks many different garden plants.
Most can be controlled by removing affected leaves and then spraying with a general fungicide.
When handling fungal infections, dispose of the infected leaves to avoid contaminating the rest of the plants, I also don’t recommend putting them into your compost heap either.
You can learn more about why the whole sunflower plant might be wilting in this guide here
Sunflowers suffering from mineral deficiencies
If you have fairly good soil and dig plenty of compost into the soil before planting them this should not be a problem but it’s worth mentioning.
All plants need water and adequate nutrients to thrive. You should consider if the sunflowers are not getting enough nutrients and if the plant is not overwatered or suffering pest attacks. Usually, mineral deficiencies such as lack of potassium, boron, nitrogen and calcium affect the plant causing the leaves to deform and discolour.
Take note of the symptoms and any deformities so that it is easier to identify the exact issue. Conducting a soil test is a sure way of telling which minerals are missing so that you do not use the wrong fertiliser. If you confirm that it is a nutritional-related issue, use well-rotten manure to fix the problem or a recommended fertiliser from professionals.
Usually improving the soil with some compost or farm manure is enough to stop this from happening in the first place.
Diagnosing the problem causing your sunflower leaves requires a keen eye. This is because initially, the symptoms are mild and not easily identifiable. Once you have a clear indication of whether the problem is pest, chemical or water level related, choosing a form of action will be a straightforward process. If you are unsure as to the cause, reach out for professional help.
Read next: Why is my sunflower not producing flowers