Dear Aggie: Seed Onions | Agriculture

Dear Aggie: I usually grow onions from seedlings, but I heard you can grow them from seed. What are the benefits of seeds – and are they easy to grow this way?

A: Yes, onions are easy to grow from seed. Like you, I used to grow onions from sets, but switched entirely to onions from seeds and transplants. I find onions grown from seeds grow bigger and keep better than those grown from sets.

Onions are biennial plants. The first year they grow from seed in a bulb. After experiencing the cold of winter, the bulb begins to grow again in the spring to produce a flower spike during the summer. When you start with sets, your onions are already in the second year of their growth cycle. The energy that would otherwise go into the bulb is directed towards flowering. As the bulbs are at the end of their growth cycle, they are more likely to sprout and rot during storage.

In commercial farming, onions are usually sown directly in fields. Because onions compete poorly with weeds, especially in the seedling stage, commercial growers often use selective herbicides to control weeds. Less frequently (due to labor costs), commercial growers will start seed in cold frames, greenhouses, or beds and then transplant it into the field.

In the vegetable garden, direct sow the onions in a well-drained bed free of weed seeds. Raised beds are ideal. Onions are good for intercropping with other garden plants, especially early maturing spring vegetables. Sow the seeds when the soil reaches 50 F. Plant the seeds ¼ inch deep, ½ inch apart, in rows 12 to 18 inches apart. Thin to 4 inch spacings for large bulbs, 2 inch spacings for smaller bulbs but higher yields, or 1 inch spacings for scallions.

Direct seeding in a home garden often means a lot of weeding by hand. This can be tricky because onion plants are tiny and hard to see. Also, direct seeding in the garden may not allow long-season varieties enough time to mature. For this reason, I limit direct seeding to scallions (otherwise known as spring onions, which are harvested before the bulb forms). For my main season onion harvest, I plant grafts instead.

Start transplants indoors under grow lights or in a greenhouse about 8-10 weeks before the last frost date. Plant 4 or 5 seeds in each cell, or sow in flats ¼ inch deep and ½ inch apart. If the tops grow too tall and start to sag, cut them back to about 3 inches tall with scissors. After hardening, transplant 2 to 4 weeks before the last frost date. Space 4 inches apart for large bulbs or 2 inches apart for small bulbs.

If you forget to plant onion seeds in the spring, you can purchase graft packets from commercial growers by mail order. Some local nurseries also offer bunches of onions. Another option is to grow pearl onions – which can also be used as sets the following spring. Sow the seeds liberally in a block in mid-summer. About 2 months after planting, lower the tops, forcing the plants to form small bulbs. Once the tops are dry, cut them off leaving about ½ inch of stem. Harden and store in a cool, dry place as you would any other onion for storage.

Finally, the most important thing to do when selecting onion seeds and transplants is to select the right variety for our latitude and day length. Here in upstate New York, select only long-day varieties.

Written by Michael Shane Nuckols, Agriculture and Natural Resources Manager

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