How to Cultivate Olive Trees
Olive trees are widely cultivated worldwide, except for Antarctica. The Mediterranean Basin alone is home to approximately 2,000 varieties differing in fruit size, shape, and color. Below are the steps for cultivating olive trees:
Choosing the Land
When selecting land for planting olive trees, ensure it is in a location not exposed to extreme cold. Temperatures below -5°C can kill young trees, while temperatures below -9°C pose risks to mature trees. However, olive trees require around 200 hours of slightly below 7°C during winter to produce fruit. Resistance to cold depends on the tree variety, temperature fluctuations, water conditions, and frost occurrences. During the flowering period in April and May, trees should be protected from extreme cold, heat, and strong winds to ensure good fruit and oil quality.
Olive trees thrive in all soil types except poorly drained soils, as waterlogged conditions are a leading cause of tree death. For clay soils, planting on slopes is recommended. Medium soil fertility suffices, but it’s advisable to test the soil for nutrient deficiencies, toxic materials, or fungal spores, especially if the land previously grew crops susceptible to fungi like tomatoes, cotton, or peppers.
Preparing Seedlings
Germinating Rootstocks
Olive seeds or pits can be used to produce rootstocks for grafting. Mature fruits are collected in November and December to extract seeds within six hours of harvesting. The seeds are cleaned using sand and water or a sodium hydroxide solution. For every 100 kg of seeds, a solution of 250 grams of sodium hydroxide mixed with 100 liters of water is needed. After cleaning, seeds are stored in a dry place covered with paper and away from rodents.
Before planting, seeds are soaked in water for 15-20 days, with the water changed twice daily. Germination can be enhanced by splitting or cutting the seeds before soaking or by adding 5 ml of naphthalene acetic acid to 10 liters of water for every 100 kg of seeds.
Seeds are placed in a suitable-sized bed, with 4 kg of seeds (about 1,500 seeds) per square meter, covered with a 1-2 cm layer of a sifted mixture of equal parts soil, sand, and organic compost. The mixture is watered and left uncovered on sunny days or covered with plastic on cold or rainy days. Watering is done every three days. Under optimal conditions (13°C temperature, humidity, and light), seeds germinate in approximately three months.
Seedlings remain in the mixture until 6-8 leaves appear. In April, on a cloudy day, seedlings are transplanted. The main root is trimmed to prepare for potting, ensuring it is straight. Soil is pressed around each seedling, which is then placed in a shaded area, watered, and fertilized regularly until it’s ready for grafting after a year.
Grafting on Rootstocks
Grafting is typically done in winter when both the scion and rootstock are dormant. Field-planted trees are grafted in place, while potted plants can be brought indoors for the procedure. Scions are selected from the previous season’s seedlings, ensuring they are healthy and pest-free.
After cutting the scions with a sharp, clean knife, they are stored in moist cloth or burlap bags and labeled with the plant’s origin, variety, and collection date. Scions can be stored at 0-1°C in coolers, avoiding refrigerators used for storing fruits or vegetables due to ethylene gas that inhibits growth.
Common grafting techniques include:
- Cleft graft
- Bark graft
- Side-veneer graft
- Splice graft
- Whip-and-tongue graft
- Saddle graft
- Bridge graft
Using Cuttings
Cuttings are commonly used for vegetative propagation. After selecting appropriate cuttings, they are separated from the parent plant using a sharp blade, and flowers and buds are removed to promote root growth. The blade should be sterilized with alcohol or a bleach solution.
Cuttings are placed in a rooting medium, such as perlite, peat moss, or a mixture of both. The medium should be well-draining yet retain moisture and nutrients. Cuttings can also be rooted in water, although this may lead to shock during transplantation.
Preparing the Land
Before planting, the soil should be prepared by removing weeds and breaking it up through plowing to enhance oxygenation and water movement. In loose soil, ridges can be formed to stabilize the land. Roots typically grow 20-80 cm deep, depending on soil texture and fertility.
Spacing between trees is essential to ensure adequate sunlight. For large varieties, 9 meters between trees is recommended, while smaller varieties like Arbequina can be planted 7.5 meters apart. When used as a hedge, spacing of 1.5-3 meters between trees and 4-6.7 meters between rows is suitable.
Caring for Olive Trees
Key care practices include:
- Irrigation: Trees need about 2.5 cm of water weekly. Some farmers reduce watering during fruit maturation to improve oil quality.
- Fertilization: Olive trees primarily need nitrogen, applied in spring and summer. Mature trees may also require potassium or boron occasionally.
- Pruning: Done in early spring, pruning removes deadwood and promotes productivity. Avoid topping trees unless grown as decorative hedges.
- Cold Protection: Young trees (under five years) should be protected from frost by mounding soil around the base in late November and removing it by late March.
Seasonal Care
- Winter: Spray with copper to prevent diseases like Peacock Spot.
- Spring: Prune, fertilize, and start irrigation.
- Summer: Control weeds, irrigate via drip systems, and provide nitrogen fertilizers.
- Autumn: Continue irrigation until harvest, apply copper sprays, and clean fruits thoroughly before processing.
Common Diseases
- Armillaria Root Rot: Caused by Armillaria mellea, leading to gradual wilting and root decay.
By following these steps, olive trees can thrive, ensuring high-quality fruit and oil production.
