Here is the translation of the article about olive tree cultivation into English:
How to Grow Olive Trees
Olive trees are widely cultivated worldwide—except in Antarctica—with nearly 2,000 different varieties in the Mediterranean region alone, differing in fruit size, shape, and color. Below is a detailed guide to growing olive trees:
Selecting the Land
When selecting a site to plant olive trees, ensure it is not exposed to severe cold. Temperatures below -5°C (23°F) can kill young trees, while temperatures below -9°C (15.8°F) can threaten mature trees. However, olive trees require approximately 200 hours of temperatures slightly below 7°C (44.6°F) during winter for fruit production.
Resistance to cold also depends on factors such as tree type, temperature fluctuations, water conditions, and frost occurrences. During the flowering period (April and May), trees must be protected from low and high temperatures and strong winds to ensure high-quality fruits and olive oil.
Olive trees can grow in all types of soil except poorly drained soils, as water saturation is the leading cause of tree death. It’s preferable to plant olives on slopes if the soil is clayey. As for soil fertility, medium fertility is sufficient, but testing the soil for nutrient deficiencies, toxins, or fungal spores is recommended, especially if crops prone to fungi like tomatoes, cotton, or peppers were previously grown in the field.
Preparing the Saplings
Olive trees can be propagated in several ways, with sapling cultivation being the most common. Below are the steps to prepare and plant olive saplings:
Rootstock Germination
To produce rootstocks, you can use olive seeds extracted from ripe fruits during November and December. Seeds should be cleaned within six hours of harvest using sand and water or a sodium hydroxide solution (250g of sodium hydroxide in 100 liters of water for every 100kg of seeds).
After cleaning, store seeds in a dry place covered with paper and protected from rodents. About 15–20 days before planting, soak the seeds in water, changing the water twice daily. Germination can be stimulated by notching or cutting the seeds before soaking or adding 5 ml of naphthaleneacetic acid to 10 liters of water per 100kg of seeds.
Place the seeds in a suitable-sized container, covering them with 1–2 cm of a sieved mixture of equal parts soil, sand, and natural fertilizer. Water the mixture and leave it uncovered during sunny days or covered with plastic during cold or rainy days. Water the seeds every three days. Seeds typically germinate within three months if conditions are optimal—temperatures around 13°C (55.4°F), proper humidity, and light.
Once saplings develop 6–8 leaves, usually by April, choose a cloudy day to transplant them. Cut the primary root’s tip, ensuring it remains straight before planting the saplings in pots or containers. Ensure the soil is compacted around the saplings, and keep them in shaded areas, watering and fertilizing them regularly until they are ready for grafting after a year.
Grafting onto Rootstocks
Most grafting is done during winter when both the scion and rootstock are dormant. Field-planted trees can be grafted in place, while potted plants can be grafted indoors and then placed in protected areas.
Scions are typically selected from last season’s saplings, ensuring they are free from pests, diseases, and damage. After cutting the scions with clean, sharp tools, store them in moist plastic or burlap bags, ensuring tools are disinfected with alcohol or a homemade bleach solution (1 part bleach to 9 parts water).
Scions can be stored at 0–1°C (32–33.8°F) in waterproof paper or plastic bags. Avoid using refrigerators recently used for fruits or vegetables, as they emit ethylene gas, which halts bud growth. Ensure scions are not frozen during storage.
There are several grafting methods for olive trees, including:
- 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 of herbaceous plants, ornamental woody trees, and some fruit trees. A cutting is a part of the plant (stem, leaf, or root) that can develop roots and grow into a new plant.
After selecting a suitable cutting, remove flowers and buds to encourage root formation. Sterilize cutting tools with alcohol or a bleach solution to prevent disease transmission. To enhance rooting, dip cuttings in rooting hormone containing a fungicide.
Place cuttings in a well-draining, porous medium such as commercially prepared rooting mixtures. High-quality mixtures are recommended as they are sterile and free of fungi, bacteria, and pests. If cuttings rot in high-humidity environments, use coarse perlite, or a mix of equal parts peat moss and perlite for good aeration and moisture retention.
Maintain optimal rooting conditions:
- Moisture: Ensure the medium is fully moistened.
- Temperature: Keep the medium and air between 21–24°C (69.8–75.2°F).
- Light: Provide indirect light.
After 2–3 weeks, gently test for root formation by tugging on the cutting. If there’s resistance, carefully transplant it for further growth.
Preparing the Soil and Planting
Before planting rooted olive cuttings, prepare the soil by removing plant residues and plowing it to improve aeration and water movement. Ensure adequate spacing between trees to allow sunlight to reach all parts, preventing shading and ensuring optimal fruit production.
- Standard spacing: 9 meters (29.5 ft) between trees.
- Small varieties (e.g., Arbequina): 7.5 meters (24.6 ft) between trees.
- Hedges: 1.5–3 meters (4.9–9.8 ft) between trees and 4–6.7 meters (13.1–22 ft) between rows.
Caring for Olive Trees
- Irrigation: Olive trees need 2.5 cm of water weekly. Reduce watering during fruit ripening to improve olive oil quality.
- Fertilization: Olive trees mainly need nitrogen, applied in spring and summer. Avoid over-fertilizing to prevent excessive vegetative growth.
- Pruning: Prune trees in early spring to remove dead or unproductive wood.
- Cold Protection: Protect young trees (under five years) from frost by piling soil 15–30 cm around the trunk during winter.
Common Diseases
- Armillaria Root Rot: Caused by Armillaria mellea. Symptoms include gradual thinning and wilting of branches, discoloration of roots, and the presence of white fungal mats.
- Peacock Spot: Caused by fungal infection, leading to defoliation and reduced fruit yield.
