Olive Tree

Olive (lat. Olea europea L.) is a plant that belongs to the botanical family Oleaceae and grows in the form of an evergreen branched shrub or tree. On average, it can grow from 3 to 13 m (10 to 42 ft) in height.

Olive fruits grow on a twisted and gnarled trunk with branches extending and forming an irregular canopy. Its root is well developed and branched with smooth and gray bark. As the tree matures, the bark becomes rough, slightly cracked, and covered with dark scales. It also has well-developed buds covered with gray hairs.

Olive leaves are elongated, green, and depending on the species, can grow between 3 to 10 cm (1.2 to 3.9 in) and be approximately 2 cm (0.8 in) wide. The leaves grow on short pedicles with a pointy top.

The olive tree blooms with beautiful white flowers arranged in inflorescences. Flowering occurs during April and May, and the flowers are often pollinated by the bees. The olive is cultivated for its fleshy ovoid fruit. The size of the fruit depends on the olive strain, but the average size is 1 to 3 cm (0.4 to 1.18 in) long and up to 2 cm (1 in) wide with a pit inside.

Olives begin to ripen in early fall, in September and October. When the plant starts to germinate, the fruit becomes green and as it ripens the color changes to dark green, brown, dark blue and black. Olives are usually cultivated in Mediterranean regions.

Olive Varieties

There are over 40 species of olives in the world, but only one species in Europe that is suitable for cultivation: Olea europaea ssp. europaea. Other varieties can be found in Asia and Africa, and are not of major importance in agriculture.

Choosing the right olive tree depends on the geographical area of cultivation and its climatic conditions. Before choosing, it is important to determine whether olives will be cultivated inland, on islands or along the coast, as well as to define the climate conditions of those areas. Don’t dismiss the importance of the soil type and the method of cultivation.

Although this is no less important, the olive tree that will be planted is mostly selected according to the harvesting method: hand-harvesting or machine harvesting.

Since the cost of olive production is largely determined by the cost of harvesting (approx. 70%), it is recommended that you give preference to varieties whose harvest will be easy and there will be no need for bigger expenses.

Although olives can withstand harsh growing conditions (low and high temperatures), they still need high quality soil. There are also some varieties that need more water and moisture than others. Therefore, before you decide on which type of olive tree to plant, take into consideration that quality irrigation is required if you plan to cultivate olives for mass production.

When choosing the right olive species, check what type of soil exists in your area and define the expected yield for certain species. In addition to the above, it is important to know if you grow self-pollinating species, when they bloom and who are the pollinators.

It is difficult to meet all the conditions and choose the variety that will achieve the best yield in an area, but you should try to satisfy most of the conditions we mentioned above. When growing young plantations, it is recommended to plant at least three species that blossom at the same time, so they can pollinate each other. The olive grove should have a minimum of 10% pollinators, and each olive species must be planted at least 40 meters away from the other for successful pollination.

Olives can be cultivated for oil production, production of table olives and production of table olives and oils.

Planting olive trees

Before planting, it is necessary to determine the distance between the rows and the direction of planting. The general distance between planting olives should be between 5 to 8 meters (16.40 to 26.24 feet), while the most common distance is 7 meters (22.96 feet). It is recommended to plant the trees in a north-south direction and to adjust the rows according to wind direction and strength.

Shapes of olive groves:

• rectangle - faster shading of the canopy at a smaller planting distance
• square - easy to do soil tillage
• triangle - better sun exposure and easier machine movement

Before planting, it is necessary to prepare the soil tillage 3 to 4 months before planting the first seedlings. Also, to begin with, it is necessary to perform a soil analysis (physical and chemical) to find out if the soil is suitable for planting and if it lacks some nutrients.

After the analysis and getting the results, treat the soil with reclamation fertilization that adds the missing nutrients. The most commonly used are manure and mineral fertilizers.

Calculate the required amounts of fertilizer, add it to the soil surface and plow it to a depth of 40 cm (15.7 in). After that, in the following years of cultivation, you can add mature manure every 3 or 4 years.

Before planting, it is necessary to remove all the remains of previous crops and plow the soil to a depth of 40 cm (15.7 in). It is recommended to cultivate field crops for 3 to 4 years before cultivating olives, because they clean the soil of possible fungal diseases that could be fatal for young olive trees.

After doing the necessary pre-treatment of the soil, trench it to 100 cm (39.4 in) in depth. This way the soil will become light, aired and more suitable for planting. If the soil is not light enough, young olive seedlings could dry out because their roots cannot grow through the solid and dense soil. After trenching, the soil must be leveled and flattened.

