Growing Onions From Seed

Three white onions tied with each other

Growing onions from onion seeds don't have to be a complicated process at all - it can actually be a very simple and rewarding task that anyone can accomplish with a little bit of time, planning, and effort.

There are many ways to grow onions - using onion sets tends to be more popular as a lot of the hard work has already been done for you. However, there's nothing quite like the feeling you get when you plant onion seeds and are then rewarded with delicious and organic homegrown onions.

Keep reading to learn how to raise this versatile vegetable in your own soil and elevate any dish on your plate.

How to Grow Onions From Seed

Three white onions on a wooden table

Onions are a delectable necessity in kitchens all around the world. Used in many of the recipes you already create in your kitchen, from Indian Curries to Italian pasta dishes, why not grow onions from seed yourself?

In addition to saving a few bucks at the market each week, growing onions from seed can be extremely economical, and there's no denying that growing them yourself always results in far tastier produce than your regular store-bought onions.

To produce the highest quality onion crop, we like to use Lomi to take our trash away and turn it into nutrient-rich dirt - perfect for nurturing those small onion seedlings and more established onion sets.

Lomi by Pela



Lomi allows you to turn food waste into plant-ready nutrients in under 24 hours. Boost your plants while reducing your waste.

Should I Grow Onions From Seed, Seedlings, or "Sets"?

Hand with gloves planting onions

Asking whether a person should grow onions from seed is like asking what kind of car someone should get - there's no right or wrong answer because everyone has their own unique preference!

By using onion seeds to start your onion crop, you have the most variety in what type of onion you can grow and complete control of the nurturing process at every step.

Onions can be a bit sluggish to bloom, so starting from seedlings is a fine choice for anyone who doesn't have the time or space to begin growing their onion seed weeks ahead of planting season. 

The easiest, and least time-consuming way, to grow onions is from "sets," which are dried, immature bulbs from the prior year that are in a state of dormancy. Of course, this isn't always the best option as there is a drop in quality when growing from sets, and you may find the varieties you have to choose from can be very boring and limited.

Really, when it comes down to it, it depends on the amount of room and time you have to dedicate to growing your onions which will usually determine the method you want to storm ahead with.

Which Type of Onion is Best For Your Garden?

Green onion leaves in the garden

The region and climate you live in will determine what kind of onions you will be able to grow. In general, most varieties of onions will need a space with lots of sunshine during the day and nutrient-rich soil that has been mixed with plenty of organic matter to provide all the nutrients these heavy feeders need.

When it comes to sourcing organic compost material for our plants, we love Lomi, as it's the perfect tool for keeping a healthy supply of nutrient-rich dirt at hand for growing delicious fruits and veggies.

Once you have worked out what kind of climate you are dealing with, you can look at what type of onion you can grow in your garden, whether in a container (like a flowerpot of the large trough) or raised beds, or an allotment type set up.

There are three main categories of onions:

  • Short-day onions
  • Long-day onions
  • Neutral-day onion varieties

Most onions begin to form their bulbs once the temperature reaches a certain level and the number of sunlight hours they can get reaches the best level.

Short-day Onions

Onion bulbs grown in transparent plastic cups

Onions that form bulbs with as little as 10 - 12 hours of sunlight per day are considered short-day onions. They grow in mild winter temperatures in zone 7 climates.

Some examples of short-day onions would be Red Burgundy, Texas Supersweet, and White Bermuda.

Long-day Onions

Red onion with sprouts

Onions that form bulbs with 14 - 16 hours of sunlight per day are long-day onions. They grow from late winter to fall require a climate zone of about 6.

Long-onions that grow wonderfully in these environments are Gabriella, Ringmaster, and Sturon onion varieties.

Neutral-day Onions

White onions planted align on a garden

If the onion forms bulbs with 12 - 14 hours of daylight, they are day-neutral onions. Neutral day onions can be grown in most climates, and their season depends on which region you are growing them in.

Red Candy, Red Stockton, and Superstar are great examples of neutral-day onions.

When to Grow Onions

Garden of onions with onion bulb

Knowing when to grow onions is imperative to ensure that your bulbs bloom on time for the harvesting season and also so that they have the perfect environments to produce fantastic bulbs. When you need to plant your onion seeds will depend entirely on the type of onions you have decided to grow.

For growing short-day onions, you will want to begin planting your onion seeds in the fall so that they are ready by May.

Long-day onions are planted in late winter (around February) so that they can be harvested in the late summer.

Neutral day onions typically have the same planting season as short-day and long-day onions, depending on your region.

Select Your Onion Seeds

Different varieties of onion seeds and bulbs

Ready to select your seeds? You will need to ensure that you have the correct type of onion seed that fits your region and climate zone. It's a good idea to do this quick and easy research before purchasing your onion seeds. Otherwise, you may find you have spent money on seeds that won't grow successfully in your climate.

For zone-7 regions, you're going to want short-day onions.

For zone-6 regions, long-day onions are perfect.

Regardless of what zone you live in, you can't really go wrong with neutral-day onions (unless you're in the most southern parts of Texas or Florida, as these regions are typically too hot for any onions to grow).

How to Sow Onion Seeds

Black onion seeds poured from a jar

When growing onions from seed, you're going to want to begin planting your onion seeds about 7-10 weeks before your area's first or last frost date (depending on whether you are planning to plant onions in fall or spring).

One of the best onion growing tips we have for you is to start your onion seeds indoors - this gives you the chance to stretch out your growing season - using transplant trays or pots. By choosing to grow onion seedlings indoors, you also won't have to worry about exactly when the last frost will appear in your region. They will be safe and cozy in your home until it's time to transplant them into your vegetable garden.

If you don't have the space to start onion seeds indoors, they can be planted directly into your vegetable garden, or even into outdoor pots and containers. As long as the soil they will be growing in is free-draining, easy to work (i.e not frozen over), and nutrient-rich, they will be just fine.

But for the purposes of this article, we're going to focus on how to start onion seeds indoors instead of direct outdoor growing or planting onion sets. If you choose to plant yours directly outside, you have to skip the container step and go straight to planting them into the soil.

Step 1: Gather Your Materials

Hand getting black onion seeds

Once you've determined the best time for you