Planting, growing & harvesting onions - a guide

Onion types: onions, spring onions and co.

The onion (Allium cepa) belongs to the amaryllis family (Amaryllidaceae) and the genus Allium, which also includes garlic, leeks, chives and shallots. Botanically speaking, the onion is a perennial herbaceous plant, although it is often cultivated as an annual. There are many different types of onion, which differ mainly in taste, size and use. The best-known types are the green onion, the spring onion and the shallot.

Onions can be used in a variety of ways in the kitchen and in the garden. They are easy to care for and uncomplicated to grow. They are rich in vitamins (especially vitamin C), minerals and fiber and are therefore very healthy. Onions also have antimicrobial properties and contain antioxidant plant substances.

Growing onions - these varieties are available

In the world of onions, you will find a wide range of varieties that differ in shape, color, taste and ripening time. In addition to the distinction between species, there is also a division into summer and winter onions, depending on the growing season. Below you will find an overview of onion types and a few examples of onion varieties.

Old onion varieties

Old onion varieties are particularly tasty and usually more resistant to diseases and pests.

• Cipolla di Tropea: Italian red & sweet variety, for salads and raw consumption
• Borettana: Italian yellow, mild & flat variety, can be used as a pearl onion
• Bedfordshire Champion: English, yellow & spicy onion, good for pickling
• Pear-shaped: Yellow variety from Franconia, elongated onions, quite sweet
  

Onions

Onions are the most commonly cultivated and used variety and are characterized by their round shape and yellow or white skin.

• Stuttgarter Riesen: A yellow, round onion that stores well
• The Kelsae: From England, very mild & large onions
• Zittauer gelbe: Proven, roundish, firm, durable & robust
• Texas Early: A sweet, yellow onion, large in size, late maturing

Spring onions

Spring onions, also known as spring onions, are very tender and are particularly suitable for salads and garnishing. They are thinner and milder in taste than onions and are often used raw or in salads. They are sown in sets as they can only be stored for a few weeks after harvesting.

• Blanca de Lisboa: Popular, widespread, mild variety with a white stem
• Freddy: Extremely hardy, high-yielding
• Spring Performer: High-yielding, with green foliage and long, white stems
• De Vaugirard: Snow-white, lush, flat-round bulbs, fast-growing

Red onions/purple onions

Red or purple onions are sweeter and milder in taste than conventional onions. They are ideal for salads and raw dishes.

• Rossa di Toscana: Traditional round variety from Italy, stores well
• Di Genova: Early ripening, flat-round, large, very mild and tender, does not store well
• Tropea Rossa Lunga: Oval/elongated, very tender, for fresh use
• Braunschweiger Dunkelblutrote: Well-proven variety with firm, flat-round bulbs, stores well

Shallots

Shallots have a smaller, elongated shape than onions and are prized for their delicate, sweet flavor.

• Longor: elongated, yellow-brown shallot with a delicate flavor
• Biztro: tasty aroma; roundish, red-brown
• Hermine: white skin, roundish, very good aroma, can be stored for a long time
• Eschalote Grise: small, gray, spicy shallot with firm flesh

Winter onion/winter-hardy onion varieties

Winter onions are particularly robust, frost-resistant and can also be grown outdoors in colder temperatures. They are planted in the fall and harvested in the spring.

• Senshyu Yellow: Yellow variety
• Freddy: Extremely hardy, high-yielding
• Shakespeare: Robust variety
• Tonda Musona: Round, red, sweetish onion

Sowing or planting onions?

Onions can be sown directly as seeds in the bed or planted as pre-grown onion sets in the bed. Onion sets have the advantage over onion seeds that you can start harvesting onions earlier (approx. 4 weeks earlier). You also have less effort. However, the selection of onion sets is significantly smaller than that of onion seeds. Onion sets are also significantly more expensive than onion seeds. Sowing onions often ensures healthier growth and the harvested onions can usually be stored for longer.

Sowing onion seeds

Summer on ions can be sown outdoors from mid-March to early April. Winter on ions can be sown in the bed from mid-August to September. The sowing depth is approx. 1 - 2 cm and the germination temperature is between 5 - 15 degrees Celsius.

