Growing onions provides a staple ingredient and a satisfying harvest for the home gardener. While some choose to sow tiny seeds directly, a popular and simpler alternative is to use onion sets. This method offers a distinct pathway to mature bulbs, favored by those looking for a head start in the growing season. Understanding the nature of the onion set is the first step toward a successful crop.
Defining Onion Sets and Their Creation
An onion set is a small, immature onion bulb grown from seed during the previous season but prevented from reaching full maturity. These sets appear as tiny, dried bulbs, typically measuring between one-half and three-quarters of an inch in diameter. The production process is designed to create this dormant state using an agricultural technique that stresses the young plants.
Commercial growers start by planting onion seeds at an extremely high density, forcing the seedlings to compete intensely for water and nutrients. This competition stunts growth, leading them to form tiny bulbs before the end of the normal growing cycle. The small bulbs are harvested early, usually when the tops begin to dry out, and are cured in a warm, dry place for several weeks. Curing removes moisture and forces the bulbs into dormancy, allowing them to resume growth and develop into full-sized onions when planted the following spring.
Practical Advantages and Disadvantages
Choosing onion sets over seeds involves weighing several practical trade-offs. One major advantage is the significantly accelerated timeline; sets are already a season old and can mature into harvestable bulbs much faster, often within 14 weeks of planting. They are also easier for beginners to handle than delicate seedlings, establishing themselves quickly with a high rate of success and offering resistance to early diseases and pests.
The primary drawback of using sets is the increased risk of the plant “bolting,” which means prematurely sending up a flower stalk and going to seed. Since the set is technically a second-year plant, previous stress can trick it into completing its life cycle instead of focusing energy on bulb development, resulting in a tough, unusable bulb. Another limitation is the restricted selection, as sets are usually available in only a few common varieties, unlike seeds which offer a vast array of specialized options.
Planting and Care Fundamentals
Planting onion sets should occur in early spring, as soon as the soil is workable, often two to four weeks before the last expected frost. Sets are tolerant of light frost and benefit from an early start, ideally when soil temperatures reach 45 to 50 degrees Fahrenheit. The planting location should receive full sun and consist of loose, well-draining soil enriched with organic matter.
The sets must be planted shallowly, with the pointed tip oriented upward and only just visible above the soil surface. Burying them too deep can negatively affect the final size and shape of the bulb. Space the sets approximately four to six inches apart, with rows spaced 12 to 18 inches apart, to give each bulb sufficient room to expand. Basic ongoing care involves consistent watering (about one inch per week, especially during dry spells) and regular weeding, as onions do not compete well for resources.