For planting olives outdoors, it’s recommended to use olive seedlings that are previously grown in pots or containers. Its soil is not separated from the roots so don’t water the plant a few days before planting them outdoors. This way, the planting will be grow more successfully. It is not recommended to plant seedlings that have bare roots because it can be easily damaged, which will slow down the growth of the plant.

The seedling should be carefully removed from the pot, making sure that the root does not touch the fertilizer. Therefore, before planting, put a layer of soil between the roots and the fertilizer.

After planting, place the light soil around the seedling and water it.

Best time to plant

Olives can be planted all year round, but it is still recommended to plant it in the spring when the danger of frost has passed. If there is no danger of frost in the area where you are planting, you can plant it in early fall. Namely, in such areas planting in the fall is recommended because the plant will be fully grown by spring (canopy, root) and thus will be more resistant to drought.

Olive trees climate

Olives will grow best when exposed to gentle air flow and wind currents. Avoid foggy areas and areas where there is no constant air flow. If you plan to plant it in a windy region, always choose sheltered places. In that case, the tree will bear more fruit.

Soil

Olives are planted into the pits that are approximately 50 cm (19.7 in) long/wide and 35 cm (13.8 in) deep. The yield will be the biggest if olives are planted on flat and slightly sloping terrain. Plant it in drained and shredded soil, and avoid heavy and dense soil. Sandy soils are recommended for olive cultivation.

Water

Olives are very sensitive to lack of water, especially during the summer. Lack of water reduces the yield of olives, so it is recommended to irrigate olive groves. Irrigation of olive groves increases the yield by 50%. Although the tree needs water all year round, irrigation is especially recommended during flowering and fruit growth. Be careful if you plant olives on heavy soils, because in that case the humidity is higher around the roots which can harm the plant.

Olive cultivation

Before olive cultivation have in mind that it’s important to have a some sort of stake that will support each plant when it starts to form a canopy and protect it from strong winds.

The stake must be either wooden, steel, plastic, concrete, stainless steel or galvanized, up to 1.8 m (5.9 ft) long and up to 8 cm (3.1 in) wide. Place it 1 m (3.3 ft) above the ground and at least half a meter (19.7 in) in the ground. If the area is exposed to strong winds, make sure to place it deeper in the ground.

Also have in mind that the olive must grow along the stake for about five years, while in the regions with stronger winds it is recommended for longer use of the stake, i.e. until the root is completely developed.

Weed control

In order to reduce the weed and avoid frequent tillage, it is advised to sow grass in your olive grove. The soil is thus protected from erosion, enriched, and machines can move freely through the olive grove. However, sowing grass in young olive groves is not recommended because like young olive plants, grass needs a lot of water and as a result can take away the humidity your olive plants need. Therefore, perform grassing only when the plant strengthens, approximately after 6 years.

Fertilization

As important as ameliorative fertilization before planting olives is, it is just as important to do the fertilization during cultivation. It is necessary to enrich the soil with minerals and humus as well as maintain its fertility the entire time of cultivation.

In case you're planting olives in the temperate-warm climate, fertilize the soil before the first fall rains. Use the basic fertilizers such as mineral NPK fertilizer for deeper tillage. This ensures that plants will have enough phosphorus and potassium during the vegetation period.

In addition to this it is also recommended to add some nitrogen which will protect your plants from summer droughts and make sure it grows well during the fall. The nitrogen is most needed in the spring when it's washed out and eroded with the soil.

The mentioned spring fertilization should be done twice - at the end of February and at the end of April. The fertilization is applied by lightly plowing it into the soil so the nitrogen can penetrate the root area where it's most needed.

The standard basic and spring fertilization should be done every year and depends on the chemical analyzes of the soil. Olives can also be fertilized through irrigation (by adding dissolved nutrients in water) and foliar fertilization (spraying the leaves with fertilized water). Foliar fertilization is recommended during drought or during vegetation period.

Lately, organic fertilizer such as manure is no longer used in cultivation as the amount of nutrients in organic fertilizers are lower than in mineral fertilizers. In addition, it is no longer possible to buy such large quantities as in previous years. However, if you have it, apply it every 3 to 4 years.

Olive grove maintenance

The olive grove must be frequently maintained. While plants are still young, regularly check the stakes and plow soil every year. Tillage also involves the reduction of weeds and is done only on the surface, 10 to 20 cm deep (32.8 to 65.6 in), in order not to damage the root system.

The first tillage is done after the first olive harvest fall, while the next 2 to 3 treatments are done in spring and summer.

In fall, the soil should be plowed and fertilized while in the spring it should be slightly lightened to prevent weeds. Keep in mind that you don’t damage the root. Also, nitrogen can be applied to the soil in addition to the basic plowing.

During summer, it is necessary to perform only shallow tillage which preserves humidity in the soil and destroys the remaining weeds.

