Spring onions, often referred to as scallions or green onions, are a popular and versatile addition to many home gardens. These slender, mild members of the Allium family are distinguished by their long, hollow green tops and small, white, non-bulbing bases. They are highly favored by home growers because they require minimal space and offer a quick turnaround from planting to harvest. Understanding the time frames involved in their cultivation allows gardeners to plan for a steady, continuous supply.
Understanding the Growth Period
The time it takes to grow spring onions varies significantly based on the starting material used: seeds or sets. Starting spring onions from seeds is the longest method, typically requiring 8 to 12 weeks until they reach a usable size for harvest. Germination alone can take between 10 to 14 days, and this process can be slower if soil temperatures are very hot or cold.
A much faster option is to plant immature bulbs, commonly known as sets, which are small, dormant onions grown from seed the previous season. When planted, these sets already have a head start, often allowing for a harvest in 3 to 4 weeks. Sets are considered the easiest way to grow spring onions quickly because they bypass the slow initial germination and seedling stage.
Several environmental factors influence these timelines, primarily temperature and moisture. Spring onions thrive in cooler weather, but prolonged exposure to temperatures below 45°F can trigger bolting, or flowering, which affects the quality of the green tops. Consistent moisture is also important, as the plants have shallow root systems and will stress if the soil is allowed to dry out completely.
Essential Planting and Care Steps
Spring onions grow best in well-drained soil that is rich in organic matter. They benefit from an open, sunny location, though they will tolerate partial shade. Heavy, waterlogged soil should be avoided, as it can cause the young bulbs to rot.
When planting seeds, sow them shallowly, about 5 to 6 millimeters deep, directly into the prepared garden bed. If using sets, plant them just beneath the surface, about an inch deep, ensuring the root base is covered but the tops are not deeply buried. Planting sets too deeply can restrict the formation of the white shank.
Consistent maintenance focuses primarily on watering and managing space. Spring onions need regular watering to keep the soil consistently moist but never soggy, especially during periods of high heat. When growing from seed, thinning is necessary; seedlings should be separated to allow for 7 to 10 centimeters of space between plants. A minimal application of a balanced or nitrogen-rich fertilizer can support healthy green top growth.
Harvesting for a Continuous Supply
Spring onions are ready for harvest when their green tops reach the desired thickness, often compared to that of a pencil, typically around the eight-week mark when grown from seed. The most sustainable harvesting method is the “cut and come again” technique, which allows the plant to regenerate new growth. This involves cutting the green stalks about an inch above the soil line, ensuring the white base and root system remain intact.
The plant will respond by producing new green shoots from the center of the remaining base, allowing for multiple harvests from the same plant. Alternatively, the entire plant can be pulled from the ground. This is necessary if the goal is to use the entire white shank, but it ends the plant’s production.
A popular method for perpetual supply involves regrowing the white root ends of store-bought spring onions. Leave about an inch of the white stem with the roots attached and place this base in a shallow glass of water; new green growth will emerge within a few days. Once new roots develop, transplanting the base into soil will sustain the plant, offering a nearly endless supply of fresh green tops.