Does it take two years to grow onions?
Answer: All onions and leeks are biennial, meaning that they normally take two years to grow from seed, flower and set seed again. First, they grow “vegetatively,” forming roots, leaves and other plant growth.
Onions may be grown from seed, rather than sets or plants, but will take 3 to 4 months to mature. Green onions grown from sets will be ready to harvest in approximately 6 weeks. If you want large onions for cooking, plant the bulbs 10”-12” apart and just under the surface.
While onions are easy to grow, they can at times be affected by pests. In the home garden setting, diseases are seldom a problem. However, good cultural practices can help prevent plant diseases. Plant onions in different parts of the garden each year, a practice called crop rotation.
Onions mature in 95 to 115 days for bulbing onions depending on the variety, and about 60 to 70 days for green onions. Onions are best planted in late winter or early spring for summer through autumn harvest. Green onions or scallions can be harvested about 2 months after seed sowing.
Onions are only harvested certain months of the year, but society uses onions all year long. The only way to keep supplying the onions year-round is to store them. You've probably been using storage onions your whole life and simply never realized it.
You can start sets inside, as well: "If you don't have the outdoor space available for gardening, you can actually grow onions indoors year round in containers," she says. "Just make sure they are being grown in an open and sunny area in your home with fertile soil and good drainage."
Onions are cool-season crops that require 90 days or more to reach maturity. Because of this long growing season requirement and their preference for cooler weather, planting onion seeds directly into the garden in the spring makes it difficult for the bulbs to reach a good size before warm temperatures arrive.
This happens because onions are biennials. They grow foliage and a bulb the first season, then bloom and set seed in their second growing season.
You can still add onions to your patch. While it's smart to stay away from bulb onions in June because there isn't a long enough growing season for them to reach maturity, this is not the case with bunching onions (otherwise known as green onions or scallions).
All onions require full sun for the best growth. Overcast skies and cool temperatures during the growing season will delay bulb formation. Sweet or mild onions are short-day onions.
Can I plant onions anytime?
Here, fall is ideal onion-sowing time in Southern California. Think October through December. Checking my notes from past years, I see that I got decent onion crops from sowing as early as mid-September, and as late as Christmas. But my best onion crops were sown between mid-October and the end of November.
Sets should be planted at a depth of 1 to 1 1/2 inches in rows 12 to 15 inches apart. For dry onions, plant the sets 2 to 3 inches apart. Sets grown for green onions can be planted closer together.
These would include the vegetative phase, the bulbing phase, and the flowering phase. In most cases you'll want to harvest onions prior to any flowering or seed head production, so I often don't mention the flowering phase when talking about growing onions in a home garden.
Optimal soil temperature for germination: 21-25°C (70-75°F). Seeds will emerge in 6-12 days, depending on conditions.
For those who haven't grown onion sets or seeds before one question is often asked - how many onions grow from an onion set or seed? The answer is simple, one onion grows from an onion set or a seed. Many onion sets are "heat-treated" nowadays to stop them bolting into flower.
Ideally, onions should be stored in a cool, dark place between 45 and 55 degrees F. Whole, raw onions will last two to three months when stored in a cool, dry place.
Practice crop rotation with onions. Don't plant them in the same location year after year, as this can encourage the spread of diseases that affect the crop.