The avocado (Persea americana) is a fruit plant native to Central America. It has been cultivated with excellent results in our country for some years. Being a tropical plant, it prefers a warm climate, making it ideal for cultivation in the southern regions, especially in Sicily. This is where most of the national production is concentrated. However, there are several varieties of avocados, some more resistant to cold, allowing cultivation in other areas. The key is to follow the right cultivation practices and wisely choose the suitable variety.
In this article, we illustrate the botanical characteristics of avocados, focusing on the varietal orientation. Additionally, we explore organic cultivation techniques to grow healthy and thriving avocado plants in the family orchard.
Origins of Avocado
The avocado is a fruit tree belonging to the botanical family of Lauraceae. Another tree familiar to this same family is laurel.
The origin of the avocado is believed to be in southern Mexico. It was cultivated throughout Central America in pre-Columbian times before the arrival of Europeans. The primary area of distribution was between the Rio Grande (now Colorado) and Peru. Today, avocados are intensively cultivated not only in America but also in many areas worldwide. Some production areas include Polynesia, the Philippines, Australia, New Zealand, Madagascar, Mauritius, Madeira Island, the Canary Islands, Algeria, South Africa, southern Spain, southern France, Sicily, Crete, Israel, and Egypt.
Botanical Classification of Avocado and the Different Species
The botanical classification of avocado is complex. However, we’ll outline it in broad strokes. There are three different species (or races) of this fruit: Mexican, Guatemalan, and Antillean. Today, both pure varieties and hybrids are cultivated, exhibiting different characteristics from the main species. The varieties most commonly grown here are hybrids of Mexican and Guatemalan species, called Fuerte and Hass.
The varieties of Mexican avocado species tolerate our climates better. Mature trees withstand temperatures down to -5 °C without damage. The main commercial varieties include Zutano, Bacon, and Shephard.
Guatemalan species, however, come from tropical highlands and require a cooler tropical climate without extremes of humidity and temperature. These trees can withstand temperatures down to -2 °C. Varieties such as Gwen and Reed belong to this group.
The group of Antillean avocados originated in the moist, low lands of tropical Central America. This group is more tolerant of saline soils and water. However, they are the least cold-resistant species, making them less suitable for our climates.
Characteristics of the Avocado Tree
The avocado is an evergreen tree, with a very dense canopy and an appealing appearance. It can reach heights exceeding 20 m but usually has more moderate dimensions, thanks to pruning interventions. It grows rapidly, reaching the size of a 10-year-old orange tree in 3-4 years. Vegetative growth is intense in summer but slows significantly in autumn and winter. Although an evergreen, it renews its foliage progressively in spring. A leaf lives for about 2 years, much like the Japanese medlar. Avocado leaves are alternately arranged on branches, glossy, elliptical in shape, dark green with lighter veins. The Antillean varieties have no scent, while the Guatemalan and Mexican varieties have a distinct anise odor. They are also rich in essential oils and have medicinal uses. Leaves that fall to renew should be left in piles at the tree’s base. Their slow degradation acts as natural fertilizer.
Avocado Flowers and Blooming
The flowering of the avocado plant is unique and determines the cultivar’s productivity. The flowers are hermaphroditic, having both male and female sexual organs. However, self-pollination is difficult. This genetic flaw is naturally corrected due to the existence of two different types of floral biology. Usually, flowering occurs over 2 days, with differences in the morning and evening. Avocado plants are distinguished in Groups A and B:
- In Group A, the flowers have pistil receptivity in the morning of the first day, acting as female flowers. The issue is that they also have bent anthers, preventing pollen fertilization. However, in the afternoon of the second day, they behave as male flowers.
- In varieties of Group B, the opposite occurs. Therefore, to achieve fertilization and production, it’s essential to have simultaneous presence of plants from both groups (cross-pollination).
Even in a family orchard, it’s necessary to have at least two plants, enabling the overlap of flowering stages.
Fortunately, the group membership of the main varieties listed earlier is already known.
An excellent combination, for example, is between the Hass variety (Group A) and the Fuerte variety (Group B).
Other factors influencing proper flower fertilization and good productivity are:
- Presence of pollinating insects, especially bees
- Day temperatures above 10 °C, for at least 3 consecutive days during the flowering period.
Flowering occurs in late spring, so there should be no issues with insect presence or temperatures.
Regarding avocado fruits, differences exist based on the species. Guatemalan species produce medium-sized fruits, oval-shaped, similar to pears. They are dark green when fully ripe. Mexican variety fruits are smaller, weighing about 170 g. They have very thin skin and are almost glossy black when fully ripe. In general, the pulp of avocado fruits is intensely green near the skin and more yellow near the seed. The pulp yields oil that offers many benefits to the skin and hair (several formulations are available here). The seed inside the fruit is single, large, oval-shaped, and inedible. When freshly harvested, the fruit has firm pulp, but it softens to a buttery consistency. Hence, the fruit continues ripening even after being picked. This favors keeping the fruits on the tree without spoilage. However, it’s worth noting that fruits in the ripening phase on the tree are very sensitive to wind. Sometimes, wind action can cause abrasions. Harvesting starts in autumn, in October and November for early varieties. Late varieties can ripen their fruits until early spring.
