How to Start Seeds Indoors: The Ultimate Guide 🌱

Starting seeds indoors is more than a fun gardening project — it’s a strategic way to gain control over your growing season, experiment with rare or heirloom varieties, and nurture strong, healthy seedlings that are ready to thrive outdoors.

Whether you're growing tomatoes in Toowoomba, chillies in Canberra, or pansies in Perth — this guide walks you through every stage, with real seed examples from The Seed Vault, plus deep dives into lighting, temperature, and troubleshooting for success.

🌏 Why Start Seeds Indoors?

Indoor sowing isn’t just for cold climates — even in warmer parts of Australia, it offers huge benefits:

• Extend your growing season: Start summer crops like tomatoes and capsicum in late winter or early spring to beat the garden centre rush.

• Grow rare or hard-to-find plants: Heirlooms like Tomato ‘Green Zebra’, Capsicum ‘Purple Beauty’, or Lettuce ‘Freckles’ aren’t always available as seedlings.

• Avoid pests and harsh weather: Early seedlings are protected from slugs, wind, heavy rain, and extreme UV.

🛠 What You’ll Need (With Seed Examples)

🧬 Choosing the Right Seeds to Start Indoors

Not all seeds are suited for indoor starting. Some grow better when direct sown outdoors.

✅ Best seeds for indoor sowing:

Vegetables

• Tomatoes – Start 6–8 weeks before last frost.

• Capsicums – Loves warmth. Needs heat to germinate.

• Eggplant – Slow grower. Needs heat mat and good light.

• Broccoli ‘Green Sprouting’ – Cool-season veg that transplants well.

• Lettuce ‘Cos’ – Quick to germinate. Easy indoors in early autumn or spring.

Herbs

• Basil ‘Genovese’ – Easy to start on a warm windowsill.

• Parsley – Slow germinator, so patience is key.

• Chives – Compact, great for pots or windowsills.

Flowers

• Pansy ‘Regal Ruffles’ – Likes cooler conditions. Surface sow.

• Lobelia – Tiny seeds. Best sown on the surface and misted gently.

• Dianthus – Hardy and good for transplanting.

🚫 Seeds better sown directly into the garden:

• Root crops: Carrot, beetroot, radish – dislike transplanting.

• Fast growers: Corn, zucchini, cucumber – grow so quickly indoors that timing gets tricky.

• Legumes: Beans, peas – don't like root disturbance.

📆 When to Start Seeds Indoors (Australia)

Timing depends on your location and the seed variety. Here’s a rough guide:

📌 Example: In Melbourne, start tomatoes and capsicums indoors in mid-August, and move them outside in late October when frost risk is gone.

🌡️ Heat Mats: Are They Worth It?

Yes — especially if you’re sowing heat-loving plants like chillies, capsicum, or eggplant in winter or a cool climate.

What a heat mat does:

• Keeps soil consistently warm (21–27°C ideal for most warm-season crops)

• Speeds up germination — some seeds emerge in 3–5 days vs 10–14 days without

📌 Example: Capsicum can take 2+ weeks to germinate at room temp (~18°C), but only 5–7 days on a heat mat set to 25°C.

💡 Grow Lights: Do You Need Them?

If your seedlings are stretching, leaning, or growing pale, you absolutely need more light. Even a north-facing window isn’t always enough in winter.

Types of grow lights:

• LED panels – Energy-efficient, cool, long-lasting

• T5 Fluorescent tubes – Budget-friendly, good for shelves

• Full-spectrum LEDs – Best for seedlings and mature indoor plants

How to use grow lights:

• Position lights 10–15 cm above seedlings

• Run lights for 14–16 hours/day

• Use a timer to keep schedule consistent

📌 Example: Tomato seedlings will grow tall and weak if light is too far away or inconsistent. Under grow lights, they stay compact, green, and strong.

🌱 Sowing Your Seeds: Step-by-Step

1. Fill trays with pre-moistened seed raising mix.

2. Sow seeds at the correct depth:

   • Large seeds: 10mm deep (e.g. tomato, broccoli)

   • Tiny seeds: surface sow (e.g. lobelia, pansy)

3. Mist gently with water.

4. Cover with plastic wrap or a humidity dome to trap warmth and moisture.

5. Place in a warm spot (or on a heat mat) until germination.

🌞 After Germination: Light, Water & Care

• Remove covers as soon as seedlings appear.

• Provide strong light daily (sun or grow light).

• Water from the base or mist when top feels dry.

• Thin out weaker seedlings once true leaves form (use scissors, don’t pull).

🌬️ Hardening Off: Prepare for Outdoors

A critical but often skipped step!

1. Start 7–10 days before transplanting

2. Place trays outdoors in dappled shade for a few hours

3. Gradually increase exposure to sun and wind

4. Protect from strong wind, rain, or cold nights

5. Transplant when seedlings are sturdy and weather is stable

🐛 Common Mistakes to Avoid

🎉 Final Thoughts

Growing from seed is empowering, exciting, and surprisingly addictive. With the right setup — a bit of warmth, light, and patience — you can raise a tray of strong, healthy seedlings ready to burst into life in your garden.

Browse our full collection of seeds to get started — and don’t forget to check out the rest of our Inside The Vault section for even more expert advice.

Happy gardening!
The Seed Vault