Complete Farming Guide
Onions Farming Guide
Allium cepa
105 million tonnes produced globally — grown in virtually every country on Earth
Onions are the most widely cultivated vegetable crop in the world, essential to cuisines across every continent. They are grown from Egypt to India, from Nigeria to Brazil. Onion prices are highly volatile — they can double or triple within weeks due to supply shortages, making them a high-risk, high-reward crop. India alone produces 26 million tonnes, and onion price spikes regularly make national headlines. The crop is photoperiod-sensitive: short-day varieties for the tropics, long-day varieties for temperate regions.
Quick Facts
Growing Season
Rabi (Winter) in tropics; Spring or Fall in temperate zones
Growth Period
100-150 days
Optimal Temp
15-25 degrees C (59-77 degrees F)
Water Needs
350-550mm
Top Producer
India
Yield / Acre
6-15 tonnes
Onions Growth Stages — What to Do at Every Stage
Nursery (if transplanted)
Days 0-45 (nursery)What to do
Sow seeds at 1cm depth in raised nursery beds. Use 2-3 kg seed/acre. Transplant seedlings when 15-18cm tall (pencil thickness) at 45-50 days. Space transplants 10-15cm apart in rows 20-30cm apart. Alternatively, direct-seed or use onion sets.
Watch for
Damping off (Pythium, Rhizoctonia) in nursery from overwatering. Purple blotch on nursery seedlings. Thrips damage (silvery streaks on leaves).
Establishment & Vegetative
Days 1-40 after transplantingWhat to do
Water immediately after transplanting. Apply 50% of nitrogen at transplanting. First weeding at 15-20 days. Onions are very poor weed competitors — keep fields clean. Apply pre-emergence herbicide (oxyfluorfen) or hand-weed 2-3 times.
Watch for
Transplant mortality from dry conditions or root damage. Thrips (Thrips tabaci) — the most damaging onion pest worldwide. Purple blotch lesions on leaves.
Bulb Initiation
Days 41-70 after transplantingWhat to do
Apply remaining 50% of nitrogen. Bulb formation is triggered by day length — ensure you are growing the correct variety for your latitude. Maintain consistent moisture. This is the period of maximum nutrient and water demand.
Watch for
Bolting (premature flower stalk) from cold exposure or wrong variety choice. Stemphylium leaf blight causing leaf tip dieback. Double or split bulbs from uneven moisture.
Bulb Development
Days 71-110 after transplantingWhat to do
Continue irrigation but begin reducing frequency as bulbs enlarge. Stop nitrogen application — late N delays maturity and reduces storage quality. Watch for signs of maturity: neck softening, leaf collapse.
Watch for
Basal rot (Fusarium) causing brown decay at the base of the bulb. Purple blotch advancing on leaves. Bacterial soft rot in wet conditions.
Maturity & Harvest
Days 111-150 after transplantingWhat to do
Stop irrigation when 50-70% of tops have fallen over. Harvest by pulling or undercutting. Cure in the field for 3-5 days (cover bulbs with their own leaves to prevent sunscald). Clip tops to 2cm and roots to 1cm. Store in well-ventilated, dry conditions.
Watch for
Rain during curing causes neck rot and bacterial soft rot. Sunscald (green shoulders) from direct sun on exposed bulbs. Harvest too early = poor skin development and short storage life.
Common Onions Diseases — Identification Guide
Purple Blotch
Alternaria porri
What you will see
Large, elliptical purple-brown lesions with concentric rings on leaves and flower stalks. Lesions often have a water-soaked border that extends above and below. Severe infections cause entire leaves to collapse. Can also affect bulbs in storage.
Conditions that favor it
Warm (20-30 degrees C), humid conditions with prolonged leaf wetness. Thrips damage provides entry points for the fungus. Worst when humid nights follow warm days. Spreads rapidly by wind and rain.
Stemphylium Leaf Blight
Stemphylium vesicarium
What you will see
Small, light yellow to brown, water-soaked lesions that merge into large leaf tip dieback. Affected leaf tips dry out and become papery. Often occurs together with purple blotch. Causes premature leaf death and reduced bulb size.
Conditions that favor it
Warm, humid conditions similar to purple blotch. More severe in tropical and subtropical regions (India, Brazil). Heavy morning dew and warm nights favor disease development.
Downy Mildew
Peronospora destructor
What you will see
Pale green to yellow, elongated patches on leaves that become covered with violet-gray fuzzy fungal growth (sporangia) under humid conditions. Infected leaves bend and collapse. Bulbs from infected plants are small and poorly developed.
Conditions that favor it
Cool nights (8-15 degrees C), high humidity (>95%), and morning dew. Fog and mist are ideal for spore germination. Night temperatures above 20 degrees C suppress the disease.
Basal Rot
Fusarium oxysporum f. sp. cepae
What you will see
Yellowing and dieback of outer leaves progressing inward. Roots rot and become watery brown. Cutting the bulb reveals brown discoloration advancing upward from the base plate. In storage, affected bulbs develop a dry, brown rot.
Conditions that favor it
Warm soil temperatures (above 25 degrees C) and mechanical damage to the base plate during transplanting or cultivation. Soil-borne pathogen persisting for many years. Worse in fields with continuous onion/garlic cropping.
