Avocado

What is an avocado?

The avocado is an evergreen tree of the laurel family with large, leathery leaves and fruit unlike any other: rich in oil, low in sugar, with a single large seed. It comes from southern Mexico and Central America, where it was cultivated long before the Spanish arrived. Today it is grown far beyond its homeland, and in dry regions its plantations are debated because of the water they consume.

Origin and growth

Avocado trees usually grow to about 9 metres, sometimes to 18 metres or more. Horticulture distinguishes three races that reflect their landscapes of origin. The Mexican race comes from the highlands and is the hardiest; its leaves smell of aniseed. The Guatemalan race comes from subtropical mountain regions. The West Indian race grows in the humid lowlands and needs a nearly tropical climate. Most of today's varieties, Hass included, combine Guatemalan and Mexican ancestry.

The fruit does not soften on the tree, apparently because of an inhibitor supplied through the stalk. It can therefore stay on the branch for weeks after reaching maturity and ripens in one to two weeks after picking.

Requirements

Cold. Morton gives about -4 °C for the Mexican race, and University of California extension gives the same critical temperature for Mexican varieties such as Mexicola. For Hass it lists about -1.7 °C. These values apply to mature trees; the longer the cold lasts, the greater the damage, and young trees are more vulnerable.

Water. High in summer, but the soil must never stay wet. Salty water damages the leaves and roots.

Soil. Deep, loose and well drained. The groundwater should lie at least about 90 centimetres down. Heavy, compacted soils favour root rot.

Wind. Wind dries out the flowers, disturbs pollination and causes young fruit to drop. Windbreaks are necessary in exposed sites.

Fruit, use and harvest

Avocados are harvested when fully grown and still firm, and they ripen in the kitchen. The fruit is eaten raw, as a spread or in salads. Its flesh is rich in fat, mostly monounsaturated. In a six-month randomised trial with 1,008 adults in the United States (Habitual Diet and Avocado Trial, 2022), one avocado a day did not reduce abdominal fat compared with the usual diet, but total and LDL cholesterol fell slightly; the authors attribute this partly to a generally better diet. For animals the avocado demands caution: according to the Merck Veterinary Manual, the persin in leaves, bark, seeds and fruit can cause mastitis and heart damage in goats, horses, rabbits and other species, and caged birds are particularly sensitive. Prunings do not belong in a pasture or a chicken run.

In the food forest

In a food forest the avocado is a canopy tree. It has a peculiarity that suits this way of growing: it drops a thick layer of leaves and grows its fine roots into that litter. A permanent cover of mulch imitates this natural situation, keeps the shallow roots cool and helps against root rot. In the first years young avocados are sensitive to strong sun; fast pioneers and nurse trees that give light shade and break the wind make the start easier. Because of the leaf toxicity, the avocado is a poor companion for grazing animals.

In the Mediterranean climate

Spain grows avocados on roughly 20,000 hectares, above all in Andalusia, with Málaga as the largest province. The Axarquía near Málaga shows the risks: during the drought of 2022 and 2023 irrigation from the La Viñuela reservoir was stopped, growers uprooted or cut back trees, and a study by the University of Bern reports avocado crop losses of up to 50 percent compared with the previous year. On Crete most Greek avocados grow around Chania, mainly Hass. For Sardinia, researchers in Sassari concluded in 1986, drawing on two decades of trials in Corsica, that avocados could be grown in the south of the island in warm microclimates, provided water is available. On a plantation near Orosei, about two hours north of Sa Medada, avocados have been bearing fruit for years.

The lesson from these places is consistent: the avocado can cope with Mediterranean heat if its roots are cool, its soil airy and its water secure. The avocado is not on the EU list of invasive alien species.

Propagation and care

Varieties are grafted onto seedling rootstocks; there are rootstocks bred for tolerance to root rot or salt. Seedlings bear later than grafted trees, according to Morton after four or five years, and rarely resemble their parent. Fallen leaves stay under the tree. Planting on a mound or a raised bed helps on heavier soils.

How Terra Humana understands it

At Sa Medada the avocado is a test of whether a thirsty tree can find its place in a planting built on soil cover, shade and stored water rather than on intensive irrigation. Its own falling leaves are part of the answer. Whether it fruits on the slope, and how much water it needs to do so, is what we want to learn.