Do Onions Grow Underground?

on September 25, 2022

Onions are an extremely widely used vegetable that is used in a range of different dishes around the world and is available in pretty much any grocery store. However, if you have never grown onions yourself you may be wondering how they actually grow. Do they grow below the ground or above the ground?

Onion bulbs sit at ground level nestled in the soil in most cases the plants will start as slender green shoots that look similar to chives. As the plants get larger they will come to resemble spring onions before developing bulbs at the base of the shoots which be sitting on the surface of the soil just above the ground.

If you look carefully at the onions from the grocery store you will notice that at the bottom of the onions there is a basal plate where the roots come out of the plant, however, typically by the time you see them in the local supermarket the roots have long-since died back.

The green shoots that you see on growing onion plants come out of the top of the onion at the pointy end which again will have died back by the time you see them in the supermarket.

Are Onions Easy To Grow?

Onions are extremely easy to grow and they generally require very little effort because they have very few pest problems and they are highly tolerant of hot and cold weather conditions. This means that even if you are an inexperienced gardener that you are very likely to be able to produce a good crop of onions.

Additionally, any onions that you produce can be stored for an extended period of time so anything that you grow you will be able to use throughout the year. You may also be surprised to learn that much of the onions in the supermarkets are likely to be anywhere between 3 and 6 months old depending upon the time of year that you are purchasing the product.

Are There Different Types Of Onions?

There are many different types of onions that can be classified based on their appearance, however, from the gardeners’ perspective, they are typically classified based on their physiological behavior when they are growing.

Onions can be divided up into short, medium, and long day-length onions. This classification is based on the amount of daylight that is required to trigger the onions to produce bulbs. Onions are one of the few vegetables where it is advantageous to grow them in the more northern parts of countries where the daylight hours are longer because this allows a wider variety of onions to be grown.

If you live in the tropics because of daylight hours you can only grow short-day-length onions which do not generally store as well as medium and long-day-length onions.

Short-day onions need around 12 hours to trigger the formation of bulbs whereas long-day onions need up to around 16 hours a day of daylight to trigger the formation of bulbs

How To Grow Onions

Onions are extremely easy to grow and can be planted directly into the garden or into a seed tray. We normally recommend that you plant into a seed tray for the reason that it is far easier to control the growing conditions of the seeds which will accelerate the growth ensuring that you get a crop faster.

Additionally, planting a seed tray has the added advantage that it allows you to maximize your space in the garden because you can make 100% sure that you are going to get a viable plant in every space in your garden because it’s already germinated by the time it gets into the garden, so no gaps.

Generally, most gardeners for plants onions in late winter just before the weather is about to start to improve. To sow the seeds fill a seed tray with seed raising mix rather than soil from the garden. The seed tray that you should use should ideally have individual cells because it will be much easier, later on, to transplant seedlings.

Once the soil is in position it is recommended that you plant between 4 and 6 seeds per cell as this will allow you to plant the onions in clumps. This technique, which is referred to by Charles Dowding as multi-sowing, is highly recommended because it has several advantages over sowing the seeds individually.

The first advantage is that a single seed tray will typically hold between 5 and 6 times the number of seedlings which means that this technique is extremely space-efficient. Secondly, the other key advantage is that when you are transplanting the seedlings out into the garden it is much faster because you are planting 4 to 5 seedlings for every planting hole created.

Additionally, because the onions are planted in clumps you can space some further apart which makes it much easier to maintain the garden bed as you can use a dutch hoe to weed rather than having to hand weed which is much more time-consuming.

Once the onions seeds have been planted into the seed tray it should ideally be placed in relatively warm conditions to maximize the growth rate. Onion seeds will typically take between 7 and 14 days to germinate depending upon the specific conditions that the seeds are grown in.

They will typically need to spend a further 4 to 6 weeks in the seed tray before they can be planted out into the garden, however, if there is no space in your garden or the weather conditions haven’t improved significantly there is no harm in leaving them in the seed tray a little bit longer as they usually will not negatively affect the health of the seedling.

Transplanting Onion Seedlings Into The Garden

Ideally, onion seeds should be transplanted in the garden once the weather is starting to improve and ideally any risk of frost has passed though this is not absolutely essential because onions are highly resistant to temperature variations.

When planting the seedlings out into the garden ideally the onions should be put in a warm location that gets at least 6 to 8 hours of sun per day. Ideally, the location should have rich moist and free-draining soil with plenty of nutrients in them.

When you are ready to plant the seedlings out in the garden the clumps should ideally be placed approximately 10 inches apart as this will ensure that the plants are easy to maintain and are there is sufficient space for them to develop properly.

At this point in time it is also important to ensure that you thin out the bunches of onions to ensure that there are no more than 5 seedlings in a clump. The reason for this is that if there are more than 5 seedlings in a clump it will affect the size of the bulbs that are produced.

Once the plants have been placed into the garden there is very little maintenance to do other than ensure that the bed remains weed-free and is water consistently as the plants generally have very few pests.

Harvesting Onions

Onions can be harvested at any stage through their life cycle and you do not have to wait until the bulbs are completely mature. For example, some gardeners produce onions in clumps of up to 10 seeds which allows them to get a harvest of spring onions by picking around half of the plants from the clumps as spring onions. The remainder grow on to form bulbs.

However, if you do want to maximize your yield it is best to allow the onion bulbs to reach full maturity which will typically occur after 3 to 4 months. Typically, once the onions have reached full maturity the green tops will start to brown and wilt, and in some cases fall over completely which is an indication that the onions have reached their maximum size.

If you have a large crop of onions it will be necessary to store them for the winter. To do this start by picking the onions and leaving them in a dry spot to cure for a week or two. This is mainly done to ensure that there is no excess moisture within the onions so that when they are stored they do not get moldy.

To maximize the shelf life of onions which will typically be 6 to 12 months it is best to keep them in a cool dark location that is dry.