Hazelnut (Latin Corylus avellana) is a plant from the birch family (lat. Betulaceae) which also includes alder, hornbeam, hornbeam, ostriopsis and birch. It is also called hazelnut, kernel, kernel, hazel, coot and lišnjak. Although the exact origin is unknown, it is believed to have originated in Asia Minor, from where it spread throughout Europe and North America.
It is a Mediterranean culture that grows in the form of a deciduous shrub up to 4 m or a lower tree of 15 to 20 m. It develops roots rather shallowly, that is, at a depth of approximately 30 cm. Although it is shallow, the root is well developed and wide. Hazel leaves are alternate and simple. On the tree, they are mostly symmetrical and quite large, and they have double serrated edges.
Since hazel is a monoecious plant, male and female flowers grow on the same plant. The male flowers are grouped in 2 or 4 tassels that are 5 to 7 cm long, and the female flowers are barely noticeable because they are approximately 0.5 cm long. Male flowers form during autumn and open in early spring. As a result, the fringes spread and can be up to 20 cm long. On the other hand, the female flowers develop in dark red blooms as compact buds.
Hazel stands out because, unlike many other species, they don’t bloom in spring, but in winter. The flowering period lasts from December to March. Successful wind pollination in the third or fourth year results in hazel-brown fruits. The fruits are egg-shaped and have a hard woody shell. They are 1.5 to 2.5 cm long and contain one seed. The fruits ripen during August and September.
The hazel usually lives from 70 to 100 years, and can be seen in various thickets, on the edges of forests and in the zones of larch oak, beech, and ash. Apart from the lowlands, it can grow in areas up to 1800 m above sea level. Its natural habitat is the temperate zone of Europe and southwest Asia.
Types of hazel
In addition to the common or European hazel (lat. Corylus avellana) described in the introduction, it is possible to distinguish 10 other types of hazel, the most important of which are Caucasian, Istrian or Macedonian and bear hazel. Although gender Corylus includes a total of 11 species, approximately 300 varieties of hazelnut are known worldwide. Among the varieties in our area, the Roman and Hales varieties stand out, as well as high-quality industrial Italian varieties such as tonda di giffoni, tonda gentile delle langhe and tonda romana.
Caucasian hazel
The Caucasian or Pontic hazel (lat. Corylus pontica) can grow up to 4.5 m, so it is considered a medium-tall tree. It has round and heart-shaped leaves, and produces large fruits that are collected in groups of 6 or 8 pieces. The shell covers them completely, and can be whole or cut. This type of hazel is widespread in the area around the Black Sea in Asia Minor and the Caucasus.
Istrian or Macedonian hazel
The Istrian or Macedonian hazel (lat. Corylus maxima) is also called oblong hazel because it produces large and oblong fruits with a shell longer than the fruit. This hazel is most often grown in Croatia, especially in the continental parts, because it is resistant to low temperatures. It has a lush growth, but it resembles a bush more due to its growth in width.
Compared to other species, the Istrian hazel stands out because it ensures a regular and abundant harvest. Also, it is more resistant to pests compared to other species because it has a hard shell. The fruit weighs approximately 3.4 g.
Bear hazel
Bear hazel (lat. Corylus colurna) has a thick and broadly rounded crown, and it can grow up to 20 m. The trunk can be up to 100 cm in diameter. Yellowish and hairy young shoots later turn light gray, and the buds are quite large and dark brown in color.
The flowers are monoecious and unisexual, so the male flowers are drooping tassels and the female flowers are small buds with red threads. This type of hazel blossoms in March and April and produces a round fruit that is 1 to 2 cm in size. It is spread all over the world, from Asia Minor, the Caucasus, Afghanistan to the Balkans.
Roman hazel
Roman hazel is often grown in continental areas because it tolerates low temperatures well. It can be recognized by its appearance as a very lush tree with few shoots. The female flowers of this hazel begin to bloom already in November. It is a self-pollinating variety, and stands out as a good pollinator for other standard varieties.
It produces fairly large fruits that weigh approximately 3.10 g. Since it develops shoots rather poorly, it can be grown as a tree on its own roots. The only drawback of this variety is the possibility of an alternative crop, which can be alleviated with appropriate agricultural techniques.