Common Onions Pests — Identification & Damage
Onion Thrips (Thrips tabaci)
Damage
The most economically important onion pest worldwide. Adults and larvae feed by rasping leaf cells and sucking the exuded sap, causing silvery-white streaks and patches. Severe infestations cause leaves to curl, brown, and die back, reducing bulb size by 30-50%.
How to identify
Tiny (1-1.5mm), slender, pale yellow to brown insects. Hidden in the tight folds of inner leaves near the neck — peel back outer leaves to find them. Silvery feeding damage on leaves is the most visible sign. Threshold: 3 thrips per leaf or 30 per plant.
Onion Maggot (Delia antiqua)
Damage
Maggots feed on developing bulbs and roots, causing wilting and eventual plant death. Damaged bulbs develop bacterial soft rot. Most damaging to direct-seeded crops and during cool, wet springs.
How to identify
White, legless maggots (8mm) found feeding on the base plate and roots. Adults are small gray flies resembling houseflies. Pull up wilting plants — maggots are in the rotting tissue at the base. Rotate crops and avoid planting onions after onions.
Armyworm (Spodoptera exigua)
Damage
Larvae feed on onion leaves, creating ragged holes and windowpane-like transparent areas. Heavy feeding reduces photosynthetic area and delays bulb maturity.
How to identify
Green to brown caterpillars (up to 3cm) with a light stripe along each side. Egg masses on leaves. Feed mainly at night — scout at dusk. Frass pellets on leaves.
Onions Nutrient Management — NPK Guide
Nitrogen
60-100 lb N/acre, split 2-3 applications
Phosphorus
40-60 lb P2O5/acre at planting
Potassium
40-60 lb K2O/acre at planting
Application Timing
Apply 50% N + all P + all K at transplanting. Apply 25% N at 30 days and remaining 25% N at 45-50 days. Stop all nitrogen by bulb initiation — late N delays maturity and reduces storage life. Sulfur (15-20 lb S/acre) improves pungency and storage quality.
Onions Irrigation Schedule
Total Water Requirement
14-22 inches (350-550mm) total crop water use
Critical Stages
Establishment (first 2 weeks after transplanting), bulb initiation (40-70 days), and bulb development (70-110 days). Moisture stress during bulb development causes small, split, or double bulbs.
Irrigation Frequency
Every 5-7 days during peak demand. Reduce frequency as bulbs mature. Stop irrigation 10-15 days before harvest. Overhead sprinkler irrigation increases disease risk — drip or furrow irrigation is preferred.
Onions Economics — Cost, Yield & Profit
Cost per Acre
$1,500-3,000/acre
Yield per Acre
6-15 tonnes/acre
Revenue per Acre
$2,000-10,000/acre (highly volatile)
Profit per Acre
$500-7,000/acre
Regional Context
Onion is one of the most price-volatile crops. In India, prices can swing from Rs 5/kg to Rs 80/kg within weeks depending on supply. Farmers who time their harvest and storage well can earn 3-5x more than those who sell at harvest. Cold storage (or traditional curing and ventilated storage) is key to capturing off-season prices. Export-quality red onions from India, Nigeria, and Pakistan command premium prices. Input costs are moderate, but labor for transplanting and harvesting is significant.
Frequently Asked Questions — Onions Farming
Why are my onions bolting (going to seed)?
Onion bolting is triggered by cold exposure (vernalization) followed by long days. If seedlings are exposed to temperatures below 10 degrees C for 10+ days (in the nursery or after transplanting), they "think" winter has passed and initiate a flower stalk. Prevention: transplant seedlings at the correct size (pencil thickness, not too large), avoid very early transplanting that exposes seedlings to cold, choose bolt-resistant varieties for your region, and remove flower stalks immediately if they appear (the bulb is still usable but will not store well).
How do I store onions for longer shelf life?
Good storage starts in the field: stop irrigation 10-15 days before harvest, harvest when 50-70% of tops fall over, and cure (dry) in the field for 3-5 days. Clip tops to 2cm and roots to 1cm. For storage, maintain temperature at 0-2 degrees C with 65-70% humidity for long-term storage (up to 8 months) or 25-30 degrees C with good ventilation for ambient storage (3-4 months). Key factors: use appropriate storage varieties (kharif onions store poorly), avoid storing bulbs with thick necks or green necks, grade out damaged bulbs, and ensure good air circulation. Sprouting inhibitors (maleic hydrazide, applied 2-3 weeks before harvest) extend storage life.
How do I control thrips on onions?
Thrips are the number one onion pest. Integrated management: (1) Cultural: use overhead irrigation during establishment (physically washes off thrips), reflective mulch (confuses thrips), and avoid planting near wheat or garlic fields. (2) Biological: encourage natural enemies (minute pirate bugs, lacewings) by minimizing broad-spectrum insecticides. (3) Chemical: rotate insecticide classes to prevent resistance — spinosad, spinetoram (Group 5), cyantraniliprole (Group 28), or lambda-cyhalothrin (Group 3A). Add a surfactant to sprays since onion leaves are waxy and repel water. Spray in the evening when thrips are most active. Threshold: 3 thrips per leaf.
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