Preplanting onions

To propagate onion cuttings, you can sow them indoors from January in seed trays or pots with moist potting compost. To ensure an even temperature and humidity, cover the seeds until germination. After around 6 - 8 weeks, as soon as the 3rd - 4th leaf is visible and no more heavy frost is expected, the young plants can be planted out in the open. The advantage of pre-grown bulbs is that they are less affected by plant diseases in the bed, weeds or pests.

Planting onion sets

Onion sets are small, pre-grown onions that can be planted directly in the bed. They are usually less complicated to grow and offer the advantage of a quicker harvest. However, the selection of varieties is smaller and onion sets are more expensive than onion seeds. Popular onion sets include the Stuttgarter Riesen, Red Baron, Rote and Birnenförmige varieties.

Planting onions - location & soil

Bulbs prefer a sunny location, preferably open to the wind, where they receive at least 6 hours of direct sunlight a day. The soil should be loose and well-drained to avoid waterlogging. This can lead to rotting. In addition, you should not plant the onions in a place in the bed where onions or other allium plants (e.g. garlic or leeks) have already been planted in the previous 1-2 years. A humus-rich, nutrient-rich soil is ideal for growing onions. Onions are weak to medium feeders and are less dependent on nutrients before planting.

Planting bulbs

Spring onions can be planted in the spring, around February or March, while onions are usually planted in the fall (September to October) or spring (March to April). When planting and selecting onion varieties, you should also bear in mind that not all onions can be stored for a long time. The shelf life depends on the variety and species. When selecting the variety, you should therefore consider whether you want to use your onions directly or store them.

When to plant onions?

The best time to plant onions is in spring (March/April) or fall (September/October), depending on the onion variety. Pay attention to the information on your seed packet or packaging, which will give you information about your specific variety.

How deep to stick onions?

The planting depth for bulbs or onion sets should be around 2 - 5 cm. Make sure that the root side of the bulb is facing downwards and that there is enough room for the tip to grow. Press the bulbs lightly into the loosened soil and then cover them with a thin layer of soil. The tip should still be slightly sticking out of the soil.

Planting distance for onions

The optimum planting distance for edible onions is around 10 - 15 cm within the row and 20 - 30 cm between the rows. Spring onions can be planted closer together with 3 cm between the plants and 15 cm between the rows. This will give your onions enough room to grow and pest transfer is less likely. Water the bulbs carefully after planting to anchor them well in the soil and encourage root growth.

Pro tip: If you soak onion sets in water for a night before planting, they will be heavier and won't be pressed over the soil in the bed. This can happen in damp conditions. They will also grow faster and develop their roots more quickly.

Fertilizing & caring for onions - what you should consider

Onions need a nutrient-rich, well-drained and humus-rich soil. Before planting in the fall, you can mix compost or well-rotted manure into the soil. This is particularly useful for sandy soils. However, you should avoid this while your bulbs are growing, as an excess of nitrogen can lead to increased foliage growth at the expense of bulb formation. Even moisture is ideal. You should avoid waterlogging to prevent rotting. When growing onions, it is also important that you regularly remove weeds from around your onion plants.

Onions: diseases & pests

Onions can be attacked by various diseases and pests. These include powdery mildew, onion fly, onion neck rot and thrips. To reduce infestation, you should observe the crop rotation for onions and maintain the correct planting distance. With good planting partners in a mixed cultivation bed, you can help to ensure that your plants are spared pests and diseases. You can find out more about mixed cultivation with onions in our article Onions: good & bad neighbors. To protect against onion flies, it may be worth covering the plants with crop protection nets.

Propagating onions

Onions are usually propagated using seeds or onion sets. With perennial onion varieties, such as winter hedge onions, you can also use bulbs for propagation. In the second year of cultivation, the onion plant develops a central, upright flower stalk that ends in a spherical, multi-flowered inflorescence. The flowers are usually white, pink or purple and are pollinated by bees and other insects. After fertilization, seed capsules are formed which contain the small, black onion seeds.

Harvesting & storing onions

Onions are usually harvested in late summer to autumn, as soon as the foliage has wilted and turned yellow . If you notice that your onions are starting to ripen, you should stop watering them. Carefully pull the bulbs out of the ground and leave them to dry in an airy, shady place for a few days. You can then store the onions in a cool, dark and dry room, such as a cellar or pantry. To prevent mold growth, you should not place the onions in direct contact with the ground and check them regularly. You can find out more about how to harvest onions correctly and how to preserve them in our article Harvesting and storing onions.

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Cover picture by Couleur on Pixabay.