Olive tree pruning

Pruning is one of the most important maintenance treatments in the olive grove, and should be performed regularly from the beginning until the year of olive cultivation. However, there is a big difference in pruning olive trees in the first years of cultivation and later when the olive begins to bear fruit.

Pruning should be done with a lopper or a pruning saw. The cut should be round and placed perpendicular to the branches. When using a saw, the incision must be additionally done by the fruit knife and finally the cut coated with fruit wax.

The main goal of pruning is to grow olives with a firm trunk and regularly shaped branches. This makes it easy to perform all the other things that are needed in the olive grove.

There are 2 different types of olive pruning: pruning for productivity and pruning for cultivation.

Pruning for productivity

In the case, olives are already yielding and pruning forms the growing form of olives and “encourages” olives to achieve the best possible yield.

Pruning for cultivation

Pruning for cultivation should be done from the first stage of cultivation (raising the plantation) until the trees start to form the canopy and bear fruit. The main goal of this type of pruning is to bring the olives to fruition as soon as possible and to achieve faster growth and high yields.

During the first years of cultivation, the olive trees must not be pruned or should be pruned minimally, while later its canopy should be shaped so that the tree receives as much light as possible for growth. Young olives should not be pruned because pruning encourages the growth of young shoots that can prolong the onset of fruiting. In addition, there is a danger of disrupting the balance between canopy and root.

Young trees should be pruned by removing shoots and trying to achieve equality in all parts of the canopy. Removing shoots that go from one part of the canopy to another and side shoots on the trunk to reduce the competition between the side shoots and canopy or conductive branches.

It is recommended that the trees are pruned after February, when you can differentiate the buds that grow shoots form those that bear fruit. The best time to prune is in March or April. Earlier pruning will induce the development of wood buds.

It is not recommended to prune the tree during bad weather or dew as water that enters the branches can trigger the disease transmission in olive tissue.

With proper pruning, the olive tree will give yield in the third or fourth year after planting the seedlings.

Growing olive trees in containers

The olive tree can also be grown in a container, but keep in mind that it is not the usual olive tree but a dwarf olive that is grown as a houseplant.

The lifespan of such olive houseplants variates is approximately 10 years so take into consideration that garden centers are selling two- to three-year-old plants, so you’ll enjoy your tree for only 7-8 years.

The size of a dwarf olive will depend on the container in which it will be planted. The formation of the canopy will also depend on the container - the bigger the size of the container, the bigger the size of the roots and the crown of the olive tree will be.

Place the container in a place where it will get enough light, but again as far away from artificial heat sources (radiators) as possible. The best time to transplant olives is during the spring. Plant the tree in quality soil, preferably in a purchased premade substrate consisting of humus, peat and sand. If you can’t find the premade soil for olive trees, choose the one for the cacti as it will suit your plant best. Place pebbles at the bottom of the container to perform permanent drainage.

You can place it outdoors (in the garden or balcony) during spring and summer because it will grow better. Bring it indoors before winter, but be careful as olives do not like large temperature changes, so you’ll need to gradually get your plant used to room temperature.

Since it does not tolerate excess water around the root system, it is important that you secure the excess drains into a saucer under the container. Moisture around the roots could lead to rot. Water it as needed, best when the substrate is completely dry.

In the summer months, your plant will need a little more water, but don’t exaggerate. Watering it once a week will suffice. Never water the leaves.

After your tree starts flowering in the summer, prune it by removing its main shoots and all the dry and old branches. During the winter, allow it to rest at slightly lower temperatures from -2 to 15°C (28.4 to 59°F). Also, reduce watering during winter months - twice a month is enough.

Harvesting olives

Harvesting olives depends on whether you harvest olives for oil production or for consummation. The harvest of table varieties can be done when the green skin of the olive is slightly yellowed and softened. The harvest of black table varieties can be done when the olive fruit is fully ripe.

Table varieties must be hand-picked so that fruits intended for eating and canning remain undamaged. Table varieties for olive oil production can be harvested when one third of the fruit is green (yellow), one third is purple and one third is black. Harvest time depends on the region, variety of the plant and weather conditions, but is recommended from the second half of October to the second half of December. It can be done both by hand and machines, depending on the yield amount.

Preserving olives

Olives must be used quickly after harvest, and you can store them for up to a week. Keep them in a dry and airy place, in layers up to 10 cm (3.93 inches).

Olive diseases

The olive can be attacked by diseases and pests during cultivation, and in order to protect the plant in time, it is important to identify them and apply the correct treatments.

Common olive diseases are peacock spot and olive knot.

Peacock Spot

Peacock spot is a fungal disease that attacks leaves, stems and fruits. You will recognize the disease by the dark green oily spots on the upper side of the leaves. Over time, the middle part will turn yellow, while the edges will remain green. The spots changes color all the way to brown and black, and the leaves will completely turn yellow, dry out and fall off.