Haleska hazel
Hale or Hale hazel is also resistant to low temperatures and is therefore good for planting in continental areas. This hazel has a medium lush tree that does not develop too many shoots. It is a self-fertilizing variety on which the flowers appear mid-late.
In order to ensure cross-fertilization between varieties, it is best to plant Haleska hazel with Roman and Istrian hazel. The fruits easily fall out of the shell, although the thick shell is firm. The fruits are brown with pronounced stripes and weigh approximately 3.4 g.
Tonda di giffoni
It is an Italian medium-growing variety that is characterized by regular fertility. Also, it becomes productive very early and produces high-quality fruits that are highly valued. Ripe fruits of this variety fall out of the sheath, so mechanical harvesting is possible.
Tonda gentile delle langhe
It is an Italian variety that is medium lush. This variety becomes productive early and maintains its productivity and produces fruits regularly. Ripe fruits of this variety fall out of the sheath, so mechanical harvesting is possible.
Tonda novel
It is an Italian variety that is medium lush. It gives birth regularly and gives its first fruits early. Ripe fruits also fall out of the sheath very easily and have a very pleasant taste and specific aroma.
Planting hazelnuts
For the successful cultivation of hazelnuts, it is necessary to know the appropriate methods of planting, as well as the conditions necessary for planting. This implies knowledge of planting time, soil characteristics, and appropriate temperature and habitat.
Planting time
Hazelnuts are usually planted in autumn, for example at the beginning of October, so that they can develop a root system before winter. However, it is possible to plant it at any other time of the year, it is only necessary to avoid high summer temperatures and winter frost.
Choosing the substrate for planting
Hazel is successfully grown on its own roots and as such can develop very well. Such a substrate is in accordance with the positions provided for growing vines. As for the cultivation position, hazel can grow in areas up to 1,500 or 1,800 m above sea level. However, in our continental areas, positions above 140 m that have the appropriate relief are ideal.
Planting seedlings
Before planting the seedling itself, it is first necessary to prepare the soil. Soil preparation involves leveling and deep plowing, but if it is plantation and intensive cultivation, it is good to check the quality of the soil and its chemical composition before these actions. If it is determined that the soil is too acidic or that there are not enough nutrients, such as potassium and phosphorus, then it is recommended to add mineral fertilizers over the entire surface of the soil.
If planting hazelnuts is done in autumn, deep plowing should be done earlier, i.e. in summer. Then the heat and occasional rains will have a positive effect on the crumbling of the soil. On the other hand, planting hazelnuts in spring is not recommended. For planting, only high-quality seedlings and hazelnut varieties that have the possibility of cross-fertilization are recommended. This means that it is not good to plant only one variety because it will not be able to fertilize itself.
When planting, it is necessary to combine an even number of rows of varieties. The planting distance depends on the characteristics of the soil, the lushness of the variety, the characteristics of the tree and the relief. Usually, seedlings are planted at a smaller distance of 4 x 3 m. If we are talking about sloping terrain, then the distance can be even smaller. Hazel develops a shallow root, so the seedlings should not be planted too deep. Too much depth can cause too slow growth.
Planting from seed
Planting hazelnuts from seeds involves a longer cultivation method than planting seedlings. The seeds can be obtained from harvested ripe hazelnuts. The ideal time to collect the seeds is when the shell can be easily removed from the hazelnut. Usually, a single hazelnut contains one seed inside, which is easiest to remove by hand.
The seeds should then be placed in a specific pot in which a mixture of pebbles and moist sand should be prepared. The seeds should be covered with this mixture and left in a shady place. Every 25-30 days, the seeds are poured, along with the sand, into another container to allow for ventilation. When the seeds show signs of germination, it is time to plant them in holes 5 to 7 cm deep.
Ground
Hazel does not have too many requirements in relation to the soil. Of course, fertile and calcareous soils suit it best, but it can also thrive on somewhat poorer soils. The most favorable soils for growing hazelnuts are those that are moderately deep and moderately moist. In addition, the soil should have a favorable structure, and the pH value should be from 5.0 to 8.0. Accordingly, skeletal soils and carbonate loams are distinguished as favorable soils.
