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How to grow onion?

January 15, 2021
Growing onions at home

Raw or cooked, dried or fresh, onion is a staple in any kitchen. If you are interested in growing your own tasty and organic onions at home , take a look at the guide below.

Growing onions at home

Growing onion is easier than many think. Can be made from transplants , sets or seeds1.

  • The transplants are seedlings of the current season , which are usually for sale in nurseries.
  • The sets are immature bulbs that have been grown the previous year; They are usually the easiest to plant, the first to harvest, and the least susceptible to disease.
  • For its part, growing onions from seeds offers the advantage of being able to have more varieties, but you should bear in mind that the crop can take up to 4 months to mature. For some beginners this can be quite a challenge, but even so, seeds are still the most popular form of home growing.

Before purchasing any of these options, make sure you know the variety’s ” day length ” (short day or long day), as the length of the day affects how and when the onion bulbs will form. The onions short day begin to form bulbs when the days are 10 to 12 hours; these are suitable only for southern latitudes. Long -day onions need 13 to 16 hours of light to form their bulbs; they are the most suitable for growing in northern latitudes.

Onions like cold weather in the early part of their growth, which is why it is recommended to plant them in the spring. Generally speaking, they grow in cold weather and form bulbs in hot weather.

Climate and Soil

Like any other crop, onions need specific climate and soil conditions to grow successfully2 3.

What is the best soil to grow onions? Onion can be sown in almost any type of soil, except heavy and dense clay. In general, a permeable , deep and light soil is considered to offer the ideal conditions. You can always resort to the use of a fertilizer or compost to achieve these characteristics, as well as to improve the fertility of the soil. Adding compost is a highly recommended step to provide nutrients and grow larger onions.

Soil preparation

You will need to:

  • Hard rake (you must rake the soil before planting)
  • Trowel (for clearing weeds and planting onions in the ground)
  • Compost (mixing the soil with a little compost helps increase the level of nutrients in the soil)
  • Fertilizer (Optional)


  1. First, make sure the ground is free of weeds and rocks.
  2. Loosen the soil with a rake (30 cm deep minimum), and mix it with a compost bag. If you want, you can also add a little fertilizer in this step. Note: If you want to grow organic onions , avoid using fertilizers or other types of plant food.
  3. Go back to raking and flatten the soil with the head of the rake or with the help of your own foot.

What is the best climate? Onions love to grow in sunny areas , where they receive a lot of light. As we said before, they tolerate cold temperatures well in the first phase of growth, but they need sunlight as the bulbs form . Most varieties do well in full sun, with temperatures around 15 ° C or 59 ° F. A good time to sow onions are the months of February or March, hence they can be harvested in late spring or early summer. Depending on the region, it is also customary to sow in late summer / early fall, or during winter ( starting indoors ).

Sowing and Irrigation

Regardless of whether you are going to sow seedlings, clusters or seeds, the indications are usually very similar.

Assuming you already have the soil ready, here is a quick guide on how to grow onions in a patio or garden :

  1. Make 1 or more straight furrows in the ground, making sure to leave a gap of approximately 25cm between them.
  2. In each row or groove, start making holes approximately 2.5cm deep, leaving 10-15cm distance between them.
  3. Insert the bulb or seed into the hole and cover with soil. If you are planting sprouted onion plants, make sure the green sprout protrudes a few millimeters above the soil surface.
  4. Finally, press the soil around to make it firm and water lightly.

Keep in mind that growing onion requires light but constant watering . That means that you must keep the ground moist, but without causing excess humidity. For this, it is recommended to maintain a low and frequent irrigation volume.

One of the best techniques is to cut a small trench between each furrow and fill it with water; This helps keep the onion roots supplied, without soaking the soil surface or favoring the germination of other seeds. Onions cannot compete well with weeds , which is why it is so important to direct water only towards their roots.

Expert farmers always advise suspending watering completely about 20 days before harvest.

Growth and pests

If you’ve sown seeds, germination will likely occur after a few days. If you have planted seedlings or clusters, the stems, bulbs and roots will continue to develop as the weeks go by.

