Onions are easy to succeed with in the right soil. Not a crop for growing hydroponically, though you could grow a few at a time indoors under full sun grow lights. The most efficient way is growing them outdoors. They don’t need tons of space per plant, and they are very shallow rooted, which makes them media economical.
You can grow a good number of them in a rather small space. If you choose the right type of onions to grow, you can have a good supply of quality onions that will store very well for months in a cool, dry place that gets no natural light.
There are three ways to grow onions; from seed, from sets, and from plants. Most people grow onion sets in their outdoor garden, because seed takes more than one season to deliver a harvest. You will only find onion seed available from seed companies that supply market farmers. Surprisingly, onions grown from seed or plants are far superior to those grown from sets. Sets are just baby onions that are harvested at a very tiny growth stage and dried to prevent rot. As you can imagine, this would definitely deplete some vigor that the plant would put into creating a quality product in the end. It also makes your plants highly prone to disease. Yet, if all you know is to grow onions from sets, obviously that’s what you do.
Sown outdoors, onion seed is planted in the fall for the next year’s harvest. Hence the sets – they make growing onions more convenient. You can start onion seed indoors in February or March, and transplant them when the weather is right for outdoor planting in your area. Seed and sets are both very inexpensive ways to get this crop started. Plants will naturally be more expensive, but allows you to plant and harvest with the rest of your backyard garden crops.
Onions need excellent drainage and about an inch of water total a week from rain or your hose. They must be grown in full sun, and being very shallow rooted, be sure to keep their growing space weeded, or the weeds will crowd them out and rob their food resources. Be sure no water pools from rain where you plant them. Never plant seed or plant onions with set types as any diseases will spread rapidly. The best harvests will come from humus-rich sands, light loam, or other soil types with high humus content. This means that they will also do well in good quality potting mixes, making them great candidates for large containers without the need for lots of depth.
How many onions can you grow in a container? The dimensions of the surface play a big part in that. In the garden, you plant onions in rows 18″ apart and the spacing depends on how big the onion bulbs will get at maturity. The recommended average spacing is 6″ on center (3″ apart), so you won’t want new plants any closer to the container wall than 3″. A wall-mounted pallet garden should give you about 18 feet of row space, which should accommodate 5 onions per section, giving you a harvest of 50 mature bulbs. So, even someone living in an apartment can grow their own organic onions with a full-sun spot for a pallet garden.
What about a Rubbermaid tub, Earthbox, or raised planter? The shallow utility tote tub will save on excessive fill over the Roughneck type at only 5″ deep. It gives you 20″x15″ of surface area, which will give you 3 rows at 14″ long -translating into about 12 onions total. You might get 3-4 more in an Earthbox, which measures 29″x13.5″. The utility tote is better, because you’re loosing too much width on the Earthbox for rows that have a little breathing room. You can make raised planters in many sizes, so your available ground or balcony space is the deciding factor. There is also the possibility of lining your railings with planters one usually grows flowers in. These are wide enough for a single row, and if you’ve got 20 feet of railing, you can grow at least as many as in a pallet garden. Just make sure you’ve given these options good drainage.
Where you live will determine what kind of onions you can grow. There are long-day and short-day varieties. If you live in the North, you want long-day onions, and in the South, you need short-day types. Look for varieties that are known for good long storage traits.
How long will 50 onions last you? Consider how many you’ve bought and used in the past 4-6 months. And then calculate the cost of purchasing mature onions versus the cost of onion seed. Add the benefit of knowing exactly what went into growing your onions, as opposed to buying them at the store.
Image if mixed onions courtesy of Wikipedia.