The easiest way to grow onions at home is from sets. But there are many interesting onion varieties that can only be bought as seeds!
Onion seeds don’t have the best germination rate. Fortunately, how many onion seeds per hole you plant has little impact on how easily you can separate the bulbs when they sprout!
To guarantee a large onion crop, plant at least 2 seeds per hole. Or sow seeds in dense rows to be thinned out later.
Types Of Onions For Your Garden
At the grocery store, onions are categorized based on things like color, size, and flavor.
Classic bulb varieties include red, yellow, and white onions. You can also grow sweet onions, which contain less sulfur and have a very mild flavor.
Another bulbous onion variety is the shallot. If traditional onions tend to pack too much “heat” for your taste buds, shallots are a more delicate alternative.
Leeks and green onions (scallions) do not produce large bulbs. Instead, they are grown and harvested for their flavorful foliage.
Short-Day Vs. Long-Day Onions
Garden onions are generally labeled as short- or long-day depending on how much daylight they require to produce bulbs. There are also some day-neutral varieties.
Short-day onions form bulbs when receiving 10 to 12 hours of sun per day. In the United States, these varieties grow best in hardiness zones 7 and up.
Long-day onions need between 14 and 16 hours of sun per day. These varieties should be grown in hardiness zones 6 or colder.
Day-neutral onions grow best with 12 to 14 hours of sun a day. While these varieties are recommended for zones 5 and 6, they can technically be grown in all but the warmest climates.
Starting Onions From Seed Vs Sets
Onions can be started from seed or small bulbs called onion sets.
Onion seeds tend to be the preferred method. Some of the advantages of starting onions from seed include:
- You can purchase seeds of countless varieties (sets are only available for a few types of onion)
- Onions grown from seed are less likely to go to bolt (flower early)
- Onion seeds are less expensive than sets
The main drawback of growing onions from seed is that they must be started indoors in very early spring in most climates.
Onion sets are a great option for gardeners who want to grow onions quickly. Since onion sets mature within about 14 weeks, you can start onions well after the risk of frost has lifted.
How To Start Onions From Seed
The best time to start onion seeds indoors is at least 8 to 10 weeks before your last frost date. However, some gardeners opt to start onions as early as 12 weeks before their last frost.
Plant onion seeds ¼-inch deep in a tray filled with seed-starting mix.
Place trays in a warm location and keep the soil moist while you wait for the seeds to germinate. Germination may take a couple of weeks. However, don’t be surprised if you see sprouts within a few days!
Can You Direct-Sow Onion Seeds Outdoors?
In colder climates, there is not enough time between the harsh winter and hot summer for onions to form healthy bulbs.
In warmer climates, however, it may be possible to plant onion seeds in the fall! With this strategy, the onions grow throughout the mild winter and are ready for harvest in mid-spring.
How To Transplant Onion Seedlings
Onion seedlings can tolerate light frost. It’s usually safe to transplant onion seedlings just before your area’s last frost date.
When it’s time to transplant your onion seedlings, start by gently separating the bulbs. Seeds started in cells are easiest to separate.
Don’t plant your onions too deep! While you should loosen the several inches of soil prior to transplanting to encourage healthy bulb growth, onion seedlings should only be planted 1 inch deep.
Proper spacing depends on the type of onion and when you plan to harvest them.
For a crop of mature onions, space seedlings 4 inches apart.
If you want to harvest young green onions throughout the season, space seedlings 2 inches apart. Harvest every other onion partway through the season, allowing the rest to fully mature.
Alternatively, you can grow clusters of onions by transplanting entire cells without separating the bulbs. Space clusters 6 inches apart.
Tips For Growing Onions
Onions are full-sun vegetables and need at least 6 hours of direct sunlight per day. Most varieties, however, prefer 8 to 10 hours of sun a day.
Adequate sunlight is extremely important when growing bulb onions. Green onions can tolerate less light but still grow best in full sun.
All types of onions grow well in containers. You can easily cultivate onions on a balcony or patio.
Since the bulk of an onion's growth occurs below the soil, they are a wonderful candidate for companion planting with other vegetables.
Plant onions in well-draining, fertile soil with a neutral pH.
Loose soil is a must when growing bulb onions. If the soil around your seedlings is compacted, the bulbs will be unable to expand.
Supplement the soil with aged compost or granular fertilizer prior to transplanting onions to the garden. Most onions respond best to high-phosphorus fertilizers.
Onion seeds germinate when the soil temperature is above 40°F. The ideal temperature for germination is 75°F.
While onions can tolerate frost and heat, most growth occurs when the temperature is between 55°F and 75°F. This is why it’s important to start onion seeds well before summer temperatures arrive.
Onions thrive in moist soil. Consistent moisture is essential for proper germination and growth.
With that said, you should never let your onion plants sit in soggy soil!
For the best results, water the top inch of soil around your onions once per week. Adjust this schedule as needed for excessive heat or rain.
Saving Onion Seeds
Onions are biennial plants. An onion's complete life cycle occurs over 2 years, with flowering and seed production happening in the second year.
If you want to save onion seeds for future planting, you’ll need to store selected bulbs through winter and then replant them the following spring. Otherwise, saving onion seeds is mostly just a waiting game!
Onions typically go to seed in the late summer of their second year. Wait for the seed head to dry before collecting seeds — mature seeds may start dropping on their own.
Set collected onion seeds out to dry for several days before storing them in a paper envelope or seed box.
Onion seeds remain viable for around 2 years in storage.
How Many Onion Seeds Per Hole – Final Thoughts
Onions may not have a reputation as the easiest vegetable to grow from seed. But starting onion seeds at home is much simpler than most amateur gardeners believe!
The key to a healthy onion harvest is starting the seeds indoors. It’s also important to not be stingy when planting seeds since many onion seeds fail to germinate.