Onion

Planting methods vary by region, utilizing either direct seeding, planting sets (small immature bulbs), or transplanting greenhouse-grown seedlings. The choice depends on the length of the growing season and the target bulb size.

In temperate climates, planting sets is the most common approach for amateur and small-scale farmers as it guarantees a harvest even in shorter summer periods. Direct sowing requires specialized equipment to ensure accurate seed depth and spacing.

Seeds should be sown at a depth of 1-2 centimeters in well-prepared soil. Proper spacing (10-15 cm between plants) is essential to prevent overcrowding, which can lead to smaller bulb sizes and higher disease risk.

Timing the sowing correctly is vital; planting too early in cold soil can lead to premature bolting, while planting too late may not provide enough time for proper bulb maturation before the onset of autumn rains.

Onions are highly sensitive to day length and light intensity. Photoperiodic sensitivity determines when the bulb begins to form, making the choice of variety appropriate for the specific latitude crucial for success.

The crop thrives in well-drained, fertile, sandy loam soils with a pH between 6.0 and 7.0. Soils with high organic matter content are preferred to maintain consistent moisture levels during the active growth phase.

Adequate water is critical during the bulb development stage, but it should be restricted as the harvest approaches. Excess moisture during the late growth phase can lead to fungal infections and poor bulb storage quality.

Onions require a temperate climate. While they are frost-tolerant in early stages, the optimal temperature for bulb development is between 15 and 25 degrees Celsius, with dry weather being ideal for maturation.

Weed management is a top priority in onion farming. Due to their sparse foliage, onions cannot effectively compete with weeds, which can quickly overwhelm the crop and drastically reduce yields.

Global onion production is characterized by high yields, typically ranging from 40 to 80 tons per hectare in intensive farming systems using modern hybrid varieties and drip irrigation.

Yield is significantly impacted by plant density, fertility management, and the control of soil-borne pathogens. Precision agriculture allows growers to monitor crop health and optimize nutrient delivery for maximum output.

High-quality yields are defined by uniform bulb size, firmness, and the condition of the outer dry skin, which acts as a protective barrier against external pathogens during storage.

The transition from manual to mechanized harvesting has greatly increased efficiency, allowing for large-scale production that meets the requirements of international markets and supermarkets.

Proper nutrient management, especially balancing nitrogen, phosphorus, and potassium, is essential to ensure that bulbs reach their full potential mass without compromising their shelf life or resistance to disease.

Downy mildew (Peronospora destructor) is the most destructive disease for onion crops, thriving in humid, cool conditions and capable of causing total crop failure if left untreated.

The onion maggot is a significant insect pest that feeds on the roots and bulbs, causing wilting and death of young plants. Crop rotation is the primary defense strategy against this pest.

Thrips are another major concern, causing silvering of leaves and significant yield loss by weakening the plant and promoting the spread of secondary viral infections.

Neck rot (Botrytis spp.) is a primary post-harvest concern, often entering the bulb through the neck during curing and developing into a soft rot during storage.

• Downy mildew
• Onion maggot
• Thrips
• Neck rot
• Pink root

Harvesting should begin when 50% to 80% of the foliage has naturally fallen over. This indicates that the bulbs have stopped growing and are ready to enter the curing phase.

Post-harvest curing is essential for long-term storage. Onions are left on the field or moved to a ventilated shed to dry, allowing the outer skins to papery and the neck to seal completely.

After curing, the tops are trimmed, leaving about 3-5 centimeters of the neck to prevent pathogens from entering the bulb core during storage.

Bulbs must be stored in cool, dry conditions with high airflow. Consistent temperature control (near 0 degrees Celsius for long-term storage) helps maintain dormancy and prevents sprouting.

Careful handling during all harvest and post-harvest stages is required to avoid bruising, as any mechanical damage serves as an entry point for fungal and bacterial infections.