Hazelnut tree is a plant that produces its fruits in late summer. It can provide great satisfaction whether cultivated in a home orchard or in a larger cultivation intended for sale. Hazelnuts, in fact, are highly valued in the market, both for fresh consumption and for processing. Today, we have decided to offer a comprehensive guide to the cultivation of this tree with ancient traditions in our country.
We will explore its various aspects, discuss the main varieties, and learn how and when planting should be done. Finally, we will become acquainted with the main cultivation techniques to ensure a healthy tree and organic hazelnuts.
Botanical Overview of Hazelnut Tree
The hazelnut tree is a fruit-bearing plant native to Asia Minor. It belongs to the family Betulaceae, genus Corylus. There are several species within this genus: Americana, Chinensis, Fargesii, Maxhima, Sieboldiana, and many more. The varieties cultivated in our country are mostly of the species Coryllus avellana.
Italy is the second-largest producer in the world for this fruit, following Turkey. It is a cultivar spread throughout the national territory, from plains to low mountains (1300-1500 m).
The most important regions for production are Campania, Lazio, Piedmont, Sicily, and Liguria.
Botanical Characteristics of the Hazelnut Tree
A characteristic of the hazelnut tree is its bushy growth habit. It typically reaches a height of about 4 meters, although in a free form, it can reach 7-8 meters. It has an extensive root system that reaches different depths depending on the soil type where it’s cultivated. It also has vigorous sucker growth. The trunk is thin and slender, often with a contorted shape.
Young branches are covered with short hair, only partially glandular. The bark of the tree is smooth and thin, brown-gray in color, marked by longitudinal grooves. The leaves are alternate on the branches, oval with serrated margins, and have a long petiole. The upper side is dark green with a slight hairiness, while the lower side is lighter and shows prominent veins.
Flowering and Pollination
The hazelnut tree is a monoecious plant, meaning male and female flowers are separate but present on the same plant.
Male flowers are grouped in a particular inflorescence called a catkin. This has the form of a pendant spike and is found in clusters in the axils of the leaves on the branches of the previous year.
Female flowers, on the other hand, are small buds that emit stigmas, a red tuft on the apex that receives pollen from male flowers. Cultivated hazelnut varieties are self-incompatible, meaning pollen is not accepted from male flowers of the same variety. In practical terms, cultivated varieties require a pollinator placed in the orchard to ensure proper pollination, fertilization, and fruiting. This operation can be avoided if there are other hazelnut trees nearby that match the characteristics of the variety you intend to cultivate.
The flowering of the tree occurs in winter, between December and March. The receptive period of female flowers lasts about a month and is between January and February. Pollination must occur during this time, followed by fertilization. This phase is critical and lasts longer compared to other fruit trees. Unfavorable seasonal weather can compromise the year’s production.
The Fruit and Phases of Hazelnut Tree Fruiting
The fruit of the hazelnut tree is the hazelnut (or filbert) consisting of a woody pericarp with a sweet and oily seed inside.
They usually grow on the tree in groups of 2-4 units. They start off light green and then turn brown.
The stages of fruit formation begin with fertilization, followed by enlargement. The hazelnut then begins to grow, transitioning from a spongy consistency to the milky phase of the seed, until the complete fruit forms.
Next are the stages of ripening, occurring when the fruit changes color and reaches the typical size of the variety.
Full maturity (and therefore harvesting) is achieved at the end of August and during September.
The hazelnut tree enters production from the 4th-5th year of age and reaches its peak productivity around 8-9 years. With proper pruning interventions, it can produce for up to 30 years!
Varieties and Pollinators of the Hazelnut Tree
Among the most widespread and cultivated hazelnut tree varieties in our country, we note:
- Tonda di Giffoni, a variety mainly cultivated in Campania, with medium-sized fruits, good yields, and excellent quality. Pollinators for this variety include Mortarella, Camponica, and Riccia di Talanico.
- Tonda Romana, a variety typical of the Viterbo area in Lazio. It has a medium to large-sized fruit, with good yields and excellent organoleptic characteristics. The pollinator is Nocchione.
- Tonda Gentile delle Langhe, a variety characteristic of Piedmont. It’s a high-quality variety with exceptional organoleptic characteristics. It adapts poorly to different climatic conditions from its place of origin. The pollinator for this cultivar is the Camponica variety.
Environment and Soil for Hazelnut Cultivation
For hazelnut cultivation, the tree prefers a climate without excessive seasonal fluctuations. It fears intense cold during the pollination phase, with temperatures dropping below -12°C. But it also fears excessive heat, with temperatures consistently exceeding 35°C. Therefore, the ideal environment is the hillside, where these adverse conditions are less likely to occur.
It prefers loose and cool soils, with a neutral pH (between 6.8 and 7.2). However, it’s a hardy cultivar that can adapt to clay soils, with care to avoid waterlogging that leads to root asphyxia and rot.
Before planting hazelnuts or establishing a hazelnut orchard, attention should be given to the presence of active lime in the soil, perhaps by conducting appropriate tests. An excess of lime limits the absorption capacity of microelements, particularly iron, causing issues like leaf yellowing (iron chlorosis).
