Onions are a kitchen staple used in everything from soups and stews to salads and stir-fries. But did you know you can grow onions indoors—even without a garden?
Whether you’re limited by space, weather, or simply want fresh produce at your fingertips, learning how to grow onion indoors is easier than you might think.
With just a sunny windowsill, the right containers, and a few basic tools, you can enjoy a steady supply of green onion tops or even small onion bulbs all year long.
In this step-by-step guide, we’ll cover how to grow onions indoors in 8 easy steps—from choosing the right type to harvesting your crop.
We’ll also explore the best soil mix, watering techniques, light requirements, and common mistakes to avoid.
Whether you’re growing green onions (scallions) or full bulb onions, this guide has everything you need for success.
Why Grow Onions Indoors?
Growing onions indoors has several benefits:
- Fresh onions year-round without relying on the grocery store
- Space-saving for apartments, small homes, or urban gardens
- Pest-free environment compared to outdoor growing
- Quick results with green onions ready in just weeks
- Fun and educational project for kids and beginners
Plus, you can start with store-bought onion sets or even kitchen scraps!
How To Grow Onion Indoors in 8 Easy Steps
Step 1: Choose the Right Type of Onion
There are several ways to grow onions indoors, but your first step is deciding what kind of onion you want to grow:
- Green onions (scallions): Fastest and easiest to grow. You can regrow these from kitchen scraps or seeds.
- Bulb onions: Takes longer but possible indoors with the right pot size and conditions. Choose smaller varieties like shallots or short-day onions for better indoor performance.
You can grow onions from:
- Seeds
- Seedlings (starts)
- Sets (small dormant bulbs)
- Sprouting onions or onion bottoms from your kitchen
For beginners, onion sets or green onion scraps are the easiest and fastest method.
Step 2: Select the Right Container
Onions have shallow roots, but they still need room to grow.
Here’s what to look for:
- Depth: At least 4–6 inches deep for green onions; 8–10 inches for bulb onions
- Drainage: Make sure your pot or container has drainage holes
- Material: Plastic, clay, fabric, or recycled containers all work
For green onions, you can even use:
- Window boxes
- Mason jars (for hydroponic regrowth)
- Plastic cups with drainage holes
Growing bulb onions? Use a wider pot to space them 3–4 inches apart.
Step 3: Use the Right Soil Mix
Onions grow best in light, loose, and well-draining soil.
Use:
- Potting mix (not garden soil, which is too heavy)
- Add 20–30% perlite or sand to improve drainage
- Mix in some organic compost or worm castings for nutrients
pH should be slightly acidic to neutral (6.0 to 7.0). Avoid overly wet or compacted soil, which can cause rot.
Step 4: Plant Your Onions
For onion sets or bulbs:
-
Place the flat root side down in the soil.
-
Cover with 1–2 inches of soil.
-
Space them about 3 inches apart.
For green onion scraps:
-
Cut the white root ends with at least 1 inch of stem.
-
Soak them in water overnight.
-
Plant upright in soil, just covering the roots.
For seeds:
-
Plant ¼ inch deep and lightly cover with soil.
-
Keep the soil moist and warm (65–75°F) for germination.
-
Thin seedlings once they reach 2–3 inches tall.
Water gently after planting.
Step 5: Place in a Sunny Location
Onions are sun-loving vegetables.
Indoors, they need:
- At least 6–8 hours of direct sunlight daily
- A south-facing windowsill or balcony is ideal
- If sunlight is limited, use a grow light for 12–14 hours per day
Lack of light is the main reason onions fail to grow indoors. Use full-spectrum LED grow lights for best results if you’re growing in winter or low-light areas.
Step 6: Water and Feed Properly
Keep the soil consistently moist but not soggy.
Here are watering tips:
- Water when the top 1 inch of soil feels dry
- Avoid overwatering, especially in cooler indoor conditions
- Use a spray bottle or watering can with a narrow spout
Fertilizing Tips:
- Feed every 2–3 weeks with a balanced liquid fertilizer (such as 10-10-10)
- For green onions, use a nitrogen-rich fertilizer to promote leafy growth
- Stop fertilizing bulb onions about 4 weeks before harvest
Indoor containers dry out faster than outdoor soil, so monitor moisture closely.
Step 7: Monitor Growth and Prune as Needed
Onions are low-maintenance, but regular observation helps.
Watch for:
- Yellowing leaves (could indicate overwatering or nutrient deficiency)
- Slow growth (may need more light or fertilizer)
- Pests like aphids (rare indoors but treat with neem oil if needed)
For green onions:
- Begin harvesting once leaves are 6–8 inches tall.
- Cut above the white base to allow regrowth.
For bulb onions:
- As bulbs grow, push soil away slightly to expose the top.
- Stop watering when tops begin to yellow and fall over, indicating maturity.
Step 8: Harvest and Store Your Onions
Green Onions:
- Ready in as little as 2–3 weeks.
- Cut the green tops and allow regrowth for multiple harvests.
Bulb Onions:
- Harvest after 90–120 days (depending on variety).
- Tops will yellow and collapse.
- Gently pull bulbs from the soil.
- Cure in a dry, well-ventilated place for 2–3 weeks before storing.
Storage:
- Store green onions in the fridge or regrow them again.
- Keep cured bulb onions in a cool, dry, dark place.
- Avoid plastic bags—use mesh or breathable containers.
Bonus Tips for Growing Onions Indoors
- Rotate pots regularly for even sun exposure.
- Use companion planting like growing herbs nearby to deter pests.
- Start new batches every few weeks for a continuous supply.
- Try hydroponic methods for growing green onions in water only.
Common Mistakes to Avoid
- Not enough light: Leads to weak, spindly growth
- Overwatering: Causes root rot or bulb rot
- Crowding plants: Reduces airflow and bulb size
- Poor drainage: Always use pots with holes and well-draining soil
- Starting with treated grocery onions: Choose organic or certified disease-free onions
Learning how to grow onion indoors in 8 easy steps is a great way to take control of your food supply, reduce waste, and enjoy fresher flavors in your cooking.
Whether you’re regrowing scallions from scraps or cultivating full bulb onions in pots, this indoor gardening project is low-cost, fun, and highly rewarding.
With proper light, water, and care, you can grow healthy, delicious onions indoors year-round—even if you’ve never grown anything before.
Start small, experiment, and enjoy the satisfaction of harvesting homegrown onions right from your kitchen window
