Starting onions from seed offers gardeners in the UK a cost-effective and rewarding way to grow fresh, flavorful onions, adapting perfectly to the region’s climate and soil conditions with the right approach.
Growing Onions from Seed in the UK
Success begins with choosing the right onion variety suited to UK weather—common types include Yellow, Red, and Sweet onions. Sow seeds indoors from late winter to early spring, around February to March, in seed trays with well-drained, nutrient-rich compost. Maintain temperatures between 10-20°C and keep soil consistently moist but not waterlogged. Thin seedlings when they reach 5 cm to ensure healthy, spacious growth.
Optimal Soil and Sunlight Conditions
Onions thrive in full sun exposure and well-aerated, sandy-loam soils with a pH of 6.0 to 7.0. Pre-soaking seeds for 12 hours can improve germination rates. For UK gardens, raised beds or deep containers reduce waterlogging risks and improve root development, critical for strong onion bulbs.
Transplanting and Ongoing Care
Once seedlings develop true leaves and reach 10 cm tall, transplant outdoors after hardening off for 7–10 days. Space plants 10–15 cm apart in rows with 30 cm between rows for airflow. Water deeply but infrequently to encourage deep root growth, and apply organic mulch to retain moisture and suppress weeds throughout the growing season.
With careful planting, consistent care, and attention to local conditions, growing onions from seed in the UK delivers a successful harvest. Start your journey today—enjoy fresh, homegrown onions that elevate your kitchen and garden alike.
Onions can also be grown from seed, although this takes a little more time and care. A warm, sunny spot in well-drained soil is ideal for growing onions, they can also be grown in large containers. Learn how to grow onions from seed in the UK with this comprehensive guide.
Discover tips for sowing, caring, and harvesting for a fresh and flavorful onion crop. Onions are easy and cheap to grow, both from seed and from heat-treated sets. Follow our step-by-step guide, below, to growing onions from seed (skip to Step 3 for instructions on planting out sets).
Everything you need to know about Growing Onions from Seed in the UK (with a focus on Heirloom Varieties) Introduction: Seeds vs. Sets - Why Choose Seeds? As a seed saver and seed seller, I feel I need to declare my strong bias for growing onions from seed. When you grow onions from seed you have a much more exciting range of varieties available to you.
Learn how to grow onions from seed in the UK, including choosing varieties, preparing soil, and overcoming common challenges. Get expert tips on successful onion cultivation and harvesting. Discover how to grow onions in the UK with our beginner-friendly guide.
Learn when to plant sets or seeds, the best soil and care tips, and how to harvest. Clear, expert and practical advice on how to grow top class onions from seed. When and how to sow seeds, best soil conditions and sowing onions in pots.
Onions, or Allium cepa as they are botanically named, are a staple of home-growers and can be grown either from seed or from sets, which are simply small onion bulbs that have already been grown from seed. Growing onions from seed can be very rewarding, but patience is required as the crop will take time to mature and generally only be harvestable after 100. How to Grow Onions from Seed When To Sow: Jan-February (Indoors); March-April (Direct) Harvest: August-September Germination: 7-14 days Full Sun Starting Indoors: Onion seed can be notoriously tricky to germinate and, as a result, many growers choose to start their onions inside in flats.
Use light, well-draining compost or seed starter, sowing seeds at a depth of 1cm (½"). Cover lightly with. Which? Gardening experts reveal how to grow your own onions and the best varieties.
We explain exactly what jobs to do to get great crops of onions and how to grow them from seeds and sets.