Onions from sowing to harvesting

Onions are an indispensable vegetable in the kitchen: many recipes and sauces could not be done without this vegetable. This is why it is also a vegetable that cannot be missing in a self-respecting vegetable garden, a flowerbed dedicated to the cultivation of onions is a must.

As a plant the onion (Allium cepa) is part of the Liliaceae family, a relative of garlic and asparagus, it is a bulb vegetable, which we grow in an annual cycle.

From the golden onion to the white one, passing through the famous Tropea red onions there is certainly no shortage of onions to sow. In fact, there are different varieties of onion, characterized by different colors but also and above all by a different crop cycle. We, therefore, find winter onions and onions to sow in spring, and we have the opportunity to have onions in the garden almost all year round.

Here I will give you a comprehensive guide to organic onion cultivation, from planting to harvest. Those looking for quick information will find the summary sheet at the end of the article, with a summary.

Climate and soil suitable for onion

Climate. This lily plant resists the cold very well, so much so that it can be planted in autumn and wintered in the field. What he does not like are too strong climatic excursions. It prefers sunny areas.

Soil preparation. The most suitable soils for the onion plant are those that are ventilated and not very compact, with a pH between 6 and 7, while it finds difficulty in clayey and asphyxiated soil. Above all, it fears water stagnation, a source of rot and disease. Since onions require loose soil, it is essential to implement good soil cultivation, to be carried out the months before sowing, by digging. Deep tillage is not essential if the soil is already draining, but it is important that the earth does not remain compact.


Onions are undemanding plants in terms of nutrients and in particular, they do not like recently fertilized soils and excess nutrients. For this reason, it is good to avoid specific fertilization before planting, better to feed the soil a few months before sowing and without exaggerating. An excellent system in a mixed garden is to insert the onion in a crop rotation following a demanding vegetable in terms of substance, such as pumpkin or courgette, in this way our lilycea will be satisfied with the residual fertility left from the predecessor vegetable.

How and when to sow onions

Planting onions is a very simple operation, which can be performed at different times of the year, depending on the variety of onions chosen, and also in different ways, starting from the seed, the bulb, or putting the seedling.

The three ways to get started

There are three ways to plant onions in the garden: onions can in fact be sown by planting the seed directly in the garden, always sowing from seed to seedbed and then transplanting the seedlings or planting the bulbils in the ground. The latter is not real sowing, since the seed is not involved. If sowing in seedbeds, onions are transplanted after about 1 month and a half or two when the seedlings are 15 cm in height.

The ideal is to start from the seeds, placing them directly in the ground and avoiding transplanting, which the onion plant does not particularly like. The clover is a very convenient method and is generally cheaper than buying the seedlings in the nursery. It can be a good idea for those who do not have the time or desire to follow sowing from the beginning.

Sixth of implant

Onions are grown in rows 25-30cm apart, leaving about 20cm between each plant. In reality, this measure is very indicative and refers to the classic bulb onions: if we decide to grow spring onions, which are harvested for the leaves, we can reduce the measure to halve it. The planting size also varies depending on the variety, for example, the Borettane onions that remain small are sown very close together.

Keeping a regular space between the rows is important to be able to weed with a hoe or weeder, which is also useful for aerating the earth, especially if the soil tends to compact. So when sowing and transplanting, always remember to pull a thread or in any case make parallel and straight furrows.

Varieties and sowing period

Onions have different varieties with different growing periods. Generally, the red onions are early, the white semi-early, and the golden onions late, although several exceptions to these rules have been created with the selection. The sowing periods are different and there are winter varieties and spring varieties, it is important not to make mistakes because there is a risk that the plant will mount to flower, ruining the harvest. Those who want to learn more about the topic can read the article on onion sowing, which better explains the period, distances, and suitable moon phase. In any case, always remember to buy a seed suitable for our climate and the period in which we want to sow.

Winter onions

There are varieties of onion, especially used for fresh consumption, which are sown in September and transplanted in November, after winter they develop the bulb that can be harvested in April or May. If you choose to plant winter onion bulbils, you can do it in November. Generally, the winter sowing is done for golden onions or white onions.

Summer onions

The summer varieties are sown in late winter (in February in seedbeds, while between March and April they are transplanted in the garden), in February or March to plant the bulbils. They come ready in summer and generally keep longer. Summer onions can be of any color: white, golden, or red.

Spring onions

The spring onions are botanically always onions, grown for the leaves rather than for the bulb. Just like the bulb onion, they can be grown from autumn to spring (sowing October or November) or from spring to summer (sowing between March and April).

When to sow Tropea red onion

The Tropea red onion variety is today among the most requested and appreciated, both for its flavor and for its digestibility and therefore one of the most requested onion seeds. It is a classic summer onion, to be sown from February in the seedbed or from March in the field.

