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How do I get my Onions to Grow Bigger?

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How Do I Get My Onions To Grow Bigger

It is recommended to commence the process of onion seed germination 10-15 weeks prior to the intended transplantation period, which falls between mid-February and mid-March. Onions exhibit a degree of resilience towards mild frost and can be transplanted into the garden during late April or May. While it is feasible to directly sow onion seeds in the garden as soon as the soil is workable in spring, it is important to note that the resultant onions may be comparatively smaller in size.

The objective is to maintain a weed-free soil environment surrounding onions through the application of a substantial layer of grass clippings, shredded leaves, or clean straw as mulch. Additionally, frequent and shallow cultivation between the rows of onions can prove to be an effective measure.

Here is our complete guide on how to grow big onions! In this post, we will teach you the most common reasons why your onions aren’t growing and share our secret for a big crop. We will also discuss how to grow this delicious vegetable in pots, water, and from scraps! So, without further ado, let’s start!

How do I get my onions to grow bigger?

Ok, now that we have analyzed the main problems, let’s talk about solutions.

Choosing the right variety

To keep it simple, onions are classified as short-day, intermediate-day, and long-day types based on the amount of sunlight they need to bulb. On average, short-day onions require from 10 to 12 hours of sunlight per day, intermediate-day onions need 12 to 14 hours, while long-day onions need from 14 to 16 hours. Keep this in mind when choosing your onion varieties.


Planting your onion too late usually results in extremely small onion bulbs, so you definitely want to get the timing right. If you are starting from seeds, you should begin the process indoors roughly in the late winter to then move your plants outside in the early or mid-spring. You can plant your seeds outside as soon as your soil is workable. If you’re using an onion set you can plant your bulbs directly outside when your soil is workable, ideally in the early spring. Remember, these vegetables tolerate light frost but should not be exposed to freezing temperatures. 


Of course, you should also make sure there is enough space between your onions. Keep your bulbs from 10 to 20 cm apart depending on how big you want them to grow. Of course, the closer they are, the smaller your onions will be.


Plant your onions in a sunny spot in moist but well-draining soil. These vegetables need roughly two to three cm of water every week. But don’t exaggerate, or your crop may rot. 

How to grow onions in a pot

But what if you don’t have a fancy garden bed to plant your onions? No problem! You can easily grow onions in pots.

  1. Plant plenty of seeds in a container roughly 15 cm in diameter and 20 cm in depth. In this first phase, onions need about 5 to 7 hours of sunlight every day and damp soil. You will be able to see the first seedlings after six to eight days.
  2. Once your plants have reached a height of roughly 10 to 15 cm you can replant your onions in a bigger container. The new pot should have a diameter of roughly 50 cm and a depth of 40 cm. Harvest your onions approximately 100 to 150 days after planting your seeds when the leaves start to turn yellow.

How to grow onions in water

Onions can also be grown in water. All you will need is a few plastic glasses, some sponges, and an onion set. Start by cutting your sponges to create disks that you will then put inside your glass. Leave some space both at the bottom and at the top of the sponge. Place your bulbs on the top and fill your glass with water so that the sponge is constantly moist. It will take just a few days for your onions to develop a root system. Once this happens, you can move your onion to a pot.

how to grow onions in water
source: youtube.com

How to grow onions from onions

You can also grow onions from old scraps of onions you bought at your local grocery store.

  1. To start, cut your onion bottom, the part with roots, and put it in a glass of water. Use the method we discussed in the previous section and just wait for the roots to grow.
  2. After a few days, you will be able to move your vegetables in a pot and follow the steps we just discussed.

Why do my onions refuse to grow?

So, you planted your onions a few months ago, gave them water, sun, and tons of love, and despite everything, they still refuse to grow. What did you do wrong?
Well, first of all, relax. Despite our best efforts, sometimes our onions simply won’t grow big. But there are a few common reasons why this happens. So let’s analyze them together.

Choosing the right variety

From leaks to red onions, yellow onions, white onions, spring onions, cipolline, and shallots… the list goes on and on. To decide which variety is ideal for you, you need to take into account your tastes as well as your geographical location and current season.

onion variaties
onion variaties


Another common reason why your onions are refusing to grow is that you may have planted them at the wrong time.


You should also make sure to give your onions enough space to grow. If they are too close to each other, they will not have enough nutrients to get bigger. 


As with every plant, onions need the right balance of water in their soil, neither too much nor too little. Finding the exact amount of water is a must for a successful crop.

Harvesting and weeding

Throughout the growing process, make sure to regularly weed your soil to keep your onions healthy. Don’t forget to look for flower bulbs and remove them as soon as you see one to prevent the onion from splitting. Your crop will be ready when the leaves start to die out and turn yellow. Before storing it, you need to dry your onions completely so they can develop their outer skin and last for longer. This process should take about two weeks. Leave your crop in the sun or store it in a dry place if you live in a rainy area.

Frequently Asked Questions

How to grow green onions

You can grow them in a pot, in water or from onions. The only difference is that you can harvest them earlier. You can remove your green onions from the soil once the leaves reach the size of a pencil.

How to grow onions from seed

You can start to plant your seeds late in the winter and then move your crop outside in the spring. Keep the soil moist but not soggy and harvest when the leaves start to turn yellow.