How to grow onions in containers
Photo by H. Zell
Intro: The savory onion bulb is a popular vegetable for urban kitchen gardens. The onion plant thrives in the cooler months. Onions can be grown year-round, and some onion varieties are better for different seasons. Choose short day length varieties (about 10 hours of daylight), such as Onion Toughball, Troy or Radar variety for fall plantings. Choose long day length (roughly 15 daylight hours) varieties, Marco, Red Baron or Hyred, to plant in the container garden in the spring. White Lisbon is a good variety for the winter. There are many onion plant varieties – choose a variety that will do well in your area and one you would enjoy eating from the garden. Out of the yellow, white and red onions, yellow has the strongest onion flavor, and red is the sweetest.
Scientific Name: Allium cepa
Plant Type: Biennial plant (often grown as an annual)
Light: Full sun
Zone: Zones 5 to 9
Fertilizer: Before planting your onions, fertilize the potting soil. Then fertilize every two to three weeks with a low-nitrogen all-purpose fertilizer. Too much fertilizer will burn the roots and make the leaves droopy or yellow. Do not provide too much nitrogen, as it will delay maturity.
Pests and Diseases: Onion plants can be affected by fungus, blight, rust, rot, onion fly and several other garden pests.
Propagation: The easiest way to propagate onion plants is from sets (small, immature bulbs that were grown from seed and then dug up). Sets also will produce smaller onions, which are better for growing in plant containers. To grow sets, densely plant seeds so as to stunt bulb growth. These small bulbs can be dug up, stored and then planted in the next gardening season. Growing from seeds takes much longer, but these onions will be larger and easier to cut. While some sources say you cannot grow onions from sprouted onions you buy at the grocery store, this is certainly not the case – it is possible. Onion plants take quite a while to mature to the point where they are ready to be harvested for culinary purposes. They will take five to six months to mature.
Misc. Info: Onion plants do best with potting soil that is a bit alkaline, so if your soil is acidic, add a bit of lime. And because they produce bulbs underground, plant them in a large plant container (more than 1 foot deep) so the bulbs have room to grow.
Harvest your onion plants once the leaves have fallen and dried out. In the morning, pull up the onions and leave them outside to dry for the rest of the day (don’t leave them out if it rains or if they are getting burned by the sun). Then let the onion bulbs dry for two weeks indoors. Store them in a cool, dry place hanging in a stocking until you use them. Fresh onion will have the best taste, but they can last for a year if stored correctly.
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