Onion Farming Guide: Growing Onions for Beginners and Small Farms

Introduction

Onions are a versatile, cool-season bulb crop grown in many climates. This guide covers the basics of growing onions, from choosing varieties to harvesting and storage, and is written for hobbyists and small-scale farmers.

What onions are and varieties

Onions come from the species Allium cepa and are produced in several forms, including storage onions, sweet onions, red onions, and white onions. They are grouped by day length in many regions: long-day, short-day, and day-neutral varieties. Selecting the right type for your latitude helps bulbs form at the right time.

Day-length categories

Long-day onions typically bulb well in regions with long daylight hours, short-day onions are common in southern areas, and day-neutral types offer flexibility across many locations.

Choosing varieties

Consider flavor, storage life, and disease resistance. For beginners, start with one or two reliable storage varieties and a sweet option for fresh markets.

Growing conditions

Onions prefer cool to mild temperatures for germination and steady growth, with long periods of daylight helping bulb development. They thrive in loose, fertile, well-drained soil and require consistent moisture without waterlogging.

Climate and season timing

Plant timing depends on your region: cool springs for fall harvest in mild climates or early spring in colder areas. In milder winters, some growers start in late winter for spring bulbs.

Field planning

Plan for crop rotation to reduce disease pressure and keep soil fertility balanced. Avoid planting onions where other alliums or heavy-feeding crops have grown recently.

Soil and bed prep

Ideal onion soil is loose, fertile, and slightly acidic to neutral (pH roughly 6.0–6.8). Work in organic matter like compost and ensure beds have good drainage. Raised beds can help in wetter areas.

Fertility basics

Apply a balanced fertilizer at planting and top dress with nitrogen during growth to support bulb development. Avoid excessive nitrogen late in the season to prevent lush foliage and poor bulb formation.

Planting and spacing

Onions can be grown from seeds, sets, or transplants. Spacing typically ranges from 4–6 inches (10–15 cm) between plants and 12–18 inches (30–45 cm) between rows, depending on variety and equipment.

Seed vs sets vs transplants

Seed-grown onions take longer to reach market size but offer more variety; sets and transplants can speed up establishment in cooler soils.

Water and fertility

Onions need steady moisture, especially during bulb formation. Water deeply less often rather than shallow daily irrigation. Use mulch to conserve moisture and reduce weeds.

Fertilizer strategy

Split applications of nitrogen through the season, complemented by phosphorus and potassium as needed. Monitor leaf color and growth to adjust feeding.

Pests and diseases

Onions face pests such as onion thrips and onion maggots, and diseases like downy mildew and botrytis. Good sanitation, crop rotation, and vigilance help reduce pressure.

Integrated pest management basics

Scout fields regularly, use row covers when practical, rotate crops, and select resistant varieties when available.

Harvest and storage

Harvest when leaves begin to fall and bulbs have firm necks. Cure bulbs in good airflow before storage in a cool, dry, well-ventilated space.

Storage tips

Store onions in a ventilated area away from potatoes and fruit to prevent sprouting and spoilage.

Market and profitability

Evaluate local demand, price volatility, and input costs. Small-scale growers often succeed with direct-to-consumer sales, farmers markets, and local co-ops.

Planning for profitability

Track yields, costs, and time requirements to optimize crop planning over multiple seasons.

Sustainability and farm planning

Rotate onions with non-allium crops to reduce soil-borne issues and maintain soil health. Use compost, conserve water, and select disease-resistant varieties when possible.