One of the peculiarities of avocado is its ease of reproduction by seed. Simply place it upside down in a glass of water, secure it with toothpicks to keep it in the right position, and wait a few days. The seed opens, and a root starts forming. Then, it can be placed in the soil and start growing in a pot. In our opinion, this technique is suitable if you want to grow avocados in a pot or for ornamental purposes in the orchard. However, the problem in achieving productive plants using this reproduction system is linked to choosing the variety (often unknown starting from the fruit). This leads to issues in cross-pollinating plants from different floral biology groups, as explained earlier. To plant avocado trees and ensure certainty in fruit quality, it’s best to turn to specialized nurseries. Here, certified plants, already grafted, of at least two different compatible varieties can be purchased. With the increasing popularity of this cultivar, one can find plants at reasonable prices, usually sold in special plant containers. The best time to plant an avocado tree is the beginning of spring, with the risk of frost behind. Adult trees, being large both in height and volume, need ample planting space. We recommend at least 6 m between plants and 8 m between rows.
Avocado is a tropical plant, but as we’ve seen, there are varieties that adapt well to our climate. However, it’s not advisable to cultivate avocados in areas with long, cold winters, continuous frost, and temperatures dropping below -5 °C. Southern regions have an ideal climate for avocado cultivation. Still, protection of plants from frost in the colder months is necessary. As for the position in the orchard, it’s best to choose a sunny yet sheltered location from strong winds.
Soil and Irrigation
The ideal soil type for avocado cultivation is loose, cool soil. It’s essential that it also has excellent water drainage, good fertility, and a neutral pH. It’s not a plant that adapts to challenging soils, such as clayey and compacted soils. Water drainage prevents the occurrence of fungal diseases and root rot. Avocado needs continuous watering during the hot months. In summer, the plant has vigorous growth but requires consistently moist soil. In other seasons, irrigation needs decrease (which, of course, depends on precipitation volume).
Cultural Care, Mulching, and Weed Control
The avocado tree has a shallow and expansive root system. To favor root health, it’s advisable to create a layer of natural mulch around its canopy. This will help maintain soil moisture. The resulting superficial root development will simultaneously prevent the presence of weeds around the plant. Another positive factor of mulching is the protection it provides the root system from direct sunlight. The best soil management method between rows is permanent vegetation cover, with periodic cutting of herbaceous species (preferably legumes) used for covering. Any form of tillage, even superficial, should be absolutely avoided. Vegetation cover between rows and mulching around the tree also nourish the plant, eliminating the need for additional organic amendments.
As previously emphasized, the avocado is a fast-growing fruit tree. In nature, in tropical environments, it grows freely and lushly, reaching significant sizes. In domestic settings, it’s advisable to intervene with pruning to obtain more compact and easily manageable plants during harvesting. Training pruning in the initial years is therefore fundamental. Once the plant has grown, intervening becomes more challenging. The goal of this type of pruning is to encourage the formation of a single main trunk and several main branches by maintaining lateral buds. If the nursery plant isn’t already shaped, pruning should occur after planting and, for the following 2 years, at the beginning of spring. Once the tree framework is established, interventions will be limited to thinning out the vegetation. During this phase, it’s sufficient to remove dry, damaged, or crossing internal parts. Avocado wood is highly sensitive to wounds caused by pruning cuts. Hence, after cutting, it’s recommended to treat with healing products, especially propolis.
Avocado is highly susceptible to the presence of a fungal pathogen: Phytophthora cinnamomi. This belongs to the same family as tomato late blight, Phytophthora infestans. It’s a fungus that attacks the roots of woody plants, causing them to rot, especially if very thin. The rot caused by the pathogen easily extends to the base of the stem, with brownish lesions in the wood. The leaves of affected plants become chlorotic and wilt, and in severe cases, the plant risks dying. Other symptoms include: decline, reduced fruit size, gumming, fruit and plant collar rot. Infected plants may collapse rapidly. However, sometimes they survive for several years, becoming asymptomatic but potentially infectious for healthy plants. Biological defense against this disease is implemented through adequate agronomic practices that don’t stress the plant. First and foremost, water stagnation, the primary cause of fungal spread, must be avoided at all costs. Additionally, water stress, i.e., excessive watering after dry periods, should be avoided. Always remember that plants need little water but given consistently. Excessive nitrogen fertilization is another danger. Regarding animal pests, the avocado is usually less sensitive compared to our other fruit-bearing plants. Being of tropical origin, it’s accustomed to numerous pests.