In some cases, the olive tree can lose all its leaves, which affects its yield. To prevent disease, ensure regular airflow and do not raise the olive grove in areas with high humidity. Perform regular pruning and plant less sensitive olive varieties.

Apply insecticides in early September, before the first rains until the end of fall. You can harvest the fruits at least 56 days after using insecticides.

Olive knot

It is a bacterial disease that attacks newly developed olive branches. Symptoms appear on the root, trunk and leaves, and the first sign that an infection has occurred are green lumps that eventually become wooden and crack. Inside the lump you’ll see a semi-liquid mass with bacteria that is spreading to the entire olive grove.

Olive knots on young trees can be stopped only by removing entire trees to prevent disease to spread to the entire olive grove. Older trees won’t suffer significant damage. With proper care, the trees will continue to grow and bear fruit.

It is recommended to regularly disinfect tools after pruning and to prune infected trees last.

Olive pests

The olive tree can be attacked by different types of parasites. Some will harm seedlings by eating young shoots and leaves, while others attack mature olives and their fruits.

Jasmine Moth

This white-colored pest usually attacks the plant at night. It’s most frequent in April and May and it feeds on olive leaves and buds. If you notice symptoms apply the protection treatment with insecticides. According to the instructions, it can be applied more than once.

Palm Weevil

Except olive trees, palm weevils also attack grapevine, peach, carob and almond trees. They can do a lot of damage to olive trees by eating its leaves. If there are more of them they need be controlled with chemical agents. However, they've evolved resilience to most of them so it's better to protect the trees with blocks (resin, glue), so they can't reach leaves.

Leopard Moth

Leopard Moth is actually a white butterfly with black dots on its wings. The caterpillars are initially light yellow while later become darker. This pest damages olive trunks by drilling tunnels which results in branches and even the whole tree drying. Remove the damaged branches, and add a volatile insecticide to the tunnels which you finally cover with fruit wax.

Olive Moth

It is the most frequent pest that can be seen on olive trees at any time of the year. The damage is caused by caterpillars that attack flowers, fruit and leaves, depending on the stage of plant development and the severity of the attack. It should be controlled by different chemical agents depending on generation of moth you need to control.

Olive Fruit Fly

The olive fruit fly is the most dangerous pest to olives. It has green eyes, a yellow-brown body and transparent wings with black dots on the edges. It can be noticed when the air humidity is high with slightly lower temperatures. It’s the larva that causes damage to olives causing wounds through which microorganisms enter the tissue.

In order to control it, it is best to regularly monitor their appearance and catch them with flytraps before they lay eggs in the fruit. In addition, you can also spray the canopy with insecticides.

Scale Insects (Coccoidea)

They appear in dense olive canopies where there is not enough light and the moisture level is higher. Scale insects cause damage by sucking fruit juices and at the same time secreting dew which later causes the fungi development. The treatment is the same as for the fruit fly and the olive moth.

Olive uses

Olive fruits are mostly cultivated for olive oil production. Olive oil can be made by cold-pressing, by separating the oil with hot water or steam. The highest quality olive oil made by cold-pressing is known as extra virgin olive oil.

The water temperature for the cold-press process should not exceed 25°C (77°F). Oil should be stored in dark glass bottles and kept in dark places at a constant air temperature of 15°C (59°F).

Olive oil is especially popular in Mediterranean countries where it is used to season dishes, cooking and frying.

Olive oil also has many health benefits as it is full of valuable vitamins, minerals and antioxidants.

Table varieties are used for consumption - addition to pizza, cold salads, pasta, and risottos or added to bread, pastries or focaccia.

In addition to fruits, olive leaves are also used for preparation of olive tea. In order to make tea, the leaves can be picked all year round. Tea is used to lower sugar and high blood pressure, and is prepared by pouring 15 g of leaves with half a liter of boiled water. After 15 minutes, the tea is ready to consume and can be drunk three times a day.

History

It is believed that the olive has been used for up to 7,000 years. It may originate from Crete and later spread to Greece, Egypt, Palestine and Asia.

The olive has been described throughout history as a symbol of strength, loyalty and fidelity. It has a special place in Greek mythology, and was also described by the ancient Egyptians.

In the past, olive oil was so appreciated and sold at high prices. In addition to that, it is a well-known fact that it was stored in amphorae as a prize for the winners of the Olympic Games.

The olive is also valued in Christianity. It is mentioned in the Bible through an event related to Noah’s ark when a dove was carrying an olive branch in its beak, and it was also used to greet Jesus when he came to Jerusalem.

Photo: Carabo Spain / Pixabay