Bulb onions (Allium cepa) are easy to grow and are a great crop to plant in the vegetable garden. These are the common round onions we know from the grocery store as opposed to non-bulb onions like scallions or leeks. Scallions, ‘bunching onions’, or ‘green onions’ are those long thin onions that do not form big bulbs at the root.  And leeks grow tall with big flat green leaves and an elongated white stem that is the prime part for use in cooking.  There are a number of other onion plants you can also grow that form small bulbs or even stay tiny and form clusters like chives.  Onions are tasty and healthy foods that do not take up a lot of space in the vegetable garden.  All kinds grow well in the Southern California area if they are given reasonably rich soil and plenty of water.  Here are some tips on how to plant onions in the vegetable garden.

Onions are usually planted in the spring or autumn. They are commonly started by one of three methods: seed, seedlings or sets (for bulb onions).  You can actually plant them during the winter in any of these forms, too, if you live in a mild winter climate.

Seeds of bulb-forming onions do best in an area with a long summer like ours because they have time to form good-sized globes. This is the most inexpensive way to plant them. Seed them in rows and thin them to about one plant for each 4″. Unlike some other parts of the country, we don’t have a problem with the onion fly here.  You can choose from many different varieties of reds, yellows and whites.  The standard yellow varieties will produce onions with the longest storage capabilities.

Seeds are also easy to grow for other types of onions.  Leeks (Allium ampeloprasum var. porrum) are best started in a small area where the seedlings can all reach 4 – 8” tall before being transplanted.  The best way to transplant leeks is to trim the roots of the seedlings and drop each plant in a 6 – 8” hole made by a dibbler or other stick-like tool.  Do not fill in the hole with soil, but do water the young plants in.  The hole will help blanch the stems as the leek seedlings grow bigger and fill in the space.

If you buy young plants of any kind of onion to transplant from pots or 6-packs or you start your seeds indoors, planting instructions are pretty much guided by the same rules as seeding directly in the ground. Plant them about 4 – 6″ apart in rows. Leeks can also be grown at the same spacing, but they will be easier to dig when ready if you leave a little more space between plants or larger spaces between rows so you have more room to insert the shovel.  For all onions transplants other than the leek, plant just the rooted base, leaving the long thin grass-like tops free of soil.  In Southern California, autumn is the best time to plant seeds since you want them to be strong enough to over-winter and have a long season to grow. Spring is the best time for transplants.  But you can also plant either at any time of the year, though the cooler seasons are better than in the heat, especially in the hot, inland areas.

Planting from sets is probably the most universally easy and safe way to grow dry bulb onions. You can buy the little bulbs (that were grown from seed already) from garden centers in autumn, winter and spring. These, too, should be spaced in rows at 4″ – 6″ intervals. Just press the very bottom of the bulb into the soil: don’t bury it.  You may have to replant some little onions occasionally as they can get dislodged by birds.

Plant your bulb onions, leeks and scallions in rich soil and full sun and make sure they get regular water. Onions are easily grown and a great staple of the home vegetable garden. I like to inter-plant my bulb-forming onions with lettuce since the lettuce will be cropped by the time the weather starts to warm and the bulbs begin to swell. This way I get more growing out of a limited space.  Scallions make nice border plants in the vegetable garden.  If you don’t harvest all your scallions or green onions, the remaining plants will form clumps and can be grown on from one year to the next. 

Although I haven’t seen it mentioned elsewhere, leeks that go to seed (flower) or bolt before you can crop them are also best left in the ground.  The flower shoot that grows up inside the long stem will ruin the leek texture so I’d advise not cropping the plant at all.  If you let the blooming leek remain and die back in the summer, you will get one or more plants sprouting for next year.  The second year’s leeks will likely be a bit thinner, but will still be great for cropping and eating – so long as you harvest them before they start flower spike formation.

You may also want to plant chives.  The regular chive has a pretty pink flower and makes a decorative, low profile plant.  The garlic chive has a flat leaf and taller panicles of white flowers that are very decorative in the garden.  Both types of onion chive offer leaves to be snipped for salads or cooking during most of the year except the in middle of the winter when clumps of the miniature bulbs die back into dormancy.

These are the most common kinds of onion to grow in the garden.  They are heavy feeders and like lots of organics dug into the soil and regular feeding.  Give them full sun and they will grow easily with little likelihood of pest damage.  You can also try some other members of the onion family like Egyptian or Walking Onions, pearl onions, Italian round onions, shallots and garlic.  All are easy, tasty, nourishing and fun to grow!