Onion Growing Stages:10 Different Stages of Onion Growth

The onion is a root vegetable that has most of its growth hidden in the soil. But have you ever wondered how onions grow? Starting from seed germination to harvesting.

Before growing them, I did have these questions. So, to uncover the truth, I delved into the science behind the growth. Whether you are a gardener or a learner who loves to learn new things, you have reached the right place.

Here, I have explained the onion lifecycle and the growing stages, which will help you to grow onions in your garden by providing the best-growing conditions for onions. So, let’s get started.

10 Different Stages of Onion Growth

Onions are available in many varieties such as red, white, and sweet onions having various shapes and sizes for example from small pearl onions to large Spanish onions. 

Onion plants do come under a biennial plant which means it takes 2 years to complete the lifecycle. During the first year, the plants are used to produce bulbs, and when they reach the second year they start to produce seeds. The approximate days taken by the plant to enter full maturity starting from planting to harvesting. 

If you are growing onions from seeds the whole process of growing onions will extend upto 16 months and they are used to take approximately 90 to 120 days to reach the maturity stage. Normally there are 13 onion growth stages which have their own unique characteristics.

Seed Germination:

  • The process of starting the seeding of the onions can be done indoors or directly sowing the seeds in the garden but for that, you need to look at the climate and the type of onions you are growing.
  • For example, if you are planting in a cool climate then I will suggest you start long-day onions indoors during late winter or early spring.
  • In the case of mid-summer harvest, you need to start seeds indoors at least 8 to 10 weeks before the last frost date, or outdoors you need to start as soon as the soil is workable.
  • You need to plant the seed about ¼ inch deep in rich soil and well-draining soil.
  • You need to maintain the ideal soil temperature of 75 degrees for onion germination.
  • If you are starting indoor seedlings you need to keep them underneath a grow lamp or in a place with a bright window.
  • Selecting a growing lamp for seed germination make sure to set up a daily timer as it may damage premature bulb development.
  • The onion seeds start to germinate within 7 to 10 days.
  • Starting the seeding of onions will impact the germination rate and growth rate of plants but starting too late in the growing season will expose the plant to high temperatures that will trigger development before they are ready.
  • Timing plays an important role in producing high-quality onions at home.
Onion Growing Stages:10 Different Stages of Onion Growth


  • The onions come under the category of monocots which means they are used to start with a single proto leaf which is called cotyledon and is used to look like a life blade of grass.
  • The foliage that used to appear after growing cotyledon is matured foliage.
  • You need to give them a consistent nitrogen source for growing them in full size.
  • The potting media that you add in seedlings does support for 2 to 3 weeks you need to wait to apply fertilizer unless the first leaves on the plant are grown or emerged on it.
  • Trimming of the plant during this stage does help to encourage more compact growth.
  • To trim the plants you need to make sure to use a sharp sanitized blade and according to an article from  Iowa State University, it is good to cut onions to 4 inches tall when the seedlings are grown for at least 5 inches.
  • In this stage, you can also thin out the seedlings in case it is grow a little crowded. 
  • I will suggest you leave at least 2 inches apart.

Vegetative Growth:

  • Now here comes vegetative growth where you need to focus on producing leaves such as bunching and bulb onions.
  • You need to maintain healthy foliage even if you are not choosing to harvest them.
  • The onions are used to store energy in their leaves which goes further into bulb development.
  • Balbir onion does have direct energy into vegetative growth.
  • The number of days between the sowing or transplanting and the stage of mature vegetative growth is not the same everywhere.

Bulb Formation:

  • In this stage when the daily sunlight reaches the length of the bulbing onion it will redirect energy from the vegetative growth and will help the bulb for initiation.
  • The whole process is implemented below the soil surface although you can notice some lifting or cracking of this soil during the process of bulb formation. 
  • Make sure not to disturb the plant in a way to check the progress of bulbing.
  • At last, the number of leaves and the size depend upon the utilized energy stored to create a bulb at the time of bulb initiation.

Harvesting Leaves:

  • After some maturation of the leaves and growing of onion bulbs, you can start harvesting leaves.
  • To complete the process you need to gently snip off 2 to 3 leaves from the matured onion plant at the base and you can use them fresh by storing them in the refrigerator.
  • According to me the best time to harvest the leaves is when they look in vibrant green color which is the most flavorful stage of harvesting them.
  • The process of harvesting leave can be performed daily which will help the plant to grow continuously and encourage them to produce new leaves.


