The best time to plant onions is generally in early to mid-spring when the soil starts to warm up and is workable. Here are some key points for planting onions:

• You can sow onion seeds outdoors from early to mid-spring, planting them about 1.3 cm (½ inch) deep in rows spaced 20-30 cm (8-12 inches) apart, thinning seedlings as they grow.
• Onion sets can be planted outdoors in prepared soil about 2 cm (¾ inch) deep so the pointed tip barely shows above the soil surface. Space sets 5-15 cm (2-6 inches) apart in rows 20-30 cm (8-12 inches) apart.
• In cases of wet or cold soil in early spring, onion sets can be started indoors and transplanted outside later.
• Onions prefer full sun and fertile, well-drained soil with a pH of 6.0 to 6.8.
• Onion seeds can also be started indoors 8-12 weeks before planting outside to give them a head start.
• If planting onion seeds indoors under grow lights, start them 10-12 weeks before planting and provide 10-12 hours of light daily to avoid early bulb formation.

Onions are hardy and can tolerate mild frost, and planting timing may vary by climate zone. Generally, soil temperature around 50°F (10°C) is favorable for planting onion sets. So, the main planting window for onions is early to mid- spring when soil conditions improve and temperature becomes suitable, but starting seeds indoors earlier is common for a better start. This information covers general onion planting guidelines for seeds and sets based on climate and soil conditions.