Have you struggled growing onions in the South? Wondering if there was a trick on how to grow onions in the southeast? You’re not alone! We grew our fair share of sad little bulbs for a couple years before we figured out what the onions wanted from us.
Short day vs. Long day
One of the biggest factors to keep in mind is your latitude. Different latitudes have differing amounts of sunlight at different times of year. Short-day onions need 10-12 hours of sunlight to cue the bulbing process, while long day onions need 14-16 hours of sunlight. So…how does this translate into your garden?
In the north it is too cold to plant in the fall to overwinter onions, and by the time the ground is workable in the spring, the day length is already longer than 10 hours. So if you planted a short-day onion, the plant wouldn’t have enough time to grow foliage before the sunlight amount triggers the bulb growth resulting in a sad, small bulb. Long-day onion varieties buy northern growers time to grow onions during their shorter growing season.
Leaves turn into layers
Why does daylight matter so much? For every leaf grown, you end up with another onion layer. The average onion has about 13 layers, so you need enough time to allow the onions to grow those leaves before the sunlight triggers the plant to focus on bulb formation. In the South, with our milder winters, the best time to do that is in the late fall as the daylight is decreasing.
So it is very important to pick an onion variety that is suited for your region.If you’re in the 25-35 degree latitude like us, you’ll want to be sure to get a short-day onion variety. If you live closer to the 40-degree latitude mark you can also experiment with “intermediate day” onions that like the 12-14 hour sunlight range for bulbing.
Sets, Seed or Transplant?
While growing from sets is popular, it is typically the more expensive option and also tends to result in smaller bulbs. Between the other two options–transplanting and direct sowing–the one that is best for you will depend on your area’s specific climate. For example, in our home state of South Carolina, the central and coastal regions direct sow seed in the fall, while for the piedmont area transplanting is recommended. Check out your county extension office’s website to see what is recommended for your region.
Planting and Spacing
Onions don’t like to be planted too deep. Usually no more than an inch under the soil. They like their “shoulders” just at the top of the dirt. If you plant them too deep, they will struggle to bulb up. Also, don’t overcrowd them if you want larger onion bulbs. They may look tiny at planting time, but give them 6-8 inches of space to allow them room to grow outwards later.
Nutrition
Onions are heavy feeders, which means they like lots of nitrogen. So before planting, be sure to mix in some compost high in nitrogen, like a manure-based compost. Also, consider using fish emulsion foliar fertilizer regularly to help the plants produce nice, large bulbs. Nitrogen helps plants grow foliage, and remember, every leaf is a new onion layer later. Stop fertilizing when you notice the bulbs beginning to form. Too much nitrogen at this stage will hinder the bulbing process. You know what else loves nitrogen? Weeds! While weed-pressure decreases as we go into winter, be sure to keep the onion beds weeded regularly in the late fall and early spring.
Where to plant them?
Even if you are short on gardening space, onions can fit into your veggie plot with ease. Since they are planted in the fall and overwinter, they will be planted as the summer crops fade and harvested before the next summer garden is in full swing. Because of this, we love interplanting them with other crops. Not only does it save space, but plants in the allium family are a great pest deterrent.
Harvest
Onions kindly will flop over when the time comes to harvest them indicating that they are ready to harvest. When you see about three quarters of the tops fall over in your garden, it’s time to pull them up and lay them out to dry in a breezy, but shady spot. Once the foliage has dried up and there is a nice papery skin on the onions, it’s time to trim off the roots and snip off the tops about an inch or so above the bulb. Store them in a cool, dark and dry location. Generally speaking, short-day onions do not store as well as long-day varieties. But if you keep them in ideal conditions (between 45F and 55F and 50-60% humidity) they can last several months.
Found the how to grow onions in the southeast post helpful? Check out more fall gardening tips here.
Recommended Cultivars
Our regional extension office recommends the following onion varieties for the southeast: