- Exposure: Full sun
- When to plant: Fall in the warm climates, early spring in cold climates
- Pests and diseases to watch out for: Onion thrips, downy mildew
How to Plant Onions
Plant transplants about ½" deep and a few inches apart. (You can grow them from seed, but many onion varieties take a long time to mature, so seeding isn't always practical). Feed your transplants when you put them in the ground with a fertilizer that contains plenty of phosphorous for root development (look for something like 10-20-10). Water well.
- Short day (10 to 12 hours of daylight, generally grown in the south and planted in the fall for harvest in spring): Texas Super Sweet, Yellow Granex, Southern Belle Red
- Intermediate day (12 to 14 hours of daylight, grown in the Midwest and Central U.S. to Ohio): Candy, Red Candy Apple, Super Star
- Long day (14 to 16 hours of daylight, grown in the Northeast and Northern states): Candy, Copra, Red Candy Apple
NOTE: Mail-order transplants are your best bet if you want a specific variety; the "onion sets" you can purchase locally in some parts of the country are sold only as "yellow" or "white."
How to Care for Onions
After about three weeks in the ground, feed your onions again; this time, use a balanced fertilizer. Repeat every few weeks, but stop when the onions start to bulb, which is about two to three weeks before they're due to harvest; the bulbs also will start to push the soil aside (save your package instructions so you know generally when they'll be ready). Onions have shallow roots and like a steady supply of moisture, but don’t keep them soggy or they turn to mush. If you stick your finger in the soil to the first knuckle and you don’t feel moisture, it's time to water. Avoid overhead irrigation, which encourages foliage diseases. And don’t get lazy about weeding because onions don’t like competition for nutrients.
How do you know when it's time to harvest onions?
When the tops start to fall over, your onion is mature. Gently use a garden fork or hand spade to dig up your bulb, pulling out the whole plant. Lay it out on the garden to "cure" for four to five days in the sun (or under shelter if you're expecting rain) with the tops still attached. To prevent your onions from getting sunburned, lay the tops of one row over the bulbs of another row. Once you can rub your thumb and forefinger over the neck section of the bulb and you don't feel any more moisture, cut off the leaves. Letting the bulb dry completely makes it less vulnerable to decay.
Can I grow onions in a container?
You can! Make sure your containers have at least 10 inches of soil depth. Each onion needs about three inches of space to grow. So, a five-gallon bucket can accommodate about six to eight onions. Make sure the container has drainage holes so it doesn't get too soggy. During the growing season, pull out every other plant to enjoy as green onions. The remaining bulbs will have enough room to make four-inch bulbs as the season progresses.
"Make sure you purchase the right variety for your part of the country," says grower Bruce Frasier, The Onion Man at . "If you plant the wrong kind, you won't have sufficient daylight to produce a bulb and will end up with a great big green onion instead."