  • Remember to keep watering light but constant, especially if you live in a very dry climate.
  • If you are using fertilizer, you can apply it every 3-4 weeks, as indicated on the product label.
  • Keep the growth of other plants in the field at bay, periodically eliminating weeds that may appear.

Like the vast majority of vegetables, the onion crop can be affected by different pests and diseases . Some of the most common are4:

  • Trips onion. Thysanoptera that produces pitting, deformation and discoloration of the leaves
  • Onion fly . It affects the flowers and green parts of the plant, but it can also damage the bulbs irreversibly.
  • Onion miner worm . The larvae make galleries in the leaves of the onions.
  • They affect the bulb and its roots.
  • Onion charcoal . It is characterized by causing longitudinal silvery lesions, which later develop into carbonaceous pustules.
  • Onion rust . It causes small, reddish pustules on the leaves.
  • Soft rot . It causes rotting of the neck of onions.

Among the most used prevention and control measures are:

  1. Inspect the crop regularly to identify alarm symptoms in the crop.
  2. Remove affected plants as soon as possible to prevent the problem from spreading.
  3. Disinfect the seeds before transplanting.
  4. Do not grow the onions in the same field for several consecutive years.
  5. Avoid excess humidity in the land.
  6. Resort to the use of specific pesticides according to the type of pest or disease in question.


The onions will be ready to be harvested after 3-4 months . The yellowing or drying of the leaves is the signal that tells us when the crop is almost ready for harvest. At this point it is recommended to bend or split the necks of the leaves to prevent the sap from flowing to the stems; thus the energy of the plant is concentrated only in the maturation of the bulb.

1-2 days later, when the leaves have completely turned brown, carefully loosen the soil around the onions to partially dig them up; Leave them on the ground to finish maturing in the sun . After several days, you can already loosen all the soil and dig up the onions completely.

But it is not yet time to collect them. Now you should wait about 2 weeks for the onions to dry on the ground. Some people tend to place the dried leaves in one row over the bulbs in the next row to prevent the sun from burning them.

Once dry, the onions are ready to be harvested and stored . Remove the dirt, excess dirt, and place them in a cool, dry place to continue developing their flavor. Dried bulbs will keep very well for about 4 months – 1 year.

It may interest you: Onion – Types, Characteristics, Properties, Benefits, Contraindications and More

Quick answers to Frequently Asked Questions

How to grow onions in pots?

The onion can also be grown in pots when we do not have a garden or patio. In this case, it is important to choose the pot or container in question well, since it must be at least 30cm deep and 30cm wide.

Taking into account all the characteristics and requirements of this crop, here is a brief 4-step guide to growing your own onions in a pot :

  1. Fill the pot with clean and loose soil, much better if it has been mixed with some type of compost previously.
  2. Insert the seeds ( several ) or the bulbs ( only 2 ) to a depth of 2.5cm, trying to leave enough separation between them. Cover with soil and water. Note: the green bud of the bulbs should protrude slightly.
  3. The seedlings need sunlight and a little water on a daily basis.
  4. After several weeks (almost 3 months), when the onion leaves are deep green, it is time to harvest them.

How can I collect my own onion seeds?

To collect your own seeds you need to wait for the onion plant to flower. Some hobbyists allow only 1 or 2 plants to flower, as this is more than enough to get a good supply of seeds for the next harvest. A plant can produce between hundreds and thousands of flowers, and it is possible to collect up to 6 seeds for each one.

What is better: growing onion with or without seeds?

While it is possible to grow the same onions by planting small bulbs or from seeds, many hobbyist farmers prefer to avoid seed because growing them can be riskier and time-consuming.

What is the best compost for onions?

The main recommendation when using fertilizers for onion cultivation is to choose one that offers a good concentration of phosphorus and potassium , but a moderate concentration of nitrogen . Excess nitrogen results in onion bulbs that are more watery and prone to poor preservation.


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My name is Louise Hammond, and I am the creator of this website, a place to find information about tubers, bulbs and medicinal roots. In I show the properties, benefits, characteristics, photos and images, ways of growing and how to make delicious meals from starchy vegetables.