  • Here comes the stage of maturation in which the bulb is fully developed.
  • In stage, the onion flavor, and texture in short the overall quality of the onion reaches its peak.
  • When the onion bulb gets mature the bottom of the leaves will wilt due to which the bulb will become firm. 
  • The bulb onion neck is used to get tough and fall over after reaching the matured stage.

Onion Harvest:

  • In this stage, you need to decide whether you want to harvest the bulb or leave the onion plants in the ground for the next year.
  • The process of harvesting helps to give access to fresh onions and if you leave them in the ground you will enjoy more extended onion growing.
  • The decision at least depends on the preference and need to harvest them or leave them in the ground.

The following are some signs that will give an idea that the onions are ready for harvesting:

Yellowing Tops: If you notice the turning of onion plants to yellow and start to droop it means the energy of the plant is diverting from leaves to the bulb which is the first sign of maturity.

Bulb Size: You need to check the size of the bulb by digging it around the base so that you can see the bulb formation. The bulb size of the onion is used to depend on the variety of the plant.

Vegetative Senescence:

  • In case you choose not to harvest them you see several changes till the winter.
  • The foliage of the onion starts to show signs of senescence that give a sign of the aging of plant tissues.
  • When vibrant green leaves start to turn yellow and start to wither which is an important process for the onion plants life cycle.
  • There are many reasons behind the growth of senescence the first factor is when the plant no longer can photosynthesize which is due to less amount of daylight. The second factor is when the plant starts to store energy for the next growing season. Lastly, plants are used to prepare themselves for entering the dormant period.
  • Every onion plant is used to go through a vegetative process. If you want to help your plant in the stage you need to cut all leaves from the base of the plant so that it does not spread disease and the plant is used to remain undisturbed during the cold months.

Year 2 Vegetative Growth:

  • After passing dormant in the winter they will start to grow in the spring season which is known as year two vegetative growth.
  • In this stage, the onion plants are used to produce new leaves which are the same as the leaves that are grown during the first year but are larger in size.
  • The plants are used to grow in continuity when they reach upto maturity.


  • The onion plants which can be eaten are used to produce white umbel flowers that are used to grow in cluster form.
  • You will see here onion flowering begins to form papery buds from the central stalk that you need to cut off.
  • The onion plants come under the biennial category and are used to grow naturally in the second year. 
  • It undergoes a phenomenon known as bolting and there are many factors such as extreme heat, and cold, that can trigger early flowering.
  • In case you see any bolting sign it means it is using valuable energy for creating flowers and seeds.


  • The onion flowers are used to self-fertile but cross-pollination is required for seed production when the male part of an onion flower starts to shed the pollen into the female part and make it ready to be fertilized.
  • Insects and winds play a very important role in pollinating onions. 
  • If you are growing onions for seed collection, keep in mind that alliums with the same species need to cross-pollinate.

Seed Formation:

  • After the successful completion of pollination, the seed starts to develop over the next few weeks by increasing in size and weight.
  • The seed will develop the outer shed hard and fall to the ground further which will germinate in the spring season.
  • You can harvest the seeds when they are fully matured and dry when they start to change their color and texture.

The following are some steps you need to follow for harvesting onion seeds:

  1. You need to wait unless the seeds turn to black and get fully dry.
  2. Next, you need to shade flower heads so that the seeds get released.
  3. You need to collect seeds in a paper bag or container.
  4. After collecting them you need to store them in cool and dry places so that they get ready to plant.

Plant Senescence:

  • The Senescence is used to grow in the final stage of the plant life cycle.
  • The formation of Senescence is used to get a trigger by combining all the completion of the reproductive stage, the depletion of nutrients, and environmental conditions such as cold weather.
  • When a plant enters to senescence stage it will begin to yellow and brown withering and collapsing.
  • In this stage, the seeds on the plant will get dispersed by wind, animal activity, or human intervention.
  • It is a natural part of forming the senescence of the onion plant life cycle.


Hence I will conclude here that if you really want to grow the onion plant in your garden you need to know about all the stages they are used to going through so that they are grown in a healthy way that you can save them for further production also. 

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