How Long Do Onions Take to Grow? The shape, size, flavour, and colour of onions vary. The duration to maturity varies depending on the type of onion and whether you grow plants from seed, transplants, or sets. When planting onions, taking these factors into account before planting can help you better determine when your onion crop will be ready for harvest.
How Long Do Onions Take to Grow?
1. Starting Onion Seeds
Starting onion plants from seed takes the longest for onions to mature, but onion seeds provide the most variation. Plants can mature enough to harvest after up to five months of the growth period. Allow the soil temperature to raise to at least 50 degrees Fahrenheit before sowing onion plants from seed.
Short-day onion types can be planted four weeks before the first frost in locations with moderate winters. Because direct sowing in the garden may not allow long-season onion types to mature, starting from seed is better for short-season kinds and scallions.
Seeds can also be planted in pots, flats, or trays, according to Harvest to Table. When the seedlings reach 4 inches in height, thin them to 1 inch apart. Sow them two weeks before the final average frost date in spring, as long as the soil temperature has reached 50 degrees, or four weeks before the first average frost date in October. Sow them half an inch deep and one inch apart in the garden.
2. Onions From Transplants Take to Grow
To reduce the time between planting and harvesting, start the onion seeds indoors eight to twelve weeks before the last frost date in your location, according to Cornell University. Plant seedlings outside when they reach 1/4 inch in diameter, which should be two to four weeks before the latest frost date in your location. Harden off onion seedlings gradually before transplanting them outside.
Check that the soil temperature has reached at least 40 degrees and the air temperature has reached at least 45 degrees. It takes roughly two months for transplants to attain full maturity. Onion transplants look like miniature scallions. Scallions should be spaced 1 inch apart.
Soak these transplants in compost tea for 15 minutes before planting, plant them 1 to 2 inches deep, and place them 4 inches apart if you want them to grow into larger onion bulbs. According to UC Davis Extension, if you want larger bulbs when you harvest them, aim for larger bulbs when purchasing your transplants.
3. Growing Onion Sets
Cornell recommends planting onion sets, which are miniature, dormant plants cultivated the previous year, for the quickest harvest. In about 2 months, these sets will be fully ripe and ready for harvest. Sets are also less vulnerable to illness, but growing from them limits your onion variety options. Smaller sets give the best results, therefore choose sets no larger than 1/2 inch in diameter for the best outcomes.
4. Green and Pearl Onions
Green onions or scallions can be harvested in as little as 20 to 30 days. The fragile, green tops of these onions are picked before the bulbs fully form. Pearl onions, also known as pickling onions, are picked when the bulbs are approximately 1 to 2 inches in diameter, 60 to 90 days after planting. These onions have a sweeter flavour than larger onions. In Mediterranean climates, these onions grow nicely from late winter to early spring.