Spinach has a high nutrient requirement, so soil should be deep and fertile. It has a moderate salt tolerance, and its yield-loss salinity-threshold is 3-4 dS/m. On alkaline soils (pH >7.5), manganese deficiency can be expected. Irrigate regularly, or leaves collapse and the plant will wither. Spinach is best suited to cool climates with short days. Optimum soil temperatures for growth is 15-180C, and it is fairly resistant to frosts. Under warm conditions most spinach varieties will bolt, and high temperatures will cause the older leaves to yellow and die. Spinach forms a rosette of leaves that is harvested before flowering. It can be grown on a wide range of soils, but does best on light soils such as sandy loams or well-drained alluvial soils. It is highly sensitive to acid conditions and soil pH should be 6.5-7.5 for best results.