Spring onions, frequently referred to as scallions or green onions, are young Allium cepa plants harvested before the underground bulb has fully developed. The goal is to maximize the green tops and the small, tender white base, not the mature bulb. Knowing the precise timing is paramount for a successful yield of these mild, versatile vegetables. The best time to plant depends entirely on the specific planting material used, whether seeds or small bulbs, and the local climate conditions.
Optimal Planting Timelines
Direct sowing seeds is the preferred method for most home gardeners and should commence as soon as the soil is workable in the spring. This typically means the ground is no longer frozen and has dried enough to be crumbled. This often translates to four to six weeks before the last expected frost date. Planting seeds early capitalizes on the cool, moist conditions necessary for optimal germination and robust root development before the summer heat arrives.
Germination is slow below 50°F (10°C) but becomes reliable when soil temperatures are consistently between 60°F and 75°F (15°C and 24°C). Sowing seeds too late, when temperatures are consistently above 75°F, can stress the young plants. This stress leads to poor establishment or premature bolting, where the plant focuses on producing a flower stalk instead of foliage.
Planting sets, which are small, immature bulbs, allows for an even earlier start than using seeds alone. Sets are more robust and less susceptible to early cold snaps, permitting planting up to two weeks earlier than seeds. Gardeners often place sets into the ground as soon as the soil thaws, sometimes six to eight weeks before the last frost, to gain a significant head start.
These small bulbs should be planted about an inch deep, with the pointed tip facing upward, and spaced closely, only one to two inches apart. This close spacing is possible because they will be harvested before requiring space for bulb expansion. Utilizing sets can provide a harvest that begins as early as six weeks after planting, significantly earlier than seed-sown crops.
Techniques for Continuous Harvest
To ensure a steady supply of fresh spring onions, gardeners utilize a method called succession planting. This involves sowing small batches of seeds every two to three weeks, beginning immediately after the initial spring planting. Continuing this staggered schedule until mid-summer prevents a large glut of the crop all at once and guarantees a sustained supply of tender greens.
Even as spring transitions into summer, the practice continues, though plants may mature slightly faster in warmer soil conditions. The final succession planting should occur approximately 60 days before the first expected hard frost in autumn. This timing allows enough time for the plants to reach a usable size before they enter dormancy.
A separate planting window exists in late summer or early autumn, typically August or September, for an overwintering crop. Planting specific, hardy varieties during this time allows young plants to establish a robust root system before the ground freezes. These plants remain semi-dormant through the winter months and resume vigorous growth rapidly as the soil warms in early spring. This cold-weather strategy provides the earliest possible harvest the following year, often several weeks ahead of spring-sown seeds.
Site Preparation and Environmental Needs
Regardless of the planting material or time of year, successful growth hinges on preparing the optimal planting medium. Spring onions require a loose, well-draining soil structure, preferably amended with aged organic matter like compost. This prevents waterlogging around the developing roots. Compacted or heavy clay soils impede fibrous root growth and can lead to fungal diseases or rot.
The ideal soil pH for spring onions is slightly acidic to neutral, generally between 6.0 and 7.0, which maximizes nutrient availability. While they tolerate cooler temperatures, the soil must be maintained above 40°F (4°C) for meaningful growth to occur. They perform best when situated in an area that receives full sun, meaning a minimum of six to eight hours of direct sunlight daily.
Adequate light exposure is necessary to develop the deep green color and concentrated flavor. When direct-sowing seeds, they should be covered with only a quarter to a half-inch of fine soil. Planting too deeply can exhaust the seedling before it reaches the surface. Maintaining consistent, shallow moisture during germination is paramount for successful sprouting. Once established, thinning the seedlings to about an inch apart ensures each developing plant has enough space to grow a usable white base.