Onion Growing Stages: How fast do they grow?

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A lot happens underground including the growth of onions. It’s not hard to know when they are ready and if you understand their growing stages, you can better prepare for them. Here are all the different steps it takes for onions to grow.

Onion growing stages: Onions begin as seeds or small bulbs and need soil, moisture, and sunlight to germinate. After this, the onion produces a stem and leaves which take in sunlight and transfers energy to the bulb. After the stem grows, it is the bulb’s turn. When the leaves turn yellow and fall over, the onion is ready for harvest.

Onion growing stages


There are different methods to starting your onions out. While you can plant seeds you can also plant small bulbs.

These bulbs need cooler weather to start, so you can plant in early to mid-spring. Seeds, on the other hand, take more time, so you can start them indoors before transplanting them outdoors.

Onion seeds should be planted pretty shallow as they are small and need to be close to the surface. Onion bulbs can be a bit deeper but again, don’t plant them too deep, or else they won’t be warm enough.

The germination process for onions includes access to warmth and moisture. It can take about two weeks to start the process and for a stem to emerge from the seed.


The germination process takes place underground but soon leads to a stem and a few leaves popping up from the soil. Meanwhile, the onion will start to grow roots to allow it to take in more nutrients.

This period is crucial as it will establish a solid foundation for growth. The soil should be kept moist and loose enough for the small roots to spread out.

Onions are considered seedlings for just a short period of time. Basically, this stage takes place between the first bit of growth above ground and then the stem has up to eight leaves.

Vegetative Growth

The vegetative stage happens quite quickly and can be fascinating to watch. Above ground, the onion stem branches out to take in as much sunlight as possible.

These leaves are critical to the growth of the onion underground as they transform sunlight into energy. Without this stage, the onion won’t have enough nutrients to properly grow the rest of the bulb.


Now that the onion is developed above ground, it’s time for growth to happen below ground. It can look like the onion is ready for harvest when in reality, things are just starting in the soil.

Thanks to the leaves above ground, the bulb can start to take shape. Slowly, layer upon layer is created as the onion becomes larger.

The maturation process can take a few months but after a few weeks, you can start to see evidence of it. The top of the bulb will start to push through the soil as it grows.

Even though the onion is growing, it is still not ready yet. Keep it watered and side-dress with compost to ensure it has enough nutrients.


Finally, after patiently waiting, your onion will be ready for harvest. There are many clues that onions are ready for harvest and if you pay attention, you can find the optimal time to do so.

First, the bulb will push up further through the ground, giving you an indication of the size of it. Onions will vary in size by variation, so some will naturally be small and some will be large.

Another sign your onion is ready is by the leaves and stems. These will start to turn yellow and fall over.

When onions are ready for harvest, they will stop growing, so there is no need to wait. If you are unsure about your onions, you can gently remove one from the garden as a test.

If there is enough room in the soil, gently dig around the onion then slowly pull it from the ground. Don’t pull too hard or else the tops will fall off.

After you remove the onions, lay them out in a covered place that is cool and dark. This will harden the outer layer of the onion, which in turn protects it.

Allow the onions to dry out so there is no moisture left. Then, the onions will be ready for storage and won’t grow moldy.

If you have a lot of onions, leave the tops on them and braid them. You can then hang them to allow for more air circulation.

An alternative is to store loose onions in a box. Keep it in a dry, cool place, and the onions will last for a few months.

How long do onions take to grow?

It can take between 80 and 100 days for onions to fully grow. This is a long period of time, so be sure to have enough garden space to accommodate them.

You can get a head start on onion growth by planting the seeds indoors and then transferring them to your garden as seedlings. Still, don’t expect to harvest your onions until late summer.

How do you know when onions are grown?       

The best indicator that onions are fully grown is when their tops turn yellow. They will also flop over as the energy in the plant goes to the bulb and not the greens.

Larger varieties of onions will also start to pop out of the ground a little so you should be able to see the tops. You can gently brush the dirt off of these tops to see how large they are and their progression of growth.

Generally, onions are ready for harvest in late summer, around August. Onions won’t continue to grow when they are ready, so once you see these signs, harvest them so pests and diseases don’t have a chance to infiltrate your crops.


Onions have a clear set of steps for growing. After the seeds go into the ground, stems start to grow in order to transfer nutrients to the rest of the plant. Then, the bulb starts to grow and after a few months, the whole onion is ready for harvest.

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