Propagation of Hazelnut Trees
The simplest and most common technique to reproduce hazelnut trees is to use suckers from a coppice, known as the mother plant. Certified nurseries perform this operation by taking suckers from coppices and then rooting them in the nursery. At this point, the sucker is cut back to about thirty centimeters to promote root development. Usually, after two years, the small hazelnut plant is ready to be transferred to the open field. Great attention should be given to the choice of the nursery, which should offer plants from certified coppices, guaranteeing adequate phytosanitary conditions. Beware of those who offer hazelnut plants at a low price. It’s better to spend a little more money at this stage than to deal with diseases and issues unrelated to our activity.
Preparing the Soil for Hazelnut Orchard Planting
To establish a new planting, whether it’s a few plants or a full hazelnut orchard, the soil should be prepared during the summer months with deep plowing, usually through plowing. At this stage, it’s possible to carry out the basic fertilization of the soil using organic matter, such as organic manure from organic farms. The plowing should be at least 70 cm deep, after which surface cultivation can be done to refine the soil (subsoiling), using tools like a ripper.
Planting the Hazelnut Tree and Plant Spacing
The best time to plant young hazelnut trees is at the beginning of autumn, in early November. If an irrigation system is available, planting can also be done in early spring, right after the last frost. The holes to accommodate the young hazelnut plants are prepared either manually or with a small auger. They should have a diameter and depth of at least 40 cm. The hole with the plant inside is filled with soil, mixing in finer soil to encourage initial root growth. It’s advisable to set up a support with a wooden stake to protect the young plant from the elements. The choice of plant spacing (distance between trees) depends on various factors, with training form being a significant one. To facilitate subsequent operations (harvesting, pruning, soil management), a planting distance of 6×5 or 6×4 meters is preferred. The main training systems for the hazelnut orchard are:
- Bush form
- Bushy vase
- Standard tree
Fertilization and Irrigation of Hazelnut Trees
Fertilization and irrigation are two crucial aspects for having healthy and vigorous hazelnut trees. It’s good practice, at least once a year, to carry out fertilization with organic matter. For example, using worm humus or compost. In this case, in winter, spread the fertilizer around the base of the tree and lightly hoe the soil. As mentioned, hazelnut is a hardy plant, so in principle, it wouldn’t need supplementary irrigation. However, the ongoing drought affecting our country suggests considering an irrigation system, especially in the early years of the tree’s life. Prolonged water deficiencies cause a vegetative imbalance, reduce plant growth, flower bud differentiation, accentuate fruit drop, and ultimately reduce tree production. A surface drip system is an excellent solution.
Pruning of the Hazelnut Tree
Pruning hazelnut trees is a complex operation that takes place in different phases. Generally, pruning aims to establish a balance between productive and vegetative activity, limiting the occurrence of alternate bearing and premature filbert drop, similar to olive tree pruning. The best time to prune the hazelnut tree is during winter, between leaf fall and flowering.
Managing Weed Growth in the Hazelnut Orchard
It’s very important to keep the hazelnut orchard free from the presence of weeds. Weeds compete for nutrients with the plant and promote the presence of pests. In professional hazelnut orchards, periodic passes with a harrow are carried out. In a home orchard, a shallow hoeing is sufficient. As a cultivation technique, you can also opt for intercropping, which involves growing low grass around the orchard. This way, the structure of the topsoil remains intact. In organic farming, this technique is quite common but requires constant attention to maintain an acceptable level of intercropped grass.
Biological Pest Defense
There are many pests that threaten hazelnut cultivation. A detailed analysis deserves specific in-depth investigation. In this context, we provide general information. The main phytophagous insects that can compromise both the plant and the filbert are: the bud mite (Phytoptus avellanae), the green jewel beetle (Agrilus viridis), stink bugs (species Gonocerus acuteangulatus and Palomena prasina), and the nut weevil (Curculio nucum).
- Journal of the American Society for Horticultural Science: “Eastern Filbert Blight Susceptibility of American × European Hazelnut Progenies” – This article discusses the challenges and solutions related to the eastern filbert blight affecting European and american hazelnuts.
- Hortscience: “Eastern Filbert Blight-resistant Hazelnuts from Russia, Ukraine, and Poland” – This paper evaluates blight-resistant Hazelnuts from Russia, Ukraine, and Poland.
- Journal of the American Society for Horticultural Science: “Survey of cultivars for response to eastern blight inoculation” – This research surveys various hazelnut cultivars for their response to the eastern blight.
- Journal of the American Society for Horticultural Science: “Occurrence and inheritance of resistance to eastern blight in ‘Gasaway'” – The article discusses the genetic resistance of the ‘Gasaway’ hazelnut cultivar to the eastern blight.
- Acta Horticulturae: “Historical notes on filbert in Oregon” – This article provides historical insights into the cultivation and significance of filbert in Oregon.
- Oregon State University: “Eastern filbert blight in Oregon” – This paper discusses the challenges posed by the eastern filbert blight in Oregon and potential solutions.
- Journal of the American Society for Horticultural Science: “DNA markers linked to eastern filbert blight resistance from a selection from the Republic of Georgia” – This research explores genetic markers linked to blight resistance in hazelnuts sourced from the Republic of Georgia.