The cultivation of the onion

Growing onions is not difficult, once the soil is well managed and the right irrigation is guaranteed, this vegetable can give great satisfaction to even the inexperienced farmer.

Weed and hoe the soil

Weed control. Weeding is important to defend the onions from weeds, the onion plants do not cover much of the surrounding soil and for this reason, they can struggle to compete with spontaneous vegetation. Good weed control ensures that our crop has adequate space and nutrients available to develop well and enlarge the bulb.

Hoeing. Oxygenating the soil and keeping it loose is very important, my advice is to hoe at least 3-4 times during the cultivation of onions to break the crust of the soil, but be careful not to damage the roots. If you have clayey soil, go even more often.

A very useful tool. A good way to get through the rows to do this job is to use the clod breaker with an oscillating blade, a tool that deserves more consideration. The tool is very simple: a crusher wheel in front that moves, followed by a blade that passes a few millimeters below the ground level and cuts the herbs under the collar. However, I renew the recommendation: if you go too close to the plant we risk cutting off the most superficial roots of our onions.

Mulch. Those who do not have time to weed the soil regularly and want a vegetable garden that requires the shortest possible time can opt for mulching the soil, using a cloth or straw. Onions, for their sixth of the plant, are particularly suitable for the use of straw, a natural and biodegradable material at no cost. Mulching also saves on irrigation, since the soil cover helps retain moisture.


Onions are not very demanding vegetables in terms of water, they should be watered only when the soil is completely dry, being careful not to overdo it since the onion roots, rather superficial and rot in case of stagnation. During the summer it is especially important to prevent the soil from drying out and hardening under the sun, so we intervene regularly by wetting. In many cases, a drip irrigation system becomes useful.

The cultivation of spring onions

Spring onions differ from onions as a vegetable. They are harvested in a different way and above all because in the kitchen they have a different use, more similar to that of leeks. However, as a plant we are always talking about Allium Cepa, they are simply varieties that tend to enlarge the bulb a little while making tender leaves, very suitable for consumption. The difference between the classic onion and the spring onion is all in the harvest: from the first, we take the bulb, from the second we take the plant practically whole.

From the point of view of cultivation, the spring onion requires some special precautions:

  • We can fertilize with a little more nitrogen, in order to favor the leaves.
  • If we believe in the moon phase, the spring onion we can put it in the growing phase, instead of in the waning phase like the onion.
  • During the cultivation it is useful a hock, to make the stem whiten better.
  • Water must never be lacking, otherwise the stem becomes fibrous.
  • We harvest earlier than the onion, with the plant still vegetative and the leaves tender (usually after 70/90 days from sowing).

Grow onions in pots

For those who have a garden on the balcony, onion is certainly not the best choice: you need a large pot but you get a very poor harvest, which certainly does not justify the constant watering work.

So the advice is not to grow this vegetable on the terrace, but to use the space for other vegetables that can give greater satisfaction.

Adversity of growing onion

Onions are resistant to horticultural plants, little subject to parasites and diseases, and therefore very suitable for organic cultivation. Some general measures allow you to prevent most problems:

  • Crop rotation: onion should not be grown on plots in which another lily plant has previously been grown (therefore other onions, garlic, leeks, shallots, asparagus).
  • Associations. Combining onions and carrots, as we will see, is good for both vegetables.
  • Correct tillage of the soil. It is very important to guarantee the onions excellent water drainage, this greatly reduces the onset of diseases.
  • Care of irrigations. In particular, we avoid excess water, which favors harmful rot.

Insects harmful to onions

The onion fly is the insect that represents the biggest problem for this crop. To drive it away in a synergistic garden, the best way is to combine carrots and onions, carrots are natural repellents for this fly.

Other pests can damage our Allium Cepa crops, so we have published a guide dedicated to recognizing them and also fighting them with only natural methods.

Diseases of the onion

Worse than insects some diseases can destroy plants, in organic farming the remedies can counteract the spread, but not cure the affected plants. Prevention and monitoring are therefore essential, starting with having draining soil.

Downy mildew is the most fearful disease that can affect the onion plant, it is a fungal disease that can be recognized by observing the leaves become greyish, then turn yellow and dry. In this case, it is necessary to treat it with copper to prevent the spores from attacking the bulb. The effect of onion blight is not to make the bulb last, which quickly rots before or after harvest.

The roots of the onion plant are very sensitive to water stagnation, a typical adversity of this cultivation is root rot, so be careful in dosing the irrigations.

Those who want to know more about onion and spring onion diseases can find an article dedicated to the topic, which highlights preventive precautions and biological treatments.

Early seed mounted

If the weather conditions are bad, the onion plant can play the trick of going to seed early. It is not a disease but it is still a very bad event because it spoils the harvest, it must be avoided. I refer you to an in-depth study on onions that grow in bloom, where I try to explain what can be done if the onion blossoms too soon and why this can happen.

