Onion Growing Tips: Best Practices for Healthy Bulbs in UK Gardens

When you grow onions, a hardy, bulb-forming vegetable that thrives in cool climates and stores well for months. Also known as bulb onions, they’re one of the most reliable crops for UK gardens, whether you’re planting in spring or autumn. Unlike fancy vegetables that need perfect conditions, onions just want good soil, enough sun, and a little patience. They don’t need fancy feed or constant watering—just the right start and a clear plan.

What makes onions tricky isn’t the plant itself, but the timing, the exact window when you plant determines if you get small bulbs or big, store-ready ones. In the UK, planting in early spring (late February to March) gives you the best chance for large bulbs. If you plant too late, the onions will focus on leaves instead of bulbs. The soil, a loose, well-drained mix rich in organic matter but low in fresh manure is just as important. Heavy clay? Mix in sand and compost. Acidic soil? Add a bit of lime. Onions hate wet feet and sour ground—they’ll rot or stay tiny if you get this wrong.

You’ll also need to think about spacing, how far apart you plant each onion sets or seedlings. Crowding them leads to small bulbs and disease. Give each plant at least 10cm of space. Mulch lightly with straw to keep weeds down and moisture steady—onions have shallow roots and can’t compete with weeds. Watch for onion fly and thrips; a row of companion plants like carrots or lettuce helps keep pests away. And don’t fertilize after midsummer—let them mature naturally.

The posts below cover everything you need to make your onions grow big and sweet. You’ll find guides on soil prep that actually works in British gardens, the exact months to plant based on your region, how to avoid the most common mistakes, and even how to store them so they last through winter. No fluff. No theory. Just what you need to get a harvest you can actually use.