Onions are a versatile and essential vegetable in every kitchen, and growing them from seed in the UK can be a truly rewarding experience. Whether you’re a seasoned gardener or a beginner, cultivating onions from seed is an excellent way to enjoy homegrown produce. Let’s explore the best way to start your onion seeds and ensure a healthy crop. When to Sow Onion Seeds In the UK, the timing of sowing onion seeds is crucial. Most onions are sown in mid- to late winter to give the plants a strong start before being transplanted outdoors. Indoor sowing: Start sowing onion seeds indoors in January or February. This gives your seedlings time to grow strong before planting them outside. Outdoor sowing: If sowing directly outdoors, wait until late March or early April, when the soil has started to warm up and is not too wet. Sowing Indoors To give your onions a good start, sowing indoors is highly recommended in the UK, especially for varieties that require a longer growing season. Step 1: Fill modular trays or pots with peat-free seed compost. Step 2: Sow seeds about 1cm deep, spacing them evenly in each module or pot. Step 3: Keep your seeds in a heated propagator or on a warm windowsill at temperatures between 10–16°C (50–60°F). Onions typically germinate within 1-2 weeks. Step 4: Once the seedlings are large enough, acclimatise them to outdoor conditions by gradually hardening them off over a couple of weeks before transplanting. Sowing Outdoors Onions can also be sown directly outdoors in the UK, but this should be done only after the soil has started to warm up in spring. Step 1: Choose a sunny, well-drained area with fertile soil. Add organic matter to improve the soil if needed. Step 2: Sow seeds 1cm deep in rows spaced about 20–30cm apart. Step 3: Thin out seedlings once they start to grow to ensure adequate space for each plant. Transplanting Onions When the seedlings are ready and the weather warms up, transplant them into the garden: Step 1: Space the seedlings 5–10cm apart, in rows 25–30cm apart. Step 2: Plant carefully to avoid damaging the young roots and water them in well. How to Sow Onion Seeds Onion seeds should be sown about 1cm deep, whether indoors or outdoors. When sowing indoors, modular trays are an efficient way to space your seeds. Outdoors, prepare your soil by ensuring it is well-draining and has adequate nutrients. How deep should I sow Onion Seeds? Onion seeds should be sown 1cm deep. When sowing outdoors, ensure the soil is not too wet to avoid the seeds becoming waterlogged, which can hinder germination. Onion Growing Requirements (Caring for Onions) Onion seeds should be sown 1cm deep. When sowing outdoors, ensure the soil is not too wet to avoid the seeds becoming waterlogged, which can hinder germination. Watering Onions need consistent moisture to grow well, but they don't like sitting in water. Water your plants during dry spells, but reduce watering once the bulbs begin to swell in mid-summer. Avoid overhead watering to prevent fungal diseases. Mulching Applying a layer of mulch around your onion plants can help retain moisture, suppress weeds, and maintain a steady soil temperature. Weeding Onions do not compete well with weeds, so keep the area around your plants clear. Be careful not to disturb the onion roots when weeding. Protection Onions can be vulnerable to pests and cold weather. Consider using row covers or fleece to protect your onions from the elements and keep pests away. Onion Growing Requirements (Caring for Onions) Onions are relatively pest-resistant but can still be affected by certain pests and diseases, including: Onion flies: Can damage bulbs. Use row covers or netting to prevent infestations. Downy mildew: Fungal disease that can be controlled by good air circulation and watering at the base of plants. Rust: A fungal disease that can be reduced by removing infected leaves and practicing good crop rotation. When & How to harvest onions Onions are typically ready to harvest when their foliage starts to yellow and topple over. This indicates that the bulbs have matured. Step 1: Gently lift the bulbs from the soil using a fork or by hand, being careful not to bruise them. Step 2: Allow the onions to dry in the sun for a few days before storing them. Storing Onions To store onions properly: Step 1: Once the onions are dry, store them in a cool, dry, and well-ventilated space. Step 2: Use net bags or slatted trays to keep them in a single layer. Check them regularly for signs of rot. Growing Success Tools To help you achieve success with your onion-growing efforts, consider these useful tools: John Innes Peat Free Seed Sowing Compost – Perfect for sowing onion seeds and promoting strong seedling growth. Kent & Stowe Stainless Steel Widger – Ideal for transplanting your onion seedlings with minimal root disturbance. Plantpak Half Seed Tray Kit x 10 – Great for starting onion seeds indoors and ensuring proper spacing for healthy growth. Sold out Sold out Sold out