Onion Seeds

Onion Seeds FAQs

Take a look at some of the frequently asked questions we receive from those looking to buy Onion Seeds in the UK. You can contact our Customer Service Team or browse our general FAQs for further advice.

When should I plant onion seeds?

In the UK, onion seeds are typically planted in early spring, ideally starting indoors around February to March. This timing allows the seeds to germinate and develop into strong seedlings before being transplanted outdoors. Onions are hardy plants that can withstand cooler temperatures, so starting seeds indoors during late winter ensures they have a head start on the growing season. Transplant the onion seedlings outdoors once the soil has warmed up and all risk of frost has passed, usually around late March to early April. By following this planting schedule, you can give your onion plants the best chance of success and enjoy a harvest later in the year.

How do you grow onions from seed UK?

To grow onions from seed in the UK, start indoors in late winter, around February to March, by sowing seeds thinly in trays filled with seed starting mix. Transplant seedlings outdoors in early spring, once they have developed several sets of leaves and the soil has warmed up, typically in March to April. Choose a sunny location with well-draining soil and prepare the soil by incorporating organic matter. Plant seedlings about 4-6 inches apart in rows with 12-18 inches between rows, at the same depth they were growing in the trays. Keep the soil evenly moist, mulch to retain moisture and suppress weeds, and fertilise sparingly once established. Harvest onions when the tops turn yellow and fall over in late summer or early autumn, around August to September. With proper care, you can enjoy a successful harvest of fresh, flavourful onions grown from seed in your UK garden.

How long does it take to harvest onion seeds?

The process of harvesting onion seeds typically spans about two years. In the first year, onions are grown for their bulbs, which are harvested in late summer or early autumn. During the second year, some onion plants are allowed to overwinter, and in the following spring or early summer, they send up flower stalks. These flowers develop into seed pods containing onion seeds, which mature over several weeks to months. Once the seed pods turn brown and dry out, they are harvested and the seeds are extracted. The seeds are then air-dried further before being stored for future planting. Overall, the process from planting onion seeds to harvesting mature seeds involves allowing the plants to complete their full growth cycle, including overwintering and seed production, and typically takes about two years.

Why Grow Onions from Seed?

Growing onions from seed offers several advantages, including access to a wide variety of cultivars, cost-effectiveness, and the assurance of fresher and higher-quality produce. Starting from seed provides control over growing conditions and allows customisation of planting schedules. It also serves as a valuable learning experience, fostering self-sufficiency by enabling seed saving for future plantings. Overall, growing onions from seed is a rewarding journey, offering benefits ranging from cost savings to customisation and learning opportunities for gardeners of all levels.

Where can you grow Onions?

Onions can be grown in various areas of your garden, including garden beds, containers, raised beds, and even interplanted with other vegetables or herbs. Choose a sunny location with well-draining soil, and prepare the soil by incorporating organic matter such as compost. Garden beds offer flexibility in planting onions in rows or clusters, while containers are suitable for limited spaces like patios or balconies. Raised beds provide excellent drainage and soil aeration, and interplanting onions with other vegetables maximises space utilisation and pest deterrence. Additionally, cold frames or greenhouses extend the growing season for onions, allowing for earlier spring planting or later fall harvests. With proper care, onions can thrive and produce a bountiful harvest in various garden settings.

Why Buy Onion Seeds from Marshalls?

• Our customers are supported by a team of experts dedicated to providing valuable advice. You can also use our growing guides, backed by 70 years of experience, to get the best results from your onion seeds.
• You can contact us six days a week – including bank holidays – to discuss our products and services or to chat about all things gardening.
• We pride ourselves on offering fast delivery on all orders, with any 'in stock' plants and seeds sent out within three working days. We're green-fingered in more ways than one, too, thanks to our fully recyclable packaging.
• We won second place at the 2022 Great British Growing Awards for Best Online Retailer.
• Thousands of five-star reviews on Feefo and a 100% satisfaction guarantee on all our products show that we're a company you can trust.