Onion Yield and Storage Program: Global Grower Guide

By Ihumate

Harvested onion bulbs ready for grading

Table of Contents

Crop Background and Variety Selection

  • Match short-, intermediate- or long-day varieties to local latitude and the bulbing season. A poor daylength match causes premature or failed bulbing.
  • Choose locally proven, low-bolting varieties with resistance to downy mildew, purple blotch and pink root; align skin color and dry matter with fresh, dehydration or storage markets.

Soil Preparation and Planting

  • Use full sun and fine, well-drained soil near pH 6.0-7.0. Test before planting and incorporate fully composted organic matter plus required phosphorus and potassium.
  • Sow about 0.6-1.3 cm deep, with rows roughly 30-45 cm apart, then thin to 7.5-10 cm. Avoid deep planting so bulbs can expand.

Nutrient Management

  • Base P, K and sulfur on tests. Split nitrogen during leaf growth, then reduce it as bulbs enlarge; late excess N produces thick necks, delayed maturity and poor storage.
  • Use humic acid root-zone conditioning in low-organic-matter or compacted soil. Amino acid nutrition and seaweed extract can support recovery after transplant, cold or heat stress but do not replace NPK.

Irrigation Recommendations

  • Because roots are shallow, maintain even moisture, often near 25 mm per week after rainfall and evapotranspiration adjustments. Prefer drip irrigation and limit prolonged leaf wetness.
  • Stop irrigation when bulbs reach target size and about half the tops fall, allowing skins and necks to dry before harvest.

Pest and Disease Management

  • Monitor thrips with blue or yellow traps and leaf-sheath checks. Control weeds and excess N, conserve beneficials, and use locally registered neem or entomopathogenic fungi at low pressure.
  • Rotate for 3-4 years, plant clean material, improve airflow and drainage, and remove residues. Manage downy mildew, purple blotch, soft rot and root diseases from scouting data.

Harvest and Post-Harvest Handling

  • Harvest when about 50% of tops have fallen and begun drying. Avoid wet harvest and neck damage; remove injured, thick-necked and diseased bulbs.
  • Cure for 2-4 weeks in warm, dry, well-ventilated conditions. Grade only after necks and skins are dry, then store cool, dry and ventilated without freezing or condensation.

Recommended Ihumate Products

Sources