Working with Onion Transplants
Onion transplants may need special care when first planted in the ground. Here are some techniques to keep in mind.
Hardening off transplants is simply getting them used to being outdoors instead of in a warm house. Plants are like people - they can get sunburned, windburned or chilled. To harden off your seedlings, take your flats outside around the time of the average last frost in your area. Set them in partial shade, protected from wind, for a couple of hours the first day. Increase their time outside by an hour or so a day the first week.
Next, place the flats in full sun for most of the day, and if there's no danger of frost, leave them out overnight. If you suspect a freeze, bring them in or protect them well outside.
After a week to 10 days of gradual exposure to the outdoors, your plants will be tough enough to take the shock of transplanting.
Remember: Onion plants are more tender than sets, so transplant after the danger of hard freezes in your area has passed. Light frosts won't hurt them, though.
Before you plant your seedlings, work compost or fertilizer into your soil, then smooth the surface. Putting the transplants in is easy: Lay the plant on your index finger, and push your finger with the onion on it about two inches into the soil. Lift up your finger and the onion just a bit (this gets the roots headed in the right direction), then slide your finger out of the hole and firm the soil around the plant. (You can also use a pencil to make the holes for the plants.) Don't be afraid to transplant small seedlings - even those as small as toothpicks. Even tiny ones can make it.
Direct-Sowing Onion Seed
Sowing onion seeds right into the garden can allows you to skip some transplanting steps. Here's how it's done.
Combine the onion seed with some radish seed (about 5% radish seed) and sprinkle or "broadcast" this mixture in a wide row about 15 inches across. Don't worry too much about spacing - as you harvest the fast-growing radishes (they also serve as row markers) and young onions for early eating or pickling, you'll create plenty of space between the remaining onions for them to grow to full size.
To make sure the seed has good contact with the earth, spread a light layer of soil on top of the seed and firm it into the soil by tamping it down with a hoe or rake.
Young Plant Care
When the plants are about 1/4 inch high, thin out some of them with a steel garden rake. You may feel cruel doing this the first time, but do it. The end results will be worth it. Just drag the rake lightly through the onion row. The teeth thin out some of the plants, and also cultivate within the row, uprooting many little weeds as well.
When the bulbs reach the size of a marble or walnut (1/2 to 1/4 inch in diameter), you can pull some of them to use right away for pickling or boiling. The small white onions are best for canning, pickling and boiling. 'Crystal Wax' and 'White Portugal' are two good small white onions to grow. Sow them close together in April or May after preparing the soil as you would to grow big onions.
For storage onions, try growing 'Early Yellow Globe', a convenient, all-around cooking size. Plant the seeds fairly thickly and give the seedlings a really good thinning by dragging a rake through the row once they've sprouted. When the onions have developed a good top growth, pull up some and eat them as scallions. Your aim is to harvest enough to eat as scallions to leave the remaining plants at a spacing of three to four inches apart.
You can gain a week or more on the onion season by soaking the seeds in lukewarm water for a few hours before planting them.
Another way to sprout the seeds is to spread them on a wet paper towel and roll up the towel. Then put it on a damp terrycloth towel and roll that up. Put the towels in a plastic bag and seal it. Check it after four or five days. When the sprouts are tiny, plant them just as you would onion seeds.