Sunflower: When Should You Sow It?

The sunflower's homeland is considered to be the southwestern part of North America, where its wild forms still grow today. The study and breeding of the crop dates back to the 19th century, when a peasant from the Voronezh province, D. Bokarev, made the first attempt to produce oil from the seeds of the “sun flower”. The most significant contribution to the study of sunflower and the creation of high-oil forms was made by the famous scientist V.S. Pustovoit. It was from that time that intensive research on sunflower breeding and cultivation technologies began.

Sunflower Advices to the agronomist
Published by: 21.03.2019

Scientists around the world have conducted a large number of studies on crop cultivation technology to ensure the realization of the maximum potential of a particular genotype

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There is a lot of controversy about the timing of sowing modern sunflower hybrids - we will try to draw some parallels.

The main factors affecting plant growth and development are:

  • temperature
  • presence of moisture
  • availability of batteries
  • solar insolation...

One of the famous sunflower breeders and researchers Singh B. D. formulated the definition of resistance to heat and cold: «Each plant species, the genotype itself, has an optimum temperature range for its normal growth and development; the specific temperatures will depend not only on the genotype, but also on the stage of growth and development of the genotype. When temperatures fall outside of this optimal range, temperature stress occurs, i.e., temperatures that create barriers to productivity».

Temperature stress can be divided into three categories:

  2. Heat stress
  3. Stress of hypothermia
  4. Stress of freezing

It should be noted that active cell division (mitosis) in plants occurs at temperatures >+7°C, so for comfortable growth and development of the seedling, the optimal temperature is required first and foremost.

That is, early sowing is a risk of hypothermia stress, as average daily temperatures are unstable and there are drops from +14...+18°C during the day to -2...-4°C at night.

Early sowing is a risk of “freezing stress” and, accordingly, fatal consequences for the plant, as spring frosts in Ukraine are possible in March and early April.

Breeders are conducting a lot of research to improve sunflower culture and the tolerance of new hybrids to low temperatures, as this is required by modern production due to climate change on the planet and extreme conditions of sunflower cultivation in many regions of the world.

When discussing the resistance of sunflower to low temperatures, it is worth quoting the well-known author Singh B. D.: “In many environments, yields are limited by low temperatures. When the temperature remains above the freezing point, i.e. >0°C, it is called chilling, while freezing is characterized by temperatures below the freezing point, i.e. <0°C”.

According to Prof. Dragan Škorić, the world has created sources of sunflower resistance to low temperatures that can withstand frosts down to -20°C and with a degree of overwintering of 52-63%. This breeding material is used by scientists to create winter genotypes and genotypes that are resistant to low temperatures.

The literature contains data on experimental sowings in commercial production of modern sunflower hybrids before winter in November before the soil freezes and extra-early sowings in February in the steppe zone. However, the experience of growing sunflower in Ukraine and statistical data show that when sowing at a later date, with moisture in the soil, higher yields are recorded.

So, when to sow sunflower?

Sunflower seeds begin to germinate at a temperature of +3...+4°C, and seedlings appear on the 20th-28th day. The optimum germination temperature is 20°C. At this temperature, seedlings appear on the 7-8th day. Seeds that have started germinating in the soil will not be significantly affected by a temperature drop to minus -10°C. Seedlings can withstand short-term frosts down to -4°C.

The optimum temperature for growth in the first half of the growing season is about 22°C, and during the flowering-ripening period - up to 24-25°C. Temperatures above 30°C negatively affect the growth and development of plants due to heat stress.

The optimal time for sowing high-oil sunflower hybrids is considered to be a stable transition of the average daily temperature at the depth of seed placement to +10...+12°C, which allows for friendly germination by 9-12 days.

Taking into account the insufficient amount of productive moisture in the meter layer of soil in the southern and southeastern regions of Ukraine and the rapid increase in the average daily temperature in these regions, we recommend starting sunflower sowing when stable positive temperatures above +6...+8°C at night at a seeding depth of 4-6 cm with the recommended density for the region.

For the central, western and northern regions of Ukraine, this is a soil temperature of +8...+10°C at the depth of seed placement.

The biology of annual sunflower (Helianthus annuus L.) is well understood. However, the appearance of new sunflower hybrids on the market of foreign producers and their active advertising to increase sales (with not always true information about the hybrid) is a temptation for producers to make a fatal mistake when choosing the sowing dates.

VNIS recommends a balanced approach to the choice of sowing dates for a particular genotype in a particular field, based on long-term scientifically based data.