Most Dixondale Farms customers strive to grow the largest onions possible. Providing your plants with enough space to bulb is crucial starting from the day you plant your onions. We recommend planting your onions no more than 1/2 to 1 inch deep and 4 inches apart. These dimensions work well for all varieties of onions. Don’t worry that the bulbs are planted too far part; the foliage will shade the bulbs and prevent sunscald.

large onion bulbs

When Onions Start to Bulb

Onions will start bulbing once they’re receiving enough sunlight. Bulbing is dependent on daylength and temperature, not the size or age of the plant, so choosing the proper varieties for your area is critical. Short day onions require 10-12 hours of daylight, intermediate day varieties require 12-14 hours of daylight, and long day varieties require 14-16 hours. This is why long day varieties do poorly in the south and short day varieties aren’t as effective in the north; they produce plenty of tops, but no bulbs. They do mature more quickly, but they produce smaller bulbs. Check out our daylength map for more information.

Once bulbing begins, the ground will start cracking around the bulb as the expanding bulb starts shoving the dirt out of the way. About two-thirds of the onion bulb should be above the surface as it matures. See picture on right. 

When to Stop Fertilizing

Be sure to stop fertilizing after your onions start to bulb to discourage further leaf growth and allow the bulbs to mature properly. Continuing to fertilize keeps the tops growing taller and prohibits the onion from allocatings its energy towards the bulbing process.

Don’t Plant Too Deep!      

If you’ve planted the onions too deep, you may not be able to tell when the bulbing process begins as the onion is too deep in the ground. You’ll end up with smaller bulbs shaped similar to torpedos because the soil will restrict the plants from bulbing properly. 

We want our customers’ crops to reach their full size potential. We are available year around to answer any growing questions you may have along the way. Contact us by phone at (830) 876-2430 or email at