Growing Onions - My 4 Favorite Crops and 3 Growing Methods for Sowing and Planting Onions

Onions are one of the most versatile vegetables in the kitchen. They come in different varieties, such as yellow, red, and white onions. In addition, the shallot, as a related species, belongs to the allium family; shallots are often grown for their aromatic and mild flavor.

Onions are perhaps the most versatile vegetable you can grow yourself in your vegetable garden. The great advantage of growing onions is that you can use them almost all year round in the kitchen: raw in a salad, stewed in a casserole, or as a flavoring in soups and sauces. In addition, onions are also very healthy. They are low in calories but packed with vitamins B and C, and important minerals. By growing your own onions, you know exactly what you are eating and you can enjoy fresh, flavorful onions from your own garden.

There are different types of onions, such as pearl onions, large yellow onions, and red onions, and there is great variety in breeds and usage possibilities. From mild to pungent, small pearl onions to large storage onions. Vegetable gardeners have three options for growing onions: using onion sets, pre-sown onions, and direct sowing in open ground. I even grow them in all three ways because… you can never have enough onions.

A good start begins with the right location and soil. Onions love a warm, sunny spot where they get plenty of sunlight. They need at least 5 to 6 hours of sunlight per day to grow well. The soil should be loose and rich in humus so that the roots can develop properly. Make sure the soil stays well-moistened, but avoid it becoming too wet, as that can lead to rot. Drying out is just as fatal: soil that is too dry prevents the onions from growing properly.

Also consider the companions of your onions: preferably plant them next to root vegetables like carrots or parsnips.

By choosing the right location and considering companions, you give your onions the best chance for healthy growth.

During cold periods, you can provide extra protection to your onions by keeping them warm with straw or fleece, so they are not damaged by frost.

Anyone who wants to grow beautiful, healthy onions year after year should practice crop rotation. By not planting onions in the same spot every year, but alternating them with other root crops such as carrots or parsnips, you significantly reduce the chance of infestation by nematodes and fungi. Nematodes can attack the roots of onions, causing growth to stagnate and harvest to be disappointing. By ensuring good rotation in your vegetable garden, you give diseases and pests less of a chance to build up in the soil.

In May, you can give your onions an extra boost by adding a potassium-rich fertilizer. Potassium stimulates bulb formation and ensures your onions become firm and healthy. Be careful not to use too much fertilizer, as an excess can cause problems. By following these care tips and paying close attention to crop rotation, location, and moisture, you can enjoy healthy and sustainable onion cultivation in your own garden year after year.

Before you grow onions, you have to think about when you want which onions. In the spring, for example, we eat many more salads than soup. So, spring onions will be more interesting here than large storage onions, which can add flavor to a large pot of soup with their strong taste. Before I talk about the ways you can grow onions, I will go through the 4 onion crops I want chronologically throughout the year:

• Sowing onions: This is a traditional method where you sow onion seeds directly into the ground. With sowing, it usually takes two years before you can harvest an onion.
• Planting onion sets: Planting onion sets is a simple and fast method for growing large onions because you put small bulbs directly into the ground and they quickly grow into fully grown onions. Onion sets can be harvested in the same year, while sowing requires a year of patience.
• Winter onions: These are planted in the fall and can be harvested early in the spring.
• Spring onion: Specifically grown for the young, green foliage used in salads.

Early spring onions for salads, garnish for soups, for the first peas, and to flavor all my dishes. From May on, we use those spring onions every day. February 10: I sow 6 to 8 spring onion seeds in a tray with 4 to 4.5 cm cells, which I keep indoors under grow lights. I transplant the modules into my tunnel at the end of March. I want spring onions quickly, so I force them indoors with grow lights. You could also do the same perfectly well in a greenhouse, but then it takes a little longer.

March 30, I start my crop with summer onion sets. Because I can use spring onions early in the kitchen, I take my time for my ‘summer onion sets’ crop. Without those spring onions, I would also let the sets root in trays to save some time. Given that I have spring onions under foil or glass and I also have ‘winter sets’ in my greenhouse (which will be removed for the peppers and paprika’s at the end of May), I take all the time I need for this crop. I plant them at the end of March, beginning of April, and immediately apply insect netting; the coarsest netting of 90 grams/m² is ideal. At the end of May, I add some extra potash; potassium provides extra-large, healthy, and flavorful bulbs. The summer onions are usually ready to be harvested around mid-July, when the foliage starts to hang and turn yellow. After harvesting, onions usually need to dry for a few days to weeks before they are suitable for storage. These will keep until February or March if you store them correctly.

March 30: When I plant my sets, I also go to sow my sowing onions in open ground. I use a cultivator to loosen my soil to about 15 cm deep, sprinkle a handful of organic fertilizer pellets and a handful of potash, and use a garden hoe to make a furrow a few cm deep. I fill this halfway with sowing and cutting soil (I use coconut soil for this, nicely fine). I sow a row of onion seeds and cover them back up with a cm of sowing and cutting soil. That coconut soil provides good, airy, moisture-retentive soil to germinate in. Once germinated, I apply insect netting.

Here you can see a video on how I grow my summer sowing onions

October 20: Winter onion sets under glass are ideal if you want to enjoy fresh onions from your own garden early in the spring. By planting these onions in the fall in a warm, light spot – for example, in a greenhouse or cold frame – you give them a head start. Make sure the soil remains well-moistened, but not too wet, to prevent rotting. In the second year, a flower stalk may appear on winter onions; this is a sign that the onion is ready to bloom and form seeds. In May, when the chance of frost has passed, you can transplant the onions into the open ground. There, they will continue to grow into firm, flavorful onions that you can harvest early in the season. This gives you a nice head start on the rest of the onion season and allows you to enjoy your own harvest for longer.

Onion sets are small onions that are grown from seed and then put into a dormant stage at an early stage by cooling. As soon as we plant the small plants out in the vegetable garden, they continue their growth process.

Plant them with the tip just above the ground, about 10–15 cm apart depending on the size of the mature onions. You can also plant them at half the distance and harvest half of them at an early stage as spring onions. Leave 30 cm between the rows. Planting onion sets is the easiest way to grow a large number of onions that store very well.

A disadvantage of this cultivation method is the more limited number of varieties. Onion seeds come in many, many varieties, colors, sizes, and weights. But for the average strong onion for soup, stews, and other daily kitchen dishes, I grow from onion sets.

You can pre-sow bunches of seed onions yourself in trays with holes 4 to 4.5 cm in diameter. You'll need quite a few grow lights at home because onions won't grow without sufficient light. Start indoors in late February or early March and sow 4 seeds about 1.5 cm apart in each module so you can easily separate them for planting out. I use potting soil for vegetable gardens for the bottom half of the tray and seedling/cutting soil for the top half. I keep them well-moistened in my propagator, but also on a warm windowsill with cellophane over your trays or pots to prevent them from drying out—the seeds germinate well this way. Once sprouted, you need to place the onions in a cooler spot (15°C is fine) and they must have maximum light. You might have a south-facing windowsill and be lucky enough to have it be sunny. I use grow lights, which shine whenever I want them to.

This Ailsa Craig can weigh up to 1 kilogram. If necessary, I transplant the onions again into a P7 pot. In the first half of April, I transplant the seedlings individually. I loosen the roots of the seedlings, plant them 10 to 15 cm apart, and leave 30 cm between the rows. Your onions will have a nice head start compared to onion seeds sown directly in the ground around that same period. It is best to loosen the soil to a depth of 15 cm with a cultivator. At that time, also work in some compost, a handful of universal fertilizer granules, and a handful of Garden Potash (Tuinkali) per m2 into the soil. Water well at the beginning and keep the plants weed-free. 4 weeks before the expected harvest date, you can sprinkle another handful of Garden Potash around the plants for thick, tasty onions. This technique is actually the same for bunching onions, with the difference that I sow 6 to 8 seeds centrally in the tray and then transplant the plugs later in one clump. I do not separate them as described above.

For large onions to store, the easiest way is to grow them from sets, but it can also be done by direct sowing. Usually, we sow bunching onions in rows to thin them out to 5 to 10 cm, with 30-40 cm between the rows. In mid-April, I work my soil to a depth of 15 cm and incorporate some compost, a handful of universal fertilizer granules, and a handful of Garden Potash per m² into the soil. With a garden hoe, I make a groove a few centimeters deep every 30 to 40 cm. I fill the groove with coconut fiber soil up to 1 cm from the edge; you can also use sowing and potting soil or a peat-based mix. I sow my onion seeds on the coconut soil and fill the groove completely with an extra centimeter of coconut soil. Use fresh onion seeds, as they lose their germination capacity quite quickly. After germination, it is best to install insect netting to protect your crops against the onion fly, which wants to lay its eggs at the base of your onions. White larvae emerge from those eggs, and what they want is the same as what you want... eating your onions. Thin your young seedlings to 10 to 20 cm. It goes without saying that an Ailsa Craig that can weigh up to a kilo is thinned to a distance of 20 cm, while a silver-skin onion is thinned to 5 cm. You have to follow the logic of the variety you choose here. And then, 4 weeks before the expected harvest, you give your onion plants another handful of Potash; at that stage, the onions grow thicker, and potassium helps with this significantly.

On our YouTube channel: @plukkers_com you will find a growing video from 2017, "Growing Onions from Sowing to Harvesting."

There you go, this is almost everything I know about growing onions. Hopefully, you will also choose a cultivation method and an associated growing technique and grow your own onions. If you want to support this site, you might consider purchasing your vegetable garden supplies in our webshop.

Tom