Onion “starts” offer home gardeners a significant advantage over planting seeds, providing a pathway to a faster and more reliable harvest. These starts are typically young, actively growing onion seedlings or small, dormant bulbs called sets, already past the fragile germination stage. Utilizing starts allows for earlier planting and a more mature plant going into the main growing season. This method bypasses the lengthy and unpredictable process of growing onions from tiny seeds, making the cultivation of large, quality bulbs more accessible.
Selecting the Right Variety and Preparing the Site
Successful onion cultivation begins with selecting a variety suited to your specific geographic latitude. Onions are highly sensitive to photoperiodism, meaning the length of daylight hours triggers the plant’s shift from producing leaves to forming a bulb. Varieties are categorized as short-day, intermediate-day, or long-day types, each requiring a different minimum number of daylight hours to initiate bulbing. Planting the wrong type will result in a failure to form a marketable bulb, yielding only green tops.
Short-day onions require about 10 to 12 hours of daylight and are suited for southern latitudes, while long-day varieties need 14 to 16 hours of daylight and are ideal for northern regions. Intermediate-day onions require 12 to 14 hours of daylight and thrive in the middle latitudes. Most home gardeners plant their starts in early spring, as soon as the soil is workable, allowing the plant to establish large green growth before the bulbing phase begins.
The planting site should receive a minimum of six to eight hours of direct sunlight daily, as onions require full sun for optimal growth. Onions are shallow-rooted and perform best in loose, well-drained soil with a high organic matter content. A soil pH between 6.0 and 7.0 is preferred, and testing the soil beforehand can help determine if amendments are needed to adjust the acidity. Incorporating a few inches of aged compost or well-rotted manure into the top six inches of soil will improve both drainage and fertility.
Step-by-Step Guide to Planting Onion Starts
Before planting, handle the onion starts gently to minimize stress to the roots and delicate stems. If the roots are excessively long or tangled, a light trim to about an inch in length can encourage new root development after transplanting. The green tops can also be trimmed back slightly, removing about one-third of the foliage. This reduces the surface area for water loss and helps the plant focus its energy on root establishment in the new location.
Using a trowel or a hoe, create a shallow furrow or individual planting holes in the prepared soil. Planting depth is important, as planting too deep can inhibit the plant’s ability to form a proper bulb. The starts should be set so that the white bulb base is covered by about one inch of soil. This ensures the roots are well-covered but the neck remains near the surface.
Proper spacing is necessary to allow the bulbs to expand to their full size and ensure adequate air circulation. For large, mature bulbs, space the starts approximately four to six inches apart within the row. If the goal is to harvest some as green onions early in the season, a closer spacing of two inches can be used, planning to remove every other plant for early consumption. After placing the start in the ground, gently firm the soil around the base of the plant to eliminate any air pockets and ensure good contact between the roots and the surrounding soil.
Ensuring Establishment: Initial Watering and Nutrient Management
The first step immediately after planting is a thorough and deep watering to settle the soil around the roots and alleviate transplant shock. Onions have a shallow root system, meaning they are highly dependent on the moisture content of the topsoil. Consistent moisture is necessary during the initial establishment period. This requires roughly one inch of water per week either from rainfall or irrigation.
Because the goal during this initial phase is to maximize green, leafy growth before bulbing begins, the plants have a high requirement for nitrogen. A light application of a nitrogen-rich fertilizer can be applied after the root systems have developed, usually a few weeks after planting. This initial feeding supports the development of the foliage, which is directly correlated to the final size of the bulb.
Weed control is important during the establishment phase, as weeds aggressively compete with the shallow-rooted onions for water and nutrients. Applying a light mulch of weed-free organic material, like grass clippings or straw, can help suppress weeds and conserve soil moisture. Removing any emerging weeds by hand or with shallow cultivation immediately after planting reduces competition. This ensures the young onion starts receive the full benefit of available resources.