For some gardeners onions are one of the easiest things to grow in the backyard garden. For others they can be quite the struggle. We find that many backyard gardeners struggle with onions because they don't quite understand the onion growth cycle and the needs of the plants as they grow. Below we've provided our top 10 onion growing tips to help you grow the best onions you've ever had!
#1 Choose the Right Day-Length Variety
Onions have two distinct growing phases -- the vegetative phase and the bulbing phase. The green foliage is produced in the vegetative phase and the bulb enlarges during the bulbing phase. Bulbing in onions is triggered by day length.
You must plant the right day-length type for your area, whether that be short-day, intermediate-day, or long-day onions. Below is a map to let you know which type is best suited for your climate.
#2 Hybrids Outperform Open-Pollinated Varieties
We've trialed quite a few onion varieties over the years, and the hybrid onion varieties always seem to outperform the older, open-pollinated onion varieties. The hybrids show more vigorous growth and usually produce a larger onion. Of course if you want to save onion seeds, you'll want to stick with an open-pollinated variety. But if your goal is to grow big onions, choose a hybrid variety.
For example, last year we grew Texas Early Grano 502 (an open-pollinated variety) beside Timon (a hybrid variety). Both are round, sweet, short-day onion varieties. The Timon variety significantly outperformed the open-pollinated Texas Early Grano 502, also known as "Texas Legend."
#3 Grow Your Own Onion Plants
There are many benefits to growing your own onion plants. For one, it's cheaper to grow your own plants as opposed to buying them -- especially if you already have a seed-starting setup at your home. Secondly, growing your own plants means you get to pick the varieties you want to grow. If you buy plants, you only get to choose from the varieties that the plant grower has.
Growing your own plants also ensures that the onion transplants never experience the stress of being out the ground for too long. Onion plants that are sitting in a warehouse or hardware store will be somewhat dried and will take longer to start growing when you put them in the ground. But if you go straight from your seed-starting room to the ground, the onion transplants will start growing much faster.
#4 Plant at the Right Time -- Not Too Early, Not Too Late
November is the ideal time for us to transplant onions here in south Georgia. Over the years we've experimented with different planting times. We've tried planting onions in late October and we've also planted onions as late as December.
When we planted onions in late October, it seemed like we had more bolting in the spring and also some onions rotting in the ground before they were ready to harvest. When we planted onions in December, they didn't get quite as large as the onions planted in November. This is likely due to not having enough grow time during the vegetative phase.
#5 Use a Balanced Fertilizer at Transplanting
Onions are heavy feeders and thrive on plenty of nitrogen in the soil. But initially, they will need some phosphorous and potassium to encourage root development on the newly transplanted onion plants. As a result, it's best to give them a balanced fertilizer at transplanting -- something with relatively equal parts of nitrogen, potassium, and phosphorous.
We like to use Nature Safe 8-5-5 or an equivalent balanced organic fertilizer in the furrow at planting. We make a furrow in the garden and then sprinkle the organic fertilizer in the furrow. We'll then place our onion plants in the furrow and cover the fertilizer as we work our way along the row.
#6 Go Heavy on the Nitrogen
As mentioned above, onions are heavy feeders and require lots of nitrogen. Once your onion plants have started adding new green vegetation, you'll want to keep them happy with a nitrogen-based fertilizer. We like to use Nature Safe 13-0-0, but you can also use manure or other nitrogen-based fertilizers.
We'll side dress the onions at least twice during the vegetative phase with the all-nitrogen fertilizer. We basically sprinkle the fertilizer beside the row of onions and then scratch it into the soil with a hand hoe or wheel hoe. Incorporating the fertilizer into the soil will ensure it is more effectively delivered to the plants.
#7 Onions Like Plenty of Water
In addition to liking plenty of nitrogen in the vegetative phase, onions also benefit from ample water. We almost always plant our onions on drip tape irrigation so that we can easily supply water to them on a frequent basis. We'll let the drip tape run for a couple hours at a time when the plants are small. But once the plants get larger, we'll often let the drip irrigation run overnight several times a week.
You don't want the ground to be oversaturated, but you want to make sure that the onion plants are never starving for water. Keep an eye on the vegetation to make sure it's not wilting. Onion plants will usually soak up the water pretty quickly and be hungry again in the next couple days.
#8 Stop Feeding When They Start Bulbing
Onions will start bulbing based on the day-length trigger mentioned above. When this happens, you'll usually start to see the ground cracking around the onion plant as the bulb enlarges. You'll sometimes also see the bulb being exposed above the soil.
You'll want to stop fertilizing at this stage. Once bulbing begins, the onion has already produced all the green vegetation that it will produce. It is now devoting all it's energy to enlarging the bulb. Make sure they have ample water, but don't give them any fertilizer once they start bulbing.
#9 Don't Cut the Onion Tops
There's quite a bit of misinformation online about cutting onion tops to produce a larger onion. We highly recommend not cutting your onion tops if you want to produce large onions. The onion tops are necessary for the plant to generate energy to make a large bulb during the bulbing phase.
You want to maximize the green growth during the vegetative phase so that the onion has lots of green foliage for photosynthesis. If you reduce the amount of green foliage by cutting it, you'll sacrifice your final bulb size. If you're wanting green onion tops to eat, try growing a few spring or bunching onions to use for that.
#10 Keep the Weeds Under Control
Onions take a long time to grow and produce a large bulb. As such, keeping your onion beds clean and weed-free is very important. When onion beds get overgrown with weeds, these weeds tend to rob the onion plants of nutrients. Weedy growth can also create too much moisture around the onion bulbs and cause them to rot when they get close to maturity.
Do your best to keep your onion beds weed-free throughout the growth cycle and you will be rewarded. If you need to use a straw mulch to help with this, go for it. We have found that lightly scuffing the soil with a hand hoe every few weeks is an easy solution.
Enjoy Your Onions!
We hope these onion growing tips help you grow some large, tasty onions in your backyard garden. Onions are relatively easy to grow once you understand the growth cycle of the plant and the needs it has during that growth cycle. Once you get the hang of it, it will be a breeze every single year!