Climate
In order for the hazel to give birth regularly and abundantly, it needs a sunny habitat. Namely, in the conditions of the shadows, they will bear fruit poorly. Also, hazel is sensitive to low temperatures. Accordingly, temperatures from -3 to -5 °C cause freezing of leaf buds at the time of the beginning of vegetation, and temperatures from -7 to -10 °C cause freezing of open female and male flowers. The flowers can freeze even while they are still unopened, at temperatures from -18 to -16 °C. Even lower temperatures of approximately -25 °C damage vegetative buds, and temperatures of -30 °C cause freezing of one-year shoots.
Hazelnut cultivation
Growing hazelnuts is not too demanding. Nevertheless, the success of the cultivation will increase the knowledge of the rules on combining cultures and reproduction, where the item on combining different varieties of hazelnut stands out. Also, for successful cultivation, it is important to water the plantations, as well as appropriate fertilization.
Matching cultures
It is good to sow oats, lupins and mustard near the hazel. In larger forests, hazel usually grows alongside hornbeam, oak, beech, ash and other types of trees.
When planting, it is necessary to plant several different varieties that can cross-fertilize each other. For example, one main variety or two main varieties and two or three pollinator varieties are most often planted. However, it is possible to have one main variety and one variety that will be a pollinator. In our areas, the Roman variety is usually combined as the main variety and the Istrian variety as the pollinator.
Watering
Hazel needs a moist habitat throughout the year. In relation to the amount of precipitation throughout the year, 800 to 1,200 mm of precipitation would be enough for hazel. The highest amount of precipitation is required during the growing season, which means in April and September. It is approximately from 350 to 500 mm. A slightly smaller amount, approximately 280 mm, is required during the later growing season until July.
Watering and irrigation is particularly important during planting and in the first years of hazelnut growth. If longer dry periods occur, then young plants need to be irrigated continuously. Also, irrigation is essential during fruiting if one wants to ensure a stable and high yield. In practice, it is evident that irrigation during June has a positive effect on the growth and size of fruits, and irrigation during August has a positive effect on the weight of the kernel.
It should be noted that the time of irrigation and the amount of water depend on the condition and age of the plantations, as well as on the type of land, habitat and land cultivation. For irrigation, it is easiest to use the underground and above-ground drip system.
Fertilization
If, during planting, it was determined that the soil does not have a sufficient amount of nutrients and ameliorative fertilization was carried out accordingly, the soil should only be fertilized with nitrogen in the first four years. Fertilization with nitrogen should then be done in early spring before vegetation in an area slightly wider than the perimeter of the canopy. In the first year, 0.5 kg is added, and in the second, 0.6 kg of mineral fertilizer. In the third year, the amount is increased to 0.8 kg, and in the fourth, 1 kg of mineral fertilizer should be added.
After the fourth year and up to the eighth year, hazel plantations should be fertilized with mineral complex NPK fertilizers together with KAN. Such fertilization should be carried out on the entire surface. Complex NPK fertilizer should be spread during autumn, and such feeding means adding approximately 20 kg/ha of phosphorus and 150 kg of potassium/ha. After that, in the spring, nitrogen is added in the amount of 100 kg, i.e. 350 kg/ha of KAN. After the eighth year, the hazel must be fertilized in the same way as after the fourth year. The only difference is that the quantities should be increased by approximately 35%.
Propagation
Hazel can be propagated in several ways, for example by seeds, shoots, cuttings, grafting and grafting. Seed propagation, i.e. generative propagation, is mostly carried out in scientific institutions for the purpose of creating new varieties and during the production of grafting media. Accordingly, it is recommended to propagate the hazel by cuttings and shoots, as these are the simplest and cheapest ways.
Propagation by cuttings is done during autumn. It is necessary to take 20 cm long cuttings and keep them in moist sand at a temperature of 10 °C during the winter. When spring comes, the cuttings are planted in a moist substrate and planted in a certain sheltered place until they are completely strong. As for propagation by laying, it takes place on one-year saplings that are simply laid in the ground and then covered with earth.
It is always necessary to plant hazelnuts of different varieties in the orchard because one variety cannot fertilize itself. Another variety is needed to be a pollinator. As the hazel blossoms in winter, it is pollinated by the wind and blooms for a very long time. In order to enable safe fertilization, at least three cross-fertilizing varieties are always planted in plantations.
Maintenance and care
Maintenance and care of hazelnuts include the care of tilling the soil and maintaining the seedlings. Particularly noteworthy is the measure of pruning and shaping, which directly affects the growing form of the hazel, as well as its effectiveness in terms of giving birth.
Plantation maintenance
Maintenance of plantations first involves inter-row tillage, and then hoeing of seedlings during the first and second year of cultivation and the use of soil herbicides. After approximately the sixth year of cultivation, it is possible to shape the lawn in the spaces between the rows. This especially applies to areas that have a sufficient amount of rain during the summer months. Shaping the lawn includes regular mulching and an appropriate form of fertilization. Also, it is necessary to provide light to the hazel because the light will have a positive effect on the number of fruits.
Pruning and shaping
Four basic cultivation forms are known for hazel. It is about the shape of a natural bush, a bushy vase, an ordinary vase and a pyramid. The shape that is most often used is the bushy vase shape, which is a shape without a trunk. The cultivation form is formed in the first years of the tree’s life according to the rule that there are four basic branches from which secondary skeletal branches develop.
Secondary skeletal branches should be spaced approximately 50 cm apart. In this way, natural growth conditions will be ensured and light will reach all the branches. This is extremely important because illuminated branches yield 2 to 3 times more than branches in the shade.
Harvesting hazelnuts
The hazel tree begins to bear fruit in the third or fourth year. However, it does not yet give birth to a full crop. It is achieved in the seventh or eighth year. When it comes to the full fruit of one hazel tree, it means from 8 to 12 kg of fruit, whereby approximately 50% of the fruit is related to the shell. The yield is affected by the cultivation form, planting density and the age of the plant, but it is usually 2.2 – 3.6 t/ha.
Harvesting of hazelnuts usually takes place from the end of July until the beginning of October. Of course, the harvest time normally depends on the varieties and the area of cultivation. It is necessary to monitor when the fruits are ripe, which is when they change color from green to yellow-brown and when they easily fall out of the casing. Harvesting can be made difficult by the fact that in some varieties the fruits are difficult to separate from the casing, and sometimes not all the fruits ripen at the same time. In addition to fruits, it is possible to harvest tassels, which can then be used to make flour.
Drying hazelnuts
Harvested fruits have a shell and as such contain approximately 30 to 35% water. They need to be dried at a temperature of 32 to 34 °C in order to reduce the water content to 8-10% and to make it possible to separate the fruits from the shell. The drying time usually lasts from 6 to 8 days and the fruits should be mixed often.
If, during drying, a shell remains on some fruits, such fruits must be stored in a closed space in a layer of approximately 30 cm. They should be stored in this way for 10 to 12 days, and they must be constantly stirred in order to speed up drying and to separate the casing.
Storage of hazelnuts
Hazelnuts will last the longest if they are kept in their shells and tightly sealed in a plastic container or bag. Well-dried hazelnuts can be stored for up to 2 or 3 years, but it is usually the case that after a year they start to lose weight and color. Accordingly, it is recommended to keep them for up to one year. A dry and lighted room is necessary for storage. Wet rooms should be avoided because in such conditions the hazelnuts will quickly deteriorate and lose weight and quality.
In such a suitable space, the hazelnuts should be distributed in thin layers and should be mixed occasionally. Also, it is recommended to occasionally burn sulfur in the room in order to destroy certain fungi, but also to preserve quicklime, which reduces the humidity in the room. An electric fan can also contribute to humidity regulation.
Diseases
For the successful cultivation of hazelnuts, it is necessary to know the threats that can harm its development. It is possible to distinguish several of the most common diseases and pests and the appropriate rules of procedure for their control.
There are several of the most common diseases that attack hazel. These are hazel brown rot, hazelnut core rot, hazel powdery mildew and hazel bacteriosis. Bacterial hazel blight and bacterial hazel cancer are distinguished from hazel bacterioses.
Brown rot of hazelnut fruit
It is a disease caused by fungi from the genus Monilia spp. The disease occurs on the fruits, and is recognized by irregular light brown or maroon spots on the skin of the fruit. These spots spread and affect almost the entire surface of the fruit. If the fruits are attacked early, it is very common that they fall off. They can rarely stay on the branch until late autumn. The collection and burning of rotten fruits stands out as a protection measure. In addition, it is good to plow infected fruits.
Since mushrooms from the genus Monilia cannot penetrate undamaged tissue, protection measures against pests that damage the fruit are also important. It is then possible to apply a specific fungicide. Protection is usually carried out when the first fruit damage is noticed, which is usually at the end of May and the beginning of June.
Hazelnut kernel rot
Hazelnut core rot is a common disease in our areas caused by fungi Nematospora coryli, and is associated with the appearance of bed bugs. The disease attacks the fruits, which after infection begin to turn yellow from the top, and then that part of the shell at the top changes color to brown. Accordingly, changes also occur inside the fruit, and they depend on the stage of development in which the infection occurred.
If the bites of bedbugs occurred early, approximately in May and June when the fruit core is just beginning to form, then the core no longer develops, but turns black, rots and dries up and remains empty. Then brown drops appear on the inside of the shell. If it is a question of non-parasitic factors that caused the absence of core and seed formation, then brown drops do not occur.
On the other hand, if bugs bite the fruit when the core is already formed inside, then the core becomes brown or yellow and has an unpleasant sour taste. In this way, the core of the fruit is completely destroyed and loses all value. The inside of the fruit can be infected with this disease, and no changes can be noticed on the surface of the fruit.
As for protection measures against hazelnut kernel rot, they relate to reducing the possibility of fruit damage, as it has been shown that infections develop through wounds. Accordingly, it is necessary to control bugs and other pests that can damage the fruit.
Hazel powdery mildew
Hazel powdery mildew is a disease that attacks the leaves and is caused by a fungus Phyllactinia guttata. It usually occurs from mid-August until October. First of all, white dirty zones appear on the upper side of the leaf and the leaf can become necrotic in these affected areas. On the other hand, an ashy coating appears on the reverse side of the leaf, which is loose and spreads quickly.
Thus, light brown cleistothecia are formed in the mycelial network, which then turn black. If the attack is severe, the entire leaf may dry up. This disease is favored by humidity of 70 to 80%. In relation to protection measures, it is possible to use fungicides based on sulfur, fenarimol, penconazole, meptildinokap and strobilurun.
Bacteriosis of hazelnuts
Two bacterioses can appear on hazel. One is bacterial hazel blight and the other is bacterial hazel canker. Both bacterioses attack all parts of the plant, and are recognized as dark spots. They cause canker sores on the branches, and bacterial discharge appears in the infected places. The disease is intense in periods of humidity and rain. It acts on the plant so that its individual parts dry out, and sometimes whole trees dry out.
As for protective measures, it is necessary to remove the infected parts of the plant, i.e. the branches, because this can significantly reduce the infection. In addition, copper-based fungicides can be applied at the beginning of vegetation, i.e. at the time of bud opening. If the need for another treatment is noticed, it can be carried out at the end of summer or the beginning of autumn, but then it is necessary to apply an organic fungicide based on captan, metiram and mancozeb. It should be noted that there are no registered fungicides for these bacterioses in Croatia so far.
Pests
In addition to diseases, hazel can also be attacked by certain pests. The hazel mite and hazel weevil are the most common and attack the buds and fruits of the hazel. It is possible to properly protect hazelnut plantations with appropriate measures.
Hazelnut mite
The hazelnut mite is a very common pest of hazelnuts in Croatia, and especially threatens hazelnut plantations in Istria. These are very tiny white mites that attack the buds. They most often occur during colder and wetter springs, and multiply during autumn and winter. This pest has several generations per year.
It causes swelling of the buds, which consequently do not open. If they do open, then deformed leaves develop from them, which then dry up. As a protective measure, it is recommended to treat with endosulfan, sulfur agents or acaricides, when 3 to 5 new buds form on the new summer growth. If there is more damage, the treatment can then be repeated in 15 days.
Flashpoint
Along with the hazel mite, the hazel weevil is the most common hazel pest that causes “worminess” and fruit drop. It is a beetle insect that is 6 to 9 mm in size. It has a red-brown appearance and is covered with yellow-gray hairs. It can be recognized by its elongated head and long but narrow snout, and the mouth is located on top of the snout. In native plantations, it can cause a total of 10 to 40% damage. In the spring, this pest pupates so that adult beetles emerge in May. As a protective measure, the use of preparations for protection against bacteriosis is recommended.
