Why growing onions from seed beats sets for a healthier, more bountiful harvest

Gardening · Published 3 October 2026 Swipe more like this →

In short: While onion sets are the standard for convenience, starting from seed offers superior disease resistance and a wider variety of choices. By using a multisow technique, you can produce impressive yields from a small footprint, transforming how you approach your vegetable plot with a simple, reliable, and productive method.

Onions are a staple of the vegetable garden, prized for their versatility and storage potential. While many gardeners rely on sets—immature bulbs planted directly into the soil—these can be prone to bolting, where the plant prematurely produces a flower, diverting energy away from the bulb. Heat-treated sets can mitigate this risk, but growing from seed provides a robust alternative. Seeds are generally more economical and offer a significantly broader range of varieties, allowing you to select for specific flavours, colours, and storage qualities.

The multisow method, championed by practitioners like Charles Dowding, involves sowing three or four seeds per module rather than individual plants. This technique is highly efficient; in a no-dig garden, just eight modules can yield over 12kg of bulbs alongside a secondary harvest of spring onions. When these multisown clumps are ready for the ground, they should be planted as a single unit. This approach creates a cluster of bulbs that grow together, rather than being split into individual plants, which simplifies the process and maximizes space.

Success with onions requires careful timing and site preparation. Whether starting indoors from mid-winter to early spring or sowing directly outdoors once the soil warms, the goal is to have strong, healthy plants by late spring. Lengthening days trigger bulb formation, so the more leaves a plant has by that time, the larger the final bulb will be. A sunny, well-drained site is essential, and incorporating organic matter—such as compost or well-rotted manure—into the soil before planting provides the necessary nutrients and moisture retention for a thriving crop.

For those looking to extend their season, overwintering varieties can be sown in late summer or early autumn. These Japanese types are specifically bred to withstand colder temperatures, which would otherwise trigger bolting in standard varieties. By choosing varieties with an Award of Garden Merit, gardeners can ensure they are working with reliable, high-performing stock that has been vetted for disease resistance and consistent cropping.

General information, not professional advice. Spotted an error? Flag the card or see corrections and complaints.

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