Sunflowers are loved by many of us both because of their beauty and because of their delicious and nutritious seeds. But sometimes, during harvest, you notice that some sunflower seeds are empty.
Why are sunflower seeds empty?
Seed wilting (seed growth and development within the shell) is not only a problem for home gardeners, but also for farmers who grow this crop commercially. Being empty of sunflower seeds also causes a lot of economic damage for people who grow this crop for oil extraction. Research on sunflower seed embryo development is ongoing, but several possible factors are the main reason why sunflower seeds are empty.
1. Heat or drought stress after pollination
High heat or drought can reduce the yield of plants and this is also effective for sunflowers. Heat waves or drought stress the plants and grain filling is reduced. The process of seed development is complex and involves the production and translocation of photosynthetic products as well as processes within the seed itself. If you had very hot and dry days at the time of pollination, this is probably a factor in causing the sunflower seeds to be empty.
To reduce the effects of heat, you can water the sunflower deeply because this plant has deep roots. If your cultivated area is small, you can also use a shade to reduce the effects of heat.
2. Pest damage
If you notice a small hole in the empty seeds, you most likely have a pest problem. Sunflowers are relatively resistant to pests, with the exception of a few species of insects, the most troublesome of which lay eggs on the bracts and whose larvae actually eat the developing seed.
The two main culprits are Smicronyx fulvus and Smicronyx sordidus. These pests feed directly on the growing seed, then chew the husk and fall to the ground and find a place to spend the winter and emerge as adult insects the following summer.
If the number of damaged seeds You can use organic insecticides to control it. It is best to spray when the flowers are just opening, as the same insecticides can kill beneficial pollinators and parasitic bees. So use natural pesticides that are less dangerous as much as you can.
3. Lack of phosphorus or nitrogen
Nutrient deficiency often leads to empty seeds in the seed. Phosphorus, along with nitrogen and potassium, is one of the key macronutrients for all plants, but it is especially important for fruit and seed development. However, nitrogen also plays a key role in seed filling.
Nitrogen is more important for leaf and stem growth, however, seed filling depends on photosynthesis. Nitrogen ensures healthy leaf growth and metabolism in your sunflowers. Studies have shown that increased nitrogen has a positive effect on sunflower yield, especially during seed filling.
Feed sunflowers with a high-nitrogen fertilizer early in the growth phase, when the leaves are developing. Use a good slow-release fertilizer monthly (or as directed) or use a fast-acting liquid fertilizer every 7-14 days. As the plants reach their mature size, use a high phosphorus fertilizer to feed the bushes.
4. Lack of sunlight (low light or defoliation)
Nitrogen is essential for healthy leaf growth. Leaves are the main photocenter in the plant. Therefore, any factor that affects the growth of leaves leads to the emptying of sunflower seeds.
Several studies have investigated the effect of defoliation (removal of leaves) on this plant and concluded that plants that If they have lost their leaves or grown in low light, not only will they have a lower yield, but their seeds will be empty. For this plant, the more sun, the better it grows. If you plant several rows of sunflowers, be sure to consider the appropriate planting distance so that some plants are not in the shade. For large varieties, about 3 feet (1 meter) apart is recommended, but you can plant them a little closer and still get a good harvest. In case of row planting, try to plant them from east to west so that they can receive enough sunlight from the south.