CorabethGodsey said:
I am admittedly jealous. I don't even start onions inside for another two weeks. Last year was my first year planting onions, from starts I bought at the store. This year I am jumping in the pool completely, starting red onion and yellow onion, plus the green onion and leeks from seed. Last year the leeks looked amazing, but the yellow onions had almost no size, most being golf ball or plum size.
I live on a slope. More water? Hard to overwater on a slope in a drought. Any fertilizing, planting tips and hints to get bigger onions?
Varieties: Globe and Flat of Italy.
When I hear that onions do not form large bulbs, I generally think of three possible causes.
First, the onion seeds/plants need to be started soon enough so that they have enough growing time before bulbing. Ideally you want the plants to be about the size of a pencil when you plant outside about 4-6 weeks before last freeze. For Sioux Falls SD, you are shooting to plant outside in mid April. I'd think the sooner you get your seeds or sets started, the better chance they have of getting to pencil size by then.
Second, onions are photoperiodic, meaning the length of daylight hours in the day on June 21 influences when the plants bulb up. For Sioux Falls, because of your long hours of daylight, you need to be growing long-day onions. It looks like most of the globe onions are long-day, so that works, but the Flat of Italy is intermediate day, so those will start to bulb up too quickly and will mature before they reach maximum size. Don't count on the stores to sell the right onions for your region. The stores here in Georgia are selling long-day onions to unsuspecting buyers, and the long day onions will never bulb up with our shorter days.
Third, if the onion transplant is buried too deeply, it will not bulb up properly. The onion is actually the bottom part of the stem on the plant, and the onions grow above the ground, not in the dirt. When I plant my onions, I put the plant in the ground only about an inch, or less. I have to go back daily for a week after planting to keep setting some of the plants upright, but eventually the roots grab and they stay upright. Here is a photo of the onions nearly harvest; you can see the bulbs above the ground.
Beyond these three ideas, water and fertilizer is also helpful to growing onions. Dixondale Farms has lots of great info on their website about how to grow onions; I definitely recommend taking a look at that.
