The subtropical species needs a climate without frost and with little wind. High winds reduce the humidity, dehydrate the flowers, and affect pollination. When even a mild frost occurs, premature fruit drop may occur, although the 'Hass' cultivar can tolerate temperatures down to −1 °C. Several cold-hardy varieties are planted in the region of Gainesville, Florida, which survive temperatures as low as −6.5 °C (20 °F) with only minor leaf damage. The trees also need well-aerated soils, ideally more than 1 m deep. According to information published by the Water Footprint Network, it takes an average of approximately 70 litres (18 US gal) of applied fresh ground or surface water, not including rainfall or natural moisture in the soil, to grow one avocado. However, the amount of water needed depends on where it is grown; for example, in the main avocado-growing region of Chile, about 320 litres (85 US gal) of applied water are needed to grow one avocado.[30] Yield is reduced when the irrigation water is highly saline. Like the banana, the avocado is a climacteric fruit, which matures on the tree, but ripens off the tree. Avocados must be mature to ripen properly. Avocados that fall off the tree ripen on the ground. Generally, the fruit is picked once it reaches maturity; Mexican growers pick 'Hass' avocados when they have more than 23% dry matter, and other producing countries have similar standards. Once picked, avocados ripen in one to two weeks (depending on the cultivar) at room temperature (faster if stored with other fruits such as apples or bananas, because of the influence of ethylene gas). In some cases, avocados can be left on the tree for several months,
