The rational use of natural conditions in agriculture requires a thorough knowledge of how cultivated plants react to permanent changes in the evolution of agro-climatic conditions as part of the ecological framework. Having a very high plasticity in terms of climate and soil requirements, sunflower has adapted to very different geographic conditions. Generally, sunflower follows the corn limits on the globe, exceeding slightly its northern limit. The July isotherm of 18 ° C is the northern crop limit, being locally specified by other factors (humidity, soil, etc.). The thermal factor limits the general area of the spread, and the humidity factor determines the areas inside the zone. Per total, the duration of the vegetation period is of about 120 – 135 days, duration that vary depending on variety and pedoclimatic conditions. The vegetation cycle of this crop distinguishes the following periods: – from sowing to arising that occurs most frequently in our country between 15.03 – 15.04 (average duration 10-18 days); – from arising to the formation of the capitulum which usually occurs between 15.04 – 01.06 and lasts for about 30 days; – from the beginning of the capitulum formation to the blooming – about 30-35 days; – from the beginning of the flowering until the end of the vegetation cycle frequently occurring in the period 20.06 – 10.09, with an average duration of 50-60 days. During this period full seed formation, growth and maturation take place. The total heat consumption, expressed in temperatures >5°C for the entire growing period, varies from one species to another between 1400 and 1800°C. In the arising – blooming period, varieties cultivated in our country require 900 ° – 1000° C. Although this crop is demanding for heat, germination can begin at 4...5 °C, enduring frosts of up to -5...-6°C (if frosts are short in time) in the first vegetation phases. However, arising occurs in good conditions at soil temperatures higher than 10°C. The limit temperature that influences the duration of the arising period is 22°C. In the case in which low temperatures persist, partial or total damage to the growth cone occurs, leading to strong branching and decreasing of production. More capitulums appear at the same plant; however, these are small, less productive, with monstrous forms. As a result of advancing in vegetation, that is, after the formation of floral buffaloes, the sensitivity of plants at low temperatures increases. In terms of average daily values, the most favorable temperatures range between 16°C and 20°C until blooming and 20°24°C from blooming to ripening. From 27°C upwards, the plants suffer and the harvest decreases. Maximum temperatures above 35°C are harmful if they occur for several consecutive days. In the case in which the heat is also accompanied by moisture deficiency in the air and soil during the filling of the grain, there occurs a forced maturation of the plants, which results into a decrease in the percentage of the core and oil. On the other hand, temperatures below 19°C during the period of grain formation prolong the vegetation period, reducing very much the content and quality of the oil. Throughout the territory of the Republic of Moldova the sunflower crop is assured with heat until the technical ripening of the seeds in 100% of years. In terms of water, the critical period for sunflower plants is triggered with the appearance of floral primordium (leaf pairs 4-6) and lasts until the end of blooming. Throughout the entire vegetation period, the distribution of moisture consumption is as follows: 29% from arising to inflorescence formation, 45% from inflorescence formation to blooming, and 26% over the rest of the vegetation period. According to experimental data, it results that the maximum consumption period of this crop takes place during the formation and differentiation of the reproduction organs, namely between stages 5-9 of morphogenesis. From a phenological point of view, it corresponds to the period of floral buffaloes formation till the end of blooming and coincides, from the calendar point of view, with June and the first days of July in the southern regions. During this critical period, which takes about 25 – 30 days, or 15% of the entire vegetation period, 50% of the water required from sowing to harvesting is consumed. In this period, the growth rhitm of vegetative mass is also the most intense compared to the rest of the period. In our country, the critical period ends, as a rule, earlier than the terms of July's severe droughts beginning. Since the humidity of the soil during the first part of the warm season (April-June) is strongly influenced by the cold season precipitations, the humidity reserves in the critical period depend very much on fallen precipitations during the accumulation period (October-April). During the rest of the vegetation period, the soil moisture influences vegetation and harvest, but to a lesser extent than in the critical period (for exemple in the interval from arising till the critical period, the plant consumes about 25% of the necessary amount for the entire period of vegetation and an almost equal amount in the period from the end of blooming to maturation). Sunflower is generally considered a drought-resistant plant due to the well-developed radicular system which, penetrating deep into the soil, absorbs the water from the deep layers, thus utilizing the reserves accumulated during rainy periods. Resistance to atmospheric drought is increased, compared to other crops, by the beetles covering the leaves and stem, preventing strong evaporation. The total amount of water consumption over the entire vegetation period is in our area between 300-450 mm, or 3000-4500 m3/ ha depending on the variety, meteorological regime of the year and the respective agropedological peculiarities. The highest amount of water consumption occurs during the formation of the capitulum and the filling of the grain. A particular influence on the percentage of seed oil has environmental conditions during the period of the capitulum formation and blooming. During this period, warm and humid weather contributes to the accumulation of a bigger amount of oil. Precipitations during the formation of floral primordia and blooming (May-June) as well as those during seed filling, have a favorable effect on the accumulation of oil. Apart from the hydro-thermal regime, the sun regime has a special influence on the production, the sunflower originating in the southern regions of the country. Light and moderate heat contribute to increasing the amount of seed oil and improving its quality. Excessive nebulosity contributes to the prolongation of vegetation, prevents oil formation and lowers its quality.