Sunflower Leaves Yellowing: Why Are My Sunflowers Leaves Turning Yellow

The sunflower plant, also known by the scientific name Helianthus annuus, is one of the most striking and beautiful plants that we can choose to decorate both our home and our garden. However, sunflower leaves yellowing is a common problem. If your sunflower leaves are turning yellow, you are in the right article to know “why are my sunflower leaves turning yellow”.

Do you know what is the Ukraine national flower? Sunflowers are the National flower of Ukraine

When Sunflower Leaves Turn Yellow

Sunflower leaves turning yellow may be due to the normal cycle of life of the sunflower plants. Therefore, to understand what is behind the question which triggers this article about Why Are My Sunflowers Leaves Turning Yellow, we need to understand first the cycle of life of the sunflower plants.

Sunflowers will need between 90 and 120 days from sowing to harvesting. With warm temperatures and high luminosity, this time is shortened. However, it is longer if the weather is cool and not very bright.

In mild weathers, sunflowers are usually ready to harvest in late summer or early fall.

Therefore, to understand whether yellow leaves are due to growth problems or because the harvest is approaching, we must first differentiate at what stage of the sunflower plant’s cycle we are in.

When Sunflower Leaves Turn Yellow. It will not be the same to detect sunflower first leaves turning yellow, sunflower seedling leaves turning yellow, or a plant with seeds with sunflower leaves turning yellow and falling off, turning brown and getting dry. They are different stages of the sunflower cycle until we get sunflower seeds to harvest.

So, we will look at the stages. As you can see in the scheme, when the sunflower plant is mature and approaching sunflower harvest time, the appearance of the sunflower plant changes drastically. So, the right question to understand is not Why are Sunflower Leaves Yellowing, it is When do Sunflower Leaves Turn Yellow.

When Sunflower Leaves Turn Yellow? By the time the sunflower plant is in active bloom, it is a critical time for the plant and various nutritional imbalances can occur, among other factors that may cause sunflower leaves to turn yellow.

Sunflower flowering depends on many factors such as planting depth. It seems that the depth of planting has an influence on the earliness of flowering, being earlier when the planting is shallower.

So, we see very early flowering in baby sunflowers or potted sunflower plants purchased in supermarkets. Decoratively they are beautiful but I am sorry to say don’t get your hopes up thinking you will get sunflower seeds. They are ornamental plants, and will rarely make the life cycle of a sunflower plant.

Another peculiarity of the sunflower plant that can be reflected as yellow leaves around flowering time is the so-called “photoperiod”. The photoperiod is the number of daylight hours per day, which influences the flowering date of the sunflower. Consequently, the sowing date and the latitude of the site will be decisive, since the photoperiod depends directly on them.

In early sowings, when the days are very short, the plants will need more time until flowering. On the other hand, in late sowings, when the days are long, the plants develop and flower much faster.

Temperature is another important determinant for flowering and therefore for the presence of yellow leaves due to any possible deterioration of nutritional deficit in the sunflower plant.

In the case of the sunflower plant, it requires an accumulation of hours of heat. That is to say that the sunflower plant blooms once it has accumulated a certain number of degree days. The average temperature of each day is added, counting from the sowing of the sunflower, and when a limit is reached, the plant enters flowering. Normally, this limit is between 1000 and 1500 degree days.

Sunflower Leaves Turning Yellow and Brown

As harvest time approaches, sunflower leaves turn yellow and brown, and so do the characteristic yellow petals, which are not actually true petals. Those yellow petals are shed from the flower head (which is the large flower head) once pollination is complete. They are no longer needed to attract pollinators. At that time, the sunflower seeds are not yet fully formed, so you still have to wait a little longer.

You will also notice that as the time of sunflower harvest approaches, the sunflower, which during its initial growth-oriented its flower head towards the sun, stops making this movement. When the sunflower is growing, it orients its flower head towards the sun in the morning, pointing towards the sunrise, and once the sun rises, it follows the sun throughout the day.

This movement of following the sun ends once flowering has come to an end. The flower remains oriented towards the sunrise and no longer follows the movement of the sun. Over the days, as the sunflower seeds mature, the sunflower tilts downward, facing slightly to the ground.

Sunflower Leaves Turning Yellow and Brown. It is after stopping follow the sun and when yellow petals are gone that sunflower leaves are turning yellow and brown. The sunflower leaves turn yellow and brown and dry out.  The sunflower plant turns light brown or grayish brown, and to the touch, they feel dry and brittle.

Although it is not entirely necessary to reach this point, eventually all the leaves of the plant will be shriveled and hanging from the stem. This is definitely the appearance of a dead plant. It is best to harvest a little earlier to avoid plant drops and seed shedding.

Sunflower Leaves Yellowing – Why Are My Sunflowers Leaves Turning Yellow

Now that we know the cycle of life of the sunflower plant, let’s move forward to our key question. Why are Sunflower Leaves Yellowing? In the following paragraphs, I summarize what causes sunflower leaves to turn yellow and how to fix sunflower leaves’ yellowing.

If you need to review and regrown sunflowers again, I recommend this article How to Plant Sunflower Seeds

Location for Sunflowers

Before we start talking about why are my sunflower leaves turning yellow, it is important to know the correct location of the sunflower. The sunflower needs a lot of sunlight because without a good supply of light it will not be able to develop and bloom properly.

Where to place potted sunflowers? The ideal is to locate the sunflower outdoors in the sunniest area of our garden.

Potted sunflowers indoors. If we want to have a sunflower plant indoors you should place it near a window where it has many hours of direct light for at least 6 hours a day.

On the other hand, for sunflower in a pot, we will need the pot to be large and deep. We recommend planting the sunflower in the place where it is going to be since it does not support transplants well. If your sunflower has good light and space to grow it is unlikely to have yellow leaves.

