This post contains affiliate links. This means I may earn a small commission if you make a purchase through these links, at no additional cost to you. As an Amazon Associate (or other affiliate program), I earn from qualifying purchases. I only recommend products I personally use and love. Thank you for supporting Grown on a Hill!

Why It’s Worth the Effort

When it comes to growing onions, many gardeners opt for sets—a quick and convenient method. However, starting onions from seed offers unique advantages that make it worth the extra effort. From a wider variety of choices to healthier, more robust plants, starting from seed ensures a rewarding experience and a bountiful harvest. In this post, we’ll explore the benefits of growing onions from seed, walk through the seed selection process, and provide step-by-step instructions to get your onions off to a strong start.

Why Grow Onions from Seed?

Growing onions from seed may require more time and planning, but the benefits far outweigh the effort. From broader variety options to improved yields, here's why it's worth considering:

Better Yields and Larger Onions

Through personal experience, seed onions have consistently produced larger bulbs and higher yields compared to onions grown from sets. This is likely because seeds allow onions to develop a robust root system from the start, leading to healthier and more productive plants.

Access to a Wider Variety of Onions

Onion sets are often limited to a small selection of yellow, red, and white varieties. Seeds open up a world of possibilities, including sweet, pungent, and heirloom onions, such as Walla Walla, Red Burgundy, or Ailsa Craig.

Stronger, Healthier Plants

Onions started from seed are less prone to bolting (premature flowering) and tend to store better. They adapt to their growing environment right from germination, resulting in resilient plants that thrive throughout the season.

Cost-Effective and Sustainable

A single packet of seeds can yield hundreds of onions, making it an economical choice compared to sets. Plus, seed-grown onions can often be saved for future planting, further reducing costs.

Choosing the Right Onion Seeds

Selecting the right onion seeds is crucial for success. Here are some tips to guide your decision:

Understand Your Growing Zone

Onions are categorized as long-day, short-day, or day-neutral varieties.
Long-day onions require 14-16 hours of daylight, making them ideal for northern regions.
Short-day onions thrive in southern areas with 10-12 hours of daylight.
Day-neutral onions are versatile and grow well in most regions.

Decide on Onion Types

Yellow Onions: Great for cooking, versatile, and long-storing varieties include Yellow Sweet Spanish and Patterson.
Red Onions: Perfect for fresh use in salads, sandwiches, or grilling; try Red Baron or Ruby Ring.
Sweet Onions: Known for their mild flavor, varieties like Vidalia and Candy are excellent for eating raw or caramelizing.

Look for Disease-Resistant Varieties

Choosing disease-resistant seeds helps prevent common issues like onion downy mildew or white rot.

Consider Your Harvest Goals

If you’re aiming for storage onions, look for varieties noted for their longevity. If you prefer fresh onions for immediate use, opt for sweeter, softer varieties.

Step-by-Step Guide to Sowing Onion Seeds Indoors

Starting onions indoors gives them a head start, ensuring they’re ready to transplant once the weather warms. Follow these simple steps to grow onions successfully from seed.

Step 1: Gather Your Tools and Supplies

Before you begin, ensure you have the right tools and materials:

High-quality onion seeds
Seed-starting trays or shallow containers with drainage holes
Seed-starting mix (light, fine-textured, and nutrient-rich)
Plant labels and a marker
Spray bottle or watering can with a fine nozzle
Heating mat (optional, for consistent warmth)
Grow lights or a sunny windowsill

Step 2: Prepare Your Seed-Starting Mix

Choose a seed-starting mix rather than regular garden soil. A light, airy mix ensures good drainage and prevents seedling diseases like damping-off.
Moisten the mix with water until it feels like a damp sponge—not soggy.

Want to learn how to make a seed-starting mix? The Perfect Seed-starting Mix

Step 3: Fill and Label Your Trays

Fill your trays or containers with the moistened seed-starting mix, leaving about 1/2 inch of space at the top.
Use plant labels to mark the onion variety and sowing date. This step is especially important if you’re growing multiple varieties.

Step 4: Sow the Seeds

Make shallow furrows about 1/4 inch deep in the seed-starting mix. You can use a pencil or your finger to create straight rows.
Space seeds about 1/2 inch apart in the furrows to avoid overcrowding.
Lightly cover the seeds with a thin layer of seed-starting mix and gently press it down.

Step 5: Water and Cover

Mist the soil surface with a spray bottle to evenly moisten it without disturbing the seeds.
Cover the trays with a clear plastic dome or plastic wrap to retain humidity. This creates a mini greenhouse effect that encourages germination.

Step 6: Provide Warmth and Light

Place the trays in a warm location, ideally between 65-75°F. A heating mat can help maintain consistent temperatures.
Once the seeds germinate (in 7-14 days), remove the plastic cover and place the trays under grow lights or near a sunny window.

Onions need 12-16 hours of light per day. Use a timer to automate the lighting schedule.

Step 7: Thin the Seedlings

When seedlings reach 2-3 inches tall, thin them by snipping the weaker plants at the soil line, leaving about 1 inch of space between the strongest seedlings. This prevents overcrowding and ensures healthy growth.

Step 8: Maintain and Harden Off

Water seedlings consistently, keeping the soil evenly moist but not waterlogged.
Once seedlings are 4-6 inches tall and the outdoor soil is workable, begin hardening them off by gradually introducing them to outdoor conditions. Start with 1-2 hours of outdoor exposure per day, increasing the time over a week.

Why January/February is the Best Time to Start Onion Seeds

Onions have a long growing season, making January or February the ideal time to start seeds indoors. By giving your onions an early start, you’ll have well-established seedlings ready for transplanting when the weather warms in spring. This timing ensures larger, healthier bulbs at harvest.

Final Thoughts

Starting onions from seed requires patience and care, but the rewards are significant. You’ll enjoy a greater variety of onions, stronger plants, and better storage options. By following these steps and tips, you’ll set yourself up for a successful onion-growing season. Whether you’re growing sweet, pungent, or specialty varieties, the effort you invest in January or February will pay off in a flavorful, abundant harvest.

Featured