Collect and store onions

Onions are a vegetable that can be kept practically all year round, as long as you pick it at the right time and then know how to store it correctly. We collect by exploiting a dormancy period of the bulb, which therefore remains inactive without germinating for a few months.

If the onion is not kept properly it rots or sprouts, trying to give life to a new plant. In the latter case, you can also choose to plant it, to obtain fresh spring onions.

The collection

Onions would be a biennial plant, in the garden it is grown as an annual, avoiding the formation of seeds. The onion harvest must be done without waiting for it to flower.

We can understand that the onion is ready to be harvested when the “cane” of its aerial part bends by itself. The harvesting period is also understood by the yellowing of the stem. Harvesting must always be done before they begin to mount and develop the floral scape. While waiting we also give the bulb time to enlarge.

The onion bulb can always be harvested, in the sense that it is edible at any time, but you have to wait for the plant to dry out for it to be stored for a long time. If we pick it up too early, its water content causes it to deteriorate prematurely and we are forced to consume the onion within a few days. We must therefore wait for the plant to dry out, this is the right time to seize it by ensuring proper conservation.

In the peasant tradition, the practice of manually folding the onion plant before harvesting is widespread. In my opinion, this work is useless, just wait for it to happen spontaneously. If someone has different opinions and above all experiences, he can write it in the comments.

The method of harvesting is very simple: the whole plant is removed to take the bulb which is partially buried.

We can decide not to collect some onion plants to allow them to bloom and get seeds (in-depth: how to preserve onion seeds)

Onion preservation

For correct conservation, as already anticipated, it is first necessary to grasp at the right time. If the unripe bulb is harvested even if it is then dried, onions will be obtained ready to germinate at the first humidity, while if they are harvested at the right time the bulbs resist for the entire period of dormancy and are preserved for a long time excellently.

As soon as they are harvested, the onions are left to dry for one or two days in the sun, then they must be stored in a cool and dark place, such as garlic. Traditionally, onions are tied together by the leaves by braiding, that is, forming braids that hang in ventilated places, such as the porches of the farmhouses.

The dormancy, on which the conservation of the vegetable depends, has a variable duration: 60-120 days depending on the variety. In general, golden onions last longer, while red onions such as the famous Tropea onions are less durable. For this reason, red and white are usually eaten fresh, while the golden ones are kept more for conservation. In a home garden, it is therefore convenient to have different varieties to eat onions all year round.

In addition to dormancy, the enemy of conservation is rot, which occurs in humid conditions. The fact of keeping the bulbs in a humid and ventilated place, as well as not overlapping them too much in the boxes serves to prevent the onions from molding or rotting.

Plant a sprouted onion

In October or spring, an onion may sprout, especially if subjected to a humid climate. The advice, in this case, is to plant it in the garden or even in pots, so it will produce the spring onions, which are harvested when they are the size of an inch, are sweet and tender, and eaten fresh.

Varieties of onion

The onion can be white, red, or golden. There are many varieties and also many characteristics according to which to classify them. The first distinction, also used in supermarkets, is color. In general, the colors are also indicative of the periods of growth: usually, the reds are early, the white semi-early, and the golden late. The types of onions can also be divided according to shape: there are long onions, elongated bulbs, or round, more spherical onions.

The onion varieties are also divided by the length of the crop cycle (days that pass between sowing and harvesting) and by the best sowing period. In this way, we identify early and late onions, and then winter and spring onions.

The dormancy is also different, which can vary between 60 and 120 days this is of interest due to conservation: the golden ones last longer (onions from Parma, Bologna, white onion from Milan,…) while the red onions (Tropea onion, Cannara, from Bassano…) last much shorter.

There aren’t just bulb onion varieties. There are also varieties that do not form the enlarged bulb and are consumed only fresh: they are the ones we grow to obtain spring onions.

Cultivation sheet at a glance

Onion (Allium Cepa)

Preparation: dig and hoe to obtain a loose and draining soil, no specific fertilization is required.

Sowing period:
Winter onions: October / November.
Summer onions: March / April

Sowing depth: 0.5 / 1 cm

Germination temperature: 20/25 degrees

Distances: between the plants 20 cm, between the rows 30 cm.

Methods: direct sowing, sowing in seedbeds, planting cloves.

Cultivation: frequent weeding or mulching is important.

Irrigation: after sowing or transplanting water regularly, when the plant is formed when needed. Never let the land be arid, but neither do they have excess water.

Main adversities: onion fly, downy mildew, mounted at the early seed.

Harvest: when the plant turns yellow or bends.

BACK TO THE TOP (and read the complete guide).

Recipes with onion

Tuna sauce with onions recipe/ Zucchini omelette with onion recipe/ Onion gratin recipe/ Onion flowers with herb dip recipe/ Salsiccia with roasted nuts and onions recipe/ Onion soup with gruyère bread/ Caramelized Onions recipe.

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