Use of hazelnut
Hazelnuts, hazelnuts, are extremely popular in cooking, but also in medicine. As nuts, hazelnuts are highly valued because they contain many useful ingredients for human health, and they can be consumed in different ways and combined in different dishes.
Hazel in medicine
Hazelnuts are a very energy-rich food that belongs to the group of nuts. It contains many valuable vitamins such as C, E and B and minerals such as magnesium, iron, phosphorus, potassium, calcium, zinc and iodine. In addition to vitamins and minerals, hazelnuts also contain proteins and dietary fibers.
Thanks to the content of oleic fatty acid, hazelnuts help lower blood pressure. This acid also has a positive effect on overall brain activity and memory. In addition, it is possible to find omega-3 fatty acids in hazelnuts. Due to the high concentration of vitamin E, hazelnuts stand out as antioxidants. They influence the improvement of immunity and health.
Crushed hazelnut can be combined with honey and as such preparation can be used against cough. It is also possible to use hazelnut oil for problematic and oily skin. In addition, it also helps with scars, stretch marks or varicose veins, so it is a common ingredient in many cosmetic products.
Hazelnut in cooking
Hazelnuts can be consumed raw or fried and as an addition to various dishes. They are a common ingredient in many cakes and pies, but they can also be combined in various soups, pastas, fillings, sauces and ice creams. If you want to consume them fried, then it is enough to lightly fry them in a pan without adding oil.
Hazelnuts go well with coffee, honey and oatmeal. In Spain, fried and ground hazelnuts are mixed with honey, which represents an autochthonous delicacy there that is consumed with coffee or during the traditional welcome of guests. In addition, many combinations of hazelnuts and, for example, asparagus, beets, parsley, cheese, tomatoes in the form of salads or sauces are possible for starters.
Also, ground hazelnuts can replace flour in cakes, where they are usually combined with butter, chocolate, cocoa, eggs and sugar. In general, hazelnuts are an excellent choice for a quick snack because they contain a sufficient amount of calories. Since hazelnut, like other nuts, can be an allergen, it should be avoided if there is a suspicion of an allergy or confirmation of an allergy.
History
The origin of hazelnut cannot be determined with certainty. Some believe that the common hazel originates from Greenland, while others point out that the hazel originates from Asia Minor and East Asia. It is believed that the cultivation of hazelnuts began 2000 years ago and that the difference between tame and wild hazelnuts was first noticed by the ancient Greeks and Romans.
Specifically, Theophrastus, Pliny and Coton the Elder were the first to write down notes about the hazel. Their records bear witness to the fact that the tame hazel was brought from Asia Minor to Greece and that it came from there to Italy and to Silicon. As for Croatia, the first significant expansion of hazelnut cultivation was from 1983 to 1986, when 230 ha of hazelnut plantations were planted in Orahovica.
Interesting things
Some varieties of hazel can grow up to 20 m in height, and the crown of the tree is generally as wide as the height of the tree itself. Hazel is considered to be a tree of wisdom and knowledge. Related to this is the Celtic belief that people born from August 5 to September 1 are extremely smart. Such people, according to belief, have a sharp mind, therefore they are successful in observation and writing skills. Also, they are excellent organizers and have artistic tendencies. It is not uncommon for them to appear as cold and reserved people, but in close relationships they are very sincere and caring.
According to Irish folk belief, a fairy who loved poetry once hid in a hazel tree. Furthermore, the god of medicine and trade, Mercury, was depicted with a hazel branch around which there are two snakes. It is believed that witches once used a hazel stick to drive out the devil from bewitched people, and with the same hazel stick, water was searched for and the place to dig a well was determined. Hazelnuts are also said to be a symbol of peace, so in some Italian villages it is a common custom to offer guests hazelnuts as a sign of friendship.
The importance of hazel was recognized in turning, so hazel was used as a wood for making various sticks, umbrella holders, fences, floors, barrels, etc. It is interesting that there are many places in Croatia that were named after hazel and hazel. Some of them are Kordunski Ljeskovac, Plitivčki Ljeskovac, Hrvatski Leskovac, Leskova Draga, Lešće, Lešnica, educational trail Leska, etc.
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