Now let’s see why are my sunflower leaves turning yellow, which causes Sunflower Leaves Yellowing

Sunflower Leaves Yellowing due to Nutrient Deficiencies

Sunflower Leaves Turning Yellow due to Nutrient Deficiencies. Nutrient deficiencies in plants produce symptoms on leaves, such as necrosis (black dead tissue), shriveling, or yellowing.

There are many types of deficiencies, but the main ones that cause yellow leaves or chlorosis are those of nitrogen, phosphorus, magnesium, iron, or manganese.

As with water, the sunflower is a plant that consumes large quantities of nutrients. Although it tends to find them easily even in soils that have not been recently fertilized, due to the great depth and surface area explored by its roots.

The application of fertilizers and fertilization of sunflowers will be more important at the beginning of the crop and in the superficial layers of the soil since it will be there where the young plants have their roots before they acquire their full potential.

Sometimes it may seem that it does not respond to fertilization because it actually extracts nutrients that had been incorporated into the soil long before, which other crops could not take advantage of. Also, young sunflower plants take advantage of the nutrients located in the shallower soil layers to a greater extent.

How to Fix Sunflower Leaves Yellowing due to Nutrient Deficiencies

The sunflower plant has a great capacity to deplete soil nutrients, especially phosphorus (P) and nitrogen (K), and although sunflower consumes much more potassium (K) in proportion, this will return to the soil if the crop residues are incorporated into it.

So, we must be very attentive that both flowering and seed maturation processes, especially if the seeds are used to extract oil, fertilization is key in the development of the plant. As we mentioned before, one of the most common causes of yellow leaves in sunflower is the deficiency of any nutrient, especially phosphorus, nitrogen, and/or potassium.

How to Fix Sunflower Leaves Yellowing due to Nutrient Deficiencies. Sunflower seeds have a good supply of phosphorus, nitrogen, and potassium, especially in their growth stage. To prevent sunflower leaves from yellowing, we recommend measuring the pH of the soil and applying a 10-10-10 fertilizer.

For large-scale sunflower crops, there are other fertilizer options that the market is evaluating. Here, for example, we see the results of this field study with sunflowers using nano fertilizers.

Nano fertilizers have recently been introduced to intensify the production of certain food crops although there is still not enough information. We liked this scientific article because it compares the effects of two nano fertilizers on the production of common sunflower under field conditions. And the results show significant differences, with very encouraging results, between these two experimental treatments in the diversity, proportion, width, and length of trichomes, flower bud development, etc.

The ZnO-NPs treatment induced the best sunflower responses, while TiO2-NPs mainly affected quantitative and nutritional parameters such as oil content and shifted sunflower physiology towards early maturity. Regarding the important question of whether there are traces of these nano fertilizers in the edible portions, the study showed that no titanium or zinc accumulation was detected in sunflower seeds and our positive results encourage further research on nano fertilizers.

Let’s continue getting to our main question. Why are Sunflower Leaves Yellowing? What causes sunflower leaves to yellow and how to prevent them from yellowing in the future.

Sunflower Leaves Turning Yellow due to Overwatering

Sunflower Leaves Yellowing due to Overwatering. Like all plants, sunflowers need water to survive and develop. However, too much water is not good for the sunflower plant.

Overwatering can generate too much moisture and fungus can easily grow and which causes sunflower leaves yellowing.

On the other hand, too much water will also rot the sunflower roots and this will cause the plant to start rotting and yellow leaves to appear on the sunflower.

How to Prevent Sunflower Leaves Yellowing due to Overwatering

The best way to avoid these problems of excess moisture or over-watering is to verify that the soil is dry before watering our sunflowers.

You should use a moisture tester to see if the soil is ready to be watered again or if you should wait a little longer to water your sunflower.

Sunflower Leaves Turning Yellow due to Excess Heat

Sunflower Leaves Yellowing due to Excess Heat. Excessive heat will also cause yellow leaves on sunflowers.

Sunflowers like warm weather and sunshine but too many days of extreme heat will also damage the sunflower.

How to Prevent Yellow Leaves on Sunflowers Due to Excess Heat

How to Prevent Yellow Leaves on Sunflowers Due to Excess Heat. Be sure to water sunflowers properly when they are going through several days of extreme heat. It is best to water sunflowers early in the morning or in the evening when the sun is no longer strong.

Remember not to overwater either, otherwise, molds may appear due to excess humidity or the roots of the sunflowers may rot and yellow leaves may appear.

Sunflower Leaves Yellowing Due to Pest and Diseases

Sunflower Leaves Turning Yellow Due to Pest and Diseases. As we have already explained above, an excess of irrigation can produce the appearance of fungi in sunflowers. Also, sunflowers also suffer attacks from pests such as spider mites and aphids.

Aphids, mites. and spider mites feed on the sap of our sunflower and take away nutrients, so the sunflower will have yellow leaves.

How to Fix Sunflower Leaves Yellowing due to Pest and Diseases

We should inspect the sunflower plant to see if the yellow leaves are due to an insect attack.

Usually, these insects damage the leaves or are found on the back of the leaves.

We can easily eliminate the insects with neem oil for plants which is an ecological and organic oil that will not harm the sunflowers.

Sunflowers Leaves Turning Yellow Due to White Mold

​​​​Sunflowers Leaves Turning Yellow Due to White Mold. Sclerotinia sclerotiorum Diseases of Sunflower​ (White mold)

Verticillium Wilt Symptoms – Sunflower Leaves Turning Yellow And Brown

Sunflower Leaves Turning Yellow And Brown due to Verticillium. Infected leaves have a mottled look due to tissue between leaf veins becoming yellow and then brown.