Onion Growing Stages [Top Guide in 2023]

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The onion growing stages are bulb formation, germination, flowering, and maturation. During each stage, you should observe changes in plant growth to understand why a certain change may occur. In addition to the above stages, you should also take note of the onion’s nutritional requirements. To ensure maximum yield, use a balanced nutrition plan and use organic fertilizers. To learn more, click the links below. To start growing onions, use organic fertilizers and water your plants with a balanced blend of minerals and compost.

Onions are an excellent veggie to raise in the garden.. You can increase your knowledge by understanding the stages of growth.

In the vegetable garden, onions are common. It is important to understand how the stages of growth take place, as so much happens below the soil surface.

Check out our guide on growing onions.

How long does it grow?

Onions have a longer growing season than other vegetables. The longer growing season is due to the length of time it takes for plants to produce bulbs. It can take between 100 and 175 days for a seed to become a mature, dry bulb depending on the variety.

Onion Growing Stages

Gardeners grow onions in an annual crop similar to carrots. They harvest the bulbs when they are mature and the vegetative tips begin to die. However, Allium cepa is biennial. This means that it takes two seasons for a seed to germinate into a plant that can produce its own seeds.

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Let’s say you plant onions every year, but let’s break down the growth stages into separate seasons.

Year 1

The bulb development and top growth are the main focus of the first year of an onion’s cycle. These are the only stages that gardeners know about, as most gardeners harvest their bulbs within the first season.

Planting Onions

Onions are a cool-season vegetable, as we have discussed in our guide to growing them. Depending on where you live, onions can be planted at either the beginning or end of the year. For a late-summer crop, northern gardeners plant them in the spring. Southern gardeners plant them in the spring and fall.


  • Try to plant onions or transplants in your garden beds before you start spring planting. This is when the soil temperature stays above 28 degrees. This usually occurs in late March or early April, just before the last spring frost date. Plant the seeds 8-10 weeks before you plan to plant them if you are growing from seeds.
  • Fall planting should be done in August or September to allow them to grow for six to eight more weeks before the temperatures drop. They go dormant when the cold weather sets in and then resume growth in spring.

After you have planted your seeds make sure to keep the soil moist. The seed that germinates has both an embryo and food reserve in its protective seed coat. The seed’s seed coat is softened by soil moisture and the seed enters it through an imbibition process. The moisture once in the seed triggers cellular respiration as well as the metabolism of food reserves.

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Your seeds will germinate in a matter of ten days.

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Germination begins with the radicle emerging from the seed coat. It is also known as the primary root. As the first to emerge, it anchors the seedlings in place and supports them. The radicle absorbs nutrients and moisture from the soil, encouraging plant growth once it emerges.


The amount of water required will determine the level of success. Onion seed germination also depends on soil temperature. Onions need even temperatures, so be sure to keep the temperature even in your propagation tray. Onion seedlings should be approximately the diameter of a pencil when transplanted into the garden. If they do not sprout, you will need to plant them in a pot.

Onion Sprouting

The sprout absorbs nutrients and soil moisture and the first shoot begins to develop. It emerges from the softened seed cover. The shoot will naturally grow upwards through the soil to reach the sun, as gravity forces direct it. The seedlings shift their focus once the shoot has broken through the soil surface. They then focus on the development of leaves.

First  leaf shapes

Because the plant still depends on the endosperm for food, seedling growth is slow. The seedlings are trying to make leaves, as their food reserves are decreasing. The first real leaf emerges – a smaller version of the flat green mature leaves. The photosynthesis process begins, and seedlings produce glucose for food.

This stage of the seedlings looks like green onions. They can be harvested if needed.

Phase “Leek”

The plant’s ability to photosynthesize increases its growth rate at an impressive rate. Plant growth hormones are used to transform seedlings into new, undifferentiated leaves by turning them into new cells. Each new set of leaves stimulates growth and increases photosynthesis. The neck of the seedlings starts to thicken at this point.

This is the period between the formation of the first leaf and the appearance of four to seven leaves. Harvest leeks and small onions now if you plan to harvest them. Let the bulbs grow if you’re growing them.

Onion Bulb initiation

Growing onions is now focusing on bulb initiation. Light is the primary driver of bulb initiation. No matter the climate, plants must have at least four leaves in order to become bulb-ready. Each leaf grows into a shell, which eventually becomes a ring or sheath.


Different varieties can be classified according to how much sunlight they need to “set” their bulbs.

  • The longest-day varieties require 14-16 hours of sunlight to produce large bulbs. Long-day varieties require more time for leaf development before the bulb begins.
  • For short day types, you need between 10 and 12 hours of daylight.
  • Day-neutral types require 12-14 hours of daylight.

Bulb development

The onion plant ceases to produce new leaves after 8-12 leaves have developed and instead focuses its efforts on the bulb process. The leaves that have already been formed continue to grow and become longer, increasing the area available for photosynthesis. The central storage tissue for the bulbs is formed when the leaf sheaths expand.

The onions will then push the soil away, and “pop up” out of the soil.

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As bulbs reach maturity, they exhibit a physiological reaction called “tops down.” This occurs because raw materials are transferred from the tops (leaves) to the scales. The bulb size then swells. The tops of the leaves become exhausted and fall to the ground, meaning that the bulb is ready for harvest.

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Vegetative Aging

The water in the leaves freezes when fall temperatures drop to a severe frost. Fluid can leak from the cell walls because of the sharp edges of ice crystals. The onion tops fall to the soil surface because there is no structural integrity in the cell walls.

Year 2

Gardeners often don’t show their onions until the second season. This is because they aren’t familiar with the process of seed and flower formation. If onions aren’t harvested, and left to hibernate in their soil, they will grow again the next spring to set seeds and complete the life cycle.

Onion Growth Rate

Onions begin to grow again when spring temperatures rise. The bulb’s hormones cause cells to grow and lengthen, much like when germination took place in the previous year. The root system has developed sufficiently that the plant can concentrate its energy on sending up a shoot to break through the soil.

Flowers emerge from stems

The plants will start to grow as the weather warms up and the soil and air temperatures rise. The plant stops vegetative growth and quickly produces a flowering stem in preparation for its end. The stem becomes fully formed and the buds begin to grow. At the top, a purple or white flower blooms.

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Formation of seeds

Seeds are formed when the flowers of the round, showy flower heads are pollinated by bees, butterflies, or birds. All of the nutrient resources in the bulbs are transferred from the onion bulbs to the seeds. This creates the nutrient reserve that the seeds need for germination. The bulbs are fibrous and hardy when harvested right now.


The onion plant’s life cycle ends when the seeds are hatched. The onion has spent so much time developing seeds that there is very little room for plant growth. Plant growth hormones are used to induce genes that cause aging. There is no need for the plant to grow anymore, as there are very few resources available.

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Onion Growing Stages Conclusion

In general, onion can be used in all types of diets. It is also great for weight loss. It is high in fiber which aids digestion. If stored in dry areas and in open areas, onions can be kept for up to six months.

Onions, therefore, are a cold-season crop. They are grown from seeds in spring and harvested at the end of the summer. For the best growth of onions, temperatures should be between 60 and 80 degrees F/16 to 27 degrees C. Every plant requires at least 6 to seven hours of sunlight per day without any skips.

The onion plants can be grown in the United States and harvested. They thrive in areas with cool and long summers. Follow these steps to get your crops started. You will have a wonderful gardening experience and be able to harvest your onions from your own gardens and homes.

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