Native to the eastern Mediterranean to Pakistan, the sweet almond tree (Prunus dulcis) was planted across the Mediterranean, including Spain, by the Egyptians, Greeks and Romans. Today, Spain is the second leading producer of almonds in the world, according to the Food and Agriculture Organization's commodity statistics for 2007. In the United States, California produces five times the tonnage of almond nuts than Spain. Ironically, it was Spanish missionaries that introduced sweet almond trees into California at Santa Barbara in the 18th century, according to the University of Georgia.
Spanish almond trees grow with an upright, V-shaped habit with spreading branches. In the wild, the trees can reach nearly 33 feet tall and wide with a dome-like canopy, but those grown in commercial orchards today are typically kept at a height and spread between 10 and 15 feet, according to the University of Georgia. Trees can live well over 50 years of age.
In late winter to very early spring, the bare branches on Spanish almond trees are lined with thousands of small, fragrant, five-petaled flowers. The petals are white to pale pink and are most readily pollinated by bees. Since the blossoms occur so early in the growing season, late frosts or cool, wet weather can damage and diminish the numbers of flowers on trees.
After flowering wanes, the green leaves emerge and cloak the branches. Each blade matures 3 to 5 inches long and looks like a narrow lance or slightly oval line with point tip and teethed edges. The leaf blade is only one-third to one-quarter wide when compared to its length. The foliage falls away in autumn.
Flowers successfully pollinated in spring develop into fruits called drupes, much like those of peach, plum and apricot trees. The Spanish almond's fruit lacks the juicy flesh. As the almond fruit matures, the outer layer remains dry and leathery, a hull, that cracks open in very late summer when ripe. Inside this hull is the endocarp, or "shell" or "kernel," of the almond nut. Breaking open this shell reveals the seed, which is what humans eat as the "nut." The seed contains a cyanide-producing compound called amygdalin that provides the nut with its distinctive odor and flavor, according to Beryl Simpson and Molly Ogorzaly in "Economic Botany: Plants in Our World."
Native to regions with a cool but mild winter and long, hot, arid summer, Spanish almond trees prosper where such a growing environment dominates. Grow them in U.S. Department of Agriculture Hardiness Zones 5 through 8. Using Sunset climate zones, the almond tree is best grown in Zones 2b through 3b, 8 through 10, 12 through 16, 19 through 21. They are less reliably hardy in zones 29 and 30 and the western parts of zones 33 and 35.