The almond tree, Prunus dulcis, is a temperate fruit crop that requires a highly predictable Mediterranean climate pattern for successful production. This commercially significant plant relies on a narrow set of seasonal temperature and moisture needs. Its cultivation is largely confined to specific geographical regions that can deliver the necessary environmental cues throughout the year. The crop’s yearly cycle depends on a precise sequence of winter chill, a mild spring, a hot summer, and a consistent water supply.
The Essential Winter Chill Period
The almond tree must enter a period of deep rest, or dormancy, during the winter months. This dormancy is broken only by the accumulation of sufficient “chilling hours,” which is the total time buds are exposed to temperatures generally between 32°F and 45°F (0°C and 7.2°C). This cold period is necessary for the tree to prepare for spring growth, ensuring a uniform and healthy bloom once warmer temperatures return.
The required accumulation of chill varies widely, but many commercial varieties need 200 to 400 hours below the threshold temperature. If a winter is too mild and the trees do not receive enough chilling hours, the dormancy period is not fully satisfied. This results in a poor quality bloom that is delayed, uneven, and sparse, severely reducing the number of nuts produced.
Delicate Spring Bloom and Frost Vulnerability
The transition from winter dormancy to flowering is a period of high climatic sensitivity, typically occurring from mid-February to March in major growing regions. Ideal conditions for successful bloom involve mild, dry, and windless weather, which maximizes honeybee activity for cross-pollination. Bees are most active and effective when temperatures are between 55°F and 100°F.
The developing almond blossoms are vulnerable to frost damage. While pink buds can tolerate temperatures down to about 25°F, an open flower is damaged when temperatures drop below 29°F (-1.7°C). A single hard freeze at full bloom, where temperatures fall below 28°F, can cause significant losses by killing the reproductive parts of the flower. Cold and wet weather during this time also hinders bee activity and promotes fungal and bacterial diseases, diminishing the potential crop set.
Summer Heat and Maturation Requirements
Following the spring bloom, the almond requires a long, hot, and dry summer to properly mature the kernel inside the hull. Sustained high temperatures are necessary for the nut to develop its characteristic oil content, size, and flavor. The timing of the hull split—when the outer husk opens to expose the shell—is largely determined by temperature accumulation in the first 90 days after bloom.
Warmer conditions lead to an earlier hull split, typically occurring around late June through early July. Low atmospheric humidity is necessary during the final maturation phase to prevent the growth of fungal pathogens like hull rot. The dry, hot climate allows the hull to dry and open completely, which is essential for mechanical harvesting.
Water Requirements and Regional Adaptation
Despite thriving in a dry-summer climate, the almond tree is not drought-tolerant during its peak growing stages and requires a significant, consistent supply of water. To achieve optimal yield and nut quality, a mature almond tree needs between 40 and 58 inches of water annually. This high water demand means commercial cultivation is concentrated in regions that offer the ideal seasonal climate but also have access to reliable irrigation.
In areas like California, Australia, and Mediterranean countries, orchards rely heavily on managed irrigation. They often use micro-irrigation systems, such as drip emitters, to apply water directly to the root zone. Water-intensive farming in naturally arid regions presents a challenge, especially when dry heat leads to water scarcity. Growers must carefully time irrigation to key growth periods, as water stress during early fruit development can significantly reduce the final crop size.