Sunflower (Helianthus annuus L.) belongs to family Compositeae. It is a native to Central America, and seemingly; it is Peruvian or Mexican in origin 12.

The economic importance of this crop is that the fresh green plant can be used as silage or fodder to feed livestock. The seed can be eaten raw or roasted, and it can be used in salads, cooking, margarine, lubricant, paint varnishes and soap production. The seed contains about 36 to 45 % oil depending on the variety 3.

The crop is categorized as a low to medium drought sensitive 4. It shows adaptability to different regions, climatic conditions and sowing dates due to its high genotype and ambient interactions 5. Therefore it can be grown twice a year 2. Nevertheless, despite the ability of the crop to high water use, and the ability to withstand short periods of severe soil water deficit of up to 15 atmosphere tension, the long periods of severe soil water deficit, particularly at water-sensitive growth stages, causes significant reduction in seed yield 6.

It is noticed that good cultural practices and drainage are required for sunflower production 7. However; several studies reflected that sunflower can be grown at a wide range of dates. Most cultivars are early maturing. In areas where no winter, sunflower can be grown at any month of the year to obtain satisfactory yields 89.

It is reported that yield differences between hybrids with regard to sowing time and density are remarkable. These differences are determined on one hand by the hybrid characteristics and environmental conditions, and on the other hand, on by plant population, soil fertility and land preparation 89.

Researchers 10 showed that when sunflower sown in December; it flowers between March and April, at a time when the honeybee activity is maximum, resulting in better pollination and consequently good seed setting.

Seed setting and filling problem is one of the most important constraints in sunflower production, especially under rain-fed; where the heavy rains wash the pollen grains, and often considered to be a major reason for low productivity 11.

This experiment was conducted at the farm of the College of Agricultural Studies, Sudan University of Science and Technology, Shambat, Khartoum - Sudan, during the seasons 2014/2015 and 2015/2016. Where the climate is described as semi-arid region. The area receives an average annual rainfall in summer, during July to September, ranging from 100 to 160 mm/annum, and relative humidity ranges between 31-51% during the wet season and 12-27% during the dry season. The average maximum and minimum temperature is about 41.7 ⁰C and 15.3 ⁰C respectively. The winter season begins in November and ends in March. It is relatively cool and dry 12.

The soil of study area is classified as silt, clay loam with non saline at surface, but slightly sodic at the subsurface.

The adopted experimental design was the randomized complete block (RCBD); with four replications and three treatments (sowing dates (March, May and July)) which referred as S₁, S₂ and S₃ respectively.

The land was cleared, well prepared by using disc plough, disc harrow, leveler and moldboard. Then the area was divided into equal plots. Each plot size is 4 X 4 m², with 5 rows. The spaces between rows are 70 cm. Following the randomization, seeds of sunflower (Hysun 33) were sown on rows, 70X15 cm apart. The recommended cultural practices by the Research Centre in Sudan were followed.

The data of the studied parameters were collected. Where three plants were randomly selected from each plot for measuring the following parameters: plant height (cm), leaf area index (LAI), plant dry weight (g), and yield components including head diameter, 100 seeds weight (g), number of seeds/head, yield (t/ha). The collected data were subjected to statistical analysis using statistic 8, Version 2.0 UK.

Sunflower can be cultivated year a record in different region in the world. The performance of sunflower is largely affected by adverse conditions, cultural practices and sowing date.

This Study showed that the optimum sowing dates in the study area are May (S₂) and July (S₃), when the highest plant height, leaf area index (LAI), number of seed setting/head, weight of 100 seed, head diameter, dry weight were a obtained.