Complete grow guide for onion cultivation


A lot of time has passed since we started the crop files and we still hadn’t dedicated time to growing onion , so today we are going to dedicate it entirely to telling you the ideal way to grow onion the way we usually do it. It is an essential lily in the kitchen and as an ingredient in any meal. So you just need to cultivate it.



The onion is a lily ( Liliaceae ), like leeks , garlic , chives, etc.). They have the particularity that they can be grown in various stages throughout the year, and can be stored for a long time, so we can have them 365 of the year. Since medieval times it has been attributed healing properties, and even in the 21st century we have the same idea and even tablets with onion concentrate are marketed.

Its origin is not exactly known, but most botanists place the origin of the onion in the area of ​​Iran, Pakistan, etc. Its spread was rapid to other areas, where it was transplanted and cultivated in traditional gardens.

Purple Onion. Photo by Danny Ayers

Because it is such an appreciated crop, we are going to give you the keys to its cultivation.


The best conditions for onion development are  full sun.  In its early stages of development, it tolerates low temperature conditions, but once the bulb develops and acquires size, temperatures have to rise, according to the arrival of spring (early varieties) or autumn and the departure of summer (late varieties ).

If we had to provide values, we would say that the optimum temperature range for onion cultivation is from 15ºC. Of course, it also depends on the variety. Most commonly, most varieties require temperatures to be above 15 ºC in all phases of cultivation, but there are other varieties that require cold periods at the beginning. However, it is not the most common.


To achieve optimal development in onion cultivation, light , permeable , spongy , and deep soils are required , since it is a bulb. That it is spongy and permeable, as we have once commented (are we perhaps very heavy?) It depends on the nature of the earth, but it can be corrected, more or less, according to the contribution of compost .


Well, think that the root system of the onion is quite deep, and it can go up to 60 cm deep. Although we cannot carry out such deep soil work, we must give great importance to the first 20 cm, as it is where most of its entire root system develops.

Nothing more than this technique reports large and quality bulbs.

As for the pH of the onion , which we have recently commented on, its range is between 6.5 and 7. The best thing is that the soil is slightly acidic.


Irrigation must be constant, but it does not need a lot of water. It seems that lately we tend to say a lot about constant watering, but in this case, in onion cultivation we require it more than ever. In fact, we put it in another color, the onion does not tolerate excess humidity,  therefore what must be done is less volume of irrigation but more frequently. Do not let the soil dry out and when we realize it add a very abundant watering and ale, to watch TV. This produces cracking and rotting .


In autumn a good amount of compost is added on the ground. It is required to be decomposed, meaning that there has been a lot of time in the stack forming and it has finished the process. Onions ask for a good amount of potassium and phosphorus, but just the right amount of nitrogen. Take a look at the 20 types of fertilizers , in which we mention the amounts of minerals (potassium, magnesium, nitrogen) in each one.


Seedlings: it  is sown in February, in controlled environmental conditions (greenhouse, indoors, etc.), or in April, when the temperature rises, outdoors. Usually 25 cm between rows and 25 cm between onions. In the case of early sowing,  already in the open air and not indoors as we have commented before, it is sown at the end of March.

Winter Onions –  We said at the beginning that there were early and late varieties. In this case, the winter onion is sown in the 2nd half of August (with the same planting frame).


Although growing onion is easy because obtaining seeds in sachets is very easy and cheap, if you want to collect your own seeds , you will have to wait for the plant to flower. About 6 seeds are obtained per flower and between 50 and 2,000 flowers are produced (imagine the number of seeds per plant). They are black and have a triangular shape.

Onion flower

Here we tell you a trick to be able to sow onions in home seedlings . (trays, yogurts, pots, etc.):

 A few seeds are sown in seedbeds, with compost or some type of substrate. It should be kept moist but not wet, and covered with newspaper, glass or plastic. When the first shoots appear, these newspapers or plastic are removed and light is provided, at a temperature of 20 ºC. When they start to grow and the first leaf measures more than 1 cm, the seedlings are separated into different containers, using the same type of substrate. When the plants grow and develop, they can be arranged in open air conditions, but in a sheltered place. Until spring, when they are definitively transplanted.  

You can also have the classic onion seed envelopes in case you do not arrive on time for their collection date. The calendar above can help you know when is the best time to plant.


  • The garden where the onions are grown must be kept free of weeds at all times.
  • In the period before harvest, a mulch is recommended in which you can take advantage of the herbs that you have removed.
  • In the event that some plants bloom, they stand out when they have not yet grown enough. If we let it bloom, the bulbs will not finish forming well.
  • When the vertices of the onion leaves begin to turn yellow, the necks twist and break, and the onion is lifted a little off the ground to dry the head. Then, after 2 or 3 days, they are completely removed and left to dry in the sun.


Onion varieties Photo by: Alexis Lamster

Cebollas de primavera:   Stuttgart giant, pear-shaped, jeweled. Jump, Babosa

Winter onions:  Express Yellow, Weisse Frühlingszzwiebel Senhyu Yellow.

They are traditionally known as the yellow sulfur onion from Spain  and  the giant from Spain.

Cebollas de plantación:  Stuttgart giant, pear-shaped, jeweled.

Winter planting onions:  Presto, Romy.


Pay special attention to the following “bad friends” when growing onions.


  • Trips
  • Miners
  • Onion moth
  • Onion fly


  • Nematodes (for example,  Ditylenchus dipsaci )
  • Root and neck rots ( Pythium spp, Phytophthora, Rhizoctonia, Fusarium, Pyrenochaeta,  etc.)
  • White rot ( Sclerotinia )
  • Pink roots ( Pyrenochaeta terrestris )
  • Mildew ( Pyrenochaeta terrestris )
  • Botrytis (Botrytis)
  • Coal ( Urocystis cepulae )
  • Stung ( Stemphylium vesicarium )
  • Purple spot ( Alternaria porri ).

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