Onion Growing Guide Crop Rotation Group Allium (Onion family) ● Soil Fertile, well drained soil with compost dug in. In clay soil, grow in raised beds or rows. Position Sun or partial shade. Frost tolerant Yes. Feeding Not normally required, though can be given a liquid feed in spring. Companions Beetroot, Tomato, Lettuce, Chamomile and Flax. Jane recommends Beetroot, Lettuce, Cabbage, Strawberry. Spacing Single Plants: 15cm (5") each way (minimum) Rows: 10cm (3") with 20cm (7") row gap (minimum) Sow and Plant Sow seeds in early autumn to plant out in late autumn Our Garden Planner can produce a personalised calendar of when to sow, plant and harvest for your area. Notes Onions will only start bulbing when the days become long enough to expose them to enough light Harvesting Harvest as soon as they reach a reasonable size. If storing them, wait until the tops start to die down and dry for about 10 days. Troubleshooting Weed early and often to keep onions growing strong. Planting and Harvesting Calendar < Back to All Plants Pests which Affect Onion Allium Leaf Miner Aphids (General) Millipede Onion Root Fly Slug Snail Plant Diseases which Affect Onion Allium White Rot Onion Downy Mildew Onion Fusarium Basal Rot