To grow onions from seed indoors, start by planting them in a seed starting mix in late winter or early spring (February or March), ensuring proper depth and labeling.
Here's a detailed guide on how to successfully grow onions from seed indoors:
1. Timing is Key
- Start in late winter/early spring: February or March is ideal for most climates. This allows seedlings enough time to mature before transplanting outdoors.
2. Gather Your Supplies
- Onion seeds: Choose your desired onion variety.
- Seed starting mix: Use a fine-textured, sterile mix. Avoid garden soil, as it can harbor diseases.
- Containers: Seed trays, cell packs, or small pots work well. Ensure they have drainage holes.
- Watering can or spray bottle: For gentle watering.
- Grow lights (optional): Provide supplemental light for strong seedling growth.
- Labels: To identify the onion varieties you are growing.
3. Planting the Seeds
- Fill the container: Almost to the top with seed starting mix. Gently firm the surface.
- Create furrows: Make two furrows about 1/2 inch deep, spacing them adequately within the container.
- Sow the seeds: Sprinkle the onion seeds evenly in the furrows. Don't overcrowd them.
- Cover lightly: Cover the seeds with a thin layer of seed starting mix.
- Label: Label the container with the onion variety and date planted.
4. Providing the Right Conditions
- Water thoroughly: Gently water the soil until it is evenly moist, but not soggy.
- Maintain moisture: Keep the soil consistently moist until germination. You can cover the container with a plastic dome or plastic wrap to retain humidity.
- Provide warmth: Onion seeds germinate best at temperatures between 65-75°F (18-24°C). Use a heat mat if needed.
- Ensure light: Once seedlings emerge, provide plenty of light. Place them under grow lights or in a sunny window. Rotate the container regularly to prevent legginess.
5. Ongoing Care
- Water regularly: Keep the soil consistently moist, but allow the surface to dry slightly between waterings.
- Fertilize: Once the seedlings have their first true leaves, begin fertilizing with a diluted liquid fertilizer every 2-3 weeks. Follow the fertilizer instructions carefully.
- Thin seedlings: Once the seedlings are a few inches tall, thin them to allow for adequate spacing. Aim for about 1 inch between plants. You can transplant the thinned seedlings to other containers.
- "Haircut" Technique: Occasionally trim the tops of the onion seedlings to about 2-3 inches tall. This encourages stronger root growth and prevents them from becoming too leggy.
6. Hardening Off
- Acclimate to outdoors: About a week or two before transplanting outdoors, harden off the seedlings. Gradually expose them to outdoor conditions by placing them outside for a few hours each day, increasing the duration each day. Protect them from frost and strong winds.
7. Transplanting
- Prepare the garden bed: Choose a sunny location with well-drained soil. Amend the soil with compost or other organic matter.
- Transplant carefully: Gently remove the seedlings from their containers and plant them about 4-6 inches apart in rows.
- Water thoroughly: Water the transplanted seedlings well.
By following these steps, you can successfully grow onions from seed indoors, giving you a head start on the growing season and a bountiful harvest!
