Green onions (scallions or bunching onions) are popular in gardens due to their versatility and ease of growth. While most people are familiar with the plant’s long, hollow green stalks and mild white base, few have seen the seeds that start this process. Understanding the characteristics of these seeds is important for gardeners looking to save their own supply or ensure they are planting the correct Allium species. This guide details the physical appearance of the seed, how it is produced, and how to keep it viable for future planting.
The Physical Description of the Seed
Green onion seeds are instantly recognizable by their intensely dark coloration, appearing deep matte black or charcoal gray. This dark pigment is a protective coating covering the embryo, a common trait across the Allium genus. They are not perfectly round but possess a distinctive, irregular, and angular structure, often described as shield-shaped or wedge-like.
The surface of the seed is rough, featuring numerous irregular wrinkles that give it a pitted texture. These seeds are quite small; the average thousand-seed weight for green onions (Allium fistulosum) ranges only from 2.4 to 3.4 grams. While easy to manage in bulk, their minute size requires careful attention during planting.
Seed Origin: The Flowering and Bolting Cycle
Green onions are biennial or perennial plants, typically producing seeds in their second year of growth after overwintering. This process begins with “bolting,” where the plant shifts energy to reproductive growth by sending up a tall, rigid flower stalk from the center.
At the top of the stalk, a spherical flower head, known as an umbel, forms, initially enclosed in a papery sheath. Once the sheath splits, the umbel displays numerous small, white or greenish-white flowers that attract insect pollinators. After successful pollination, the flowers develop into small, three-part capsules, which hold the seeds.
The seeds mature inside these capsules, gradually turning from soft and white to hard and black over several weeks. Seed harvest is ideally timed when the seed head has completely dried out, turned brown, and a small percentage of the capsules have begun to split open. If the seed head is left on the plant too long, the capsules will fully open and drop the seeds naturally.
Distinguishing Green Onion Seeds from Other Alliums
Green onion seeds (Allium fistulosum) are distinct from common bulb onion seeds (Allium cepa), though they share a strong superficial resemblance. Both are black, shield-shaped, and have a wrinkled surface texture, which often causes confusion among gardeners. The most reliable physical difference between the two lies in their size.
A. fistulosum seeds are noticeably smaller than those of the common bulb onion, often measuring only about half the size of an A. cepa seed. This size disparity is the primary way to distinguish them physically. Furthermore, true green onion varieties will not form a large underground bulb, a functional distinction more significant than any minor visual difference in the seed itself.
When sourcing seeds, purchase packets explicitly labeled for bunching or scallion varieties to ensure the desired non-bulbing, cut-and-come-again growth habit. Relying solely on visual inspection to differentiate them from other Allium family members, such as chive or leek seeds, can be unreliable due to their physical similarity.
Handling and Storing Viable Seeds
Proper storage is necessary to maximize the planting success of green onion seeds, which have a relatively short shelf life compared to many other vegetable seeds. The germination rate of Allium seeds tends to decline significantly after the first one to two years. Therefore, it is best practice to use the seeds as soon as possible after they have been collected or purchased.
The ideal environment for long-term storage is cool, dry, and dark, which slows the seed’s metabolic processes. Storing them in an airtight container, such as a sealed glass jar or zip-top bag, protects them from humidity fluctuations. Since excessive heat and moisture cause viability loss, storing seeds in a refrigerator or cool basement is preferable to a shed or garage.
Gardeners who save their own seeds must ensure the harvested seed heads are completely dry before storage to prevent mold or rot. Adding a desiccating agent, like a small packet of silica gel, can absorb any residual moisture. Controlling these environmental factors ensures a higher germination rate when the seeds are sown.