How to Plant, Grow & Harvest Onions in Your Vegetable Garden

Onions are one of the most popular vegetables to grow in the home garden. And we totally understand why – onions are easy to grow, don’t require lots of space, they have a short growing season and a variety of uses.

These versatile vegetables are featured in almost every recipe, both raw and cooked. They are incredibly healthy as they are packed with flavonoids and tannins. In fact, their total polyphenol content is higher than in most of other veggies, including garlic, leeks, tomatoes and peppers. The flavonoids are most concentrated in the outer layers of the flesh so make sure you don’t remove too much of them. What is great about onions is that they do not loose the much needed quercetin even when they are simmered. So feel free to use them in making soups, just make sure you slow-cook them. And quercetin is one of the most important flavonoids that gives us protection from oxidative stress. Having onions as a part of your every day diet helps in lowering your risk of some types of cancer like colorectal, laryngeal, and ovarian cancer. In order to get as much nutrients as possible, do not cook your onions more than 7 minutes. 

The best way to ensure you are eating healthy onions that haven’t been too much treated is to grow them your self. As we said, growing onions is very simple. You can choose to grow them from seeds or from sets, but we recommend using sets as they are the easiest and quickest way to grow onions. Onions are a cold-season crop which makes them even more easy to grow because of their hardiness.

We are confident that by now you have decided that onions are a must have veggie in your garden, so all you need to do in order to start growing them is to learn how to plant them, take care of them and how to harvest them. Luckily, we have you covered. Here is our ultimate guide on how to grow onions on the home vegetable garden…

Types of Onions You Can Grow

There are many onion types to choose from. Onions come in three different colors – white, purple and yellow. Each of them has different taste so you should try them and see which ones you prefer. The white onions taste a bit tangy and sharp, while yellow have a much sweeter flavor. Purple onions are best for consuming uncooked. If you are like the majority gardeners and are looking for a sweet onion variety then try Texas Sweet (at southern latitudes) or Walla Walla (at northern latitudes).Generally, onions are categorized into two growing types –  long-day and short-day. Long day onions sprout in late spring or summer when the days between 14 to 16 hours in length, while short-day sprout in late autumn or winter days are between 10 to 12 hours in length.

Choosing Location and Soil Preparation

Before planting your onions, you should choose the right location and prepare the soil. Onions need lots of sun and a very good drainage. Avoid a location that is shaded by larger trees. Have in mind that onions can grow quite large if they have enough room. Onions can grow successfully in a raised bed, so if you don’t have enough space consider building a separate raised bed for them. The soil will also need preparation before you plant your onions. In fact, you should start preparing the soil months before the actual planting. This includes tilling the soil and adding in manure in the fall, mixing in some potting soil if necessary (if your soil is rocky, sandy or with clay) as well as adding compounds in order to get a pH that falls between 6 to 6.8. Make sure you remove any weeds before planting. Also, mix in some nitrogen fertilizer at planting time.

Planting Your Onions

Start onion seeds 6 indoors before transplanting them. Make sure you use fresh seeds. Late March or early April is the best time for planting your onions outside. Make sure the temperatures don’t go bellow 20 degrees F.  Space onion sets or transplants 4-6 inches apart. Set them 1 inch deep, so that their roots are well covered with soil but the top of the plant’s neck is not buried too deeply. This is very important because if too much of the bulb is buried, the growth of the onions will be reduced. Have in mind that once they begin to grow, you can transplant your onions and space them further apart. By doing so, you will increase their growth size. After planting the onions, tamp the soil over the top of them as  they grow better in firm, rather than loose soil. The planting process should be finished by adding some water. You should also add a starter solution of liquid fertilizer after planting.

Caring For Your Onions 

The basic thing your onions need is a steady water supply. Onions have shallow roots so they are not very efficient at taking up moisture. This is why you should keep the soil moist at least until the bulbs enlarge. It is a good thing that onions will recover from drought and start growing once you start watering them again. Give your onions about 1 inch of water per week. If you want them to taste sweeter, give them more water.

It is a good idea to add mulch between each plant right after planting in order to lock in moisture and block out weeds. As for food, onions need supplement with a nitrogen fertilizer once a month.

Another thing to take care of when growing onions are weeds. Onions have delicate roots so weeds can easily damage them, especially if you try to tug them or pull them out. The best way to handle weeds is to cut off their tops with a hoe. 

If you notice that some of your onions have flowered, pull them out instantly as they have bolted and will stop growing. 

Handling Diseases and Pests 

The most common and trickiest pests when onions are in questions are onion thrips. They are black and very tiny pests that suck sap from the onion leaves once they start to expand. Thrips are hard to notice because they hide in the folds of the leaves so in order to check if your onions have them, take a dark piece of paper into the garden and knock the onion tops against it. If there are any thrips, you will notice their bodies on the paper. In order to get rid of them, use an insecticidal soap as recommended on the packaging.

Your onions might also get attacked by maggots, which like to lay their eggs at the base of the plants. In order to fight maggots, cover your emerging onion crop with a fine mesh netting and seal it by mounding soil around the edges.

Aphids can also be a problem when growing onions, as well as diseases like smut, downy mildew, pink or neck rot etc. These diseases are usually a result of a fungi in the soil which can be avoided by rotating crops and providing a good drainage.

Harvesting Your Onions

Onions can be used as spring onions or as scallions. There is no such thing as the perfect size for harvesting – it is all up to personal taste. If you prefer spring onions, you should harvest them just a few weeks after planting. If you choose to harvest your onions when they are fully ripe, then you should wait until the bulbs are big and the tops begin to turn yellow and fall over. When they turn golden yellow, just bend the tops so that they lay flat on the ground. By doing this, nutrients will continue developing in the bulb rather than growing the shoots. Wait for 24 hours. You will notice the tops have turned brown which means they are ready for pulling out! Pull them up, shake off the soil, and trim off the shoots at 1 inch above the bulb and the roots. Leave them in the sun for a day or two then move them to a warm, airy location for 2-4 weeks. This will allow them to slowly dry, which helps to seal the top of the bulb, making the onions less likely to rot.

After a week or so, the onions are ready for storing. Before storing them make sure you clip off the tops of the onions and the roots and remove all the dirt without taking any of the onions’ skin off. Store your onions in a cool place. Have in mind that the sweeter onions go bad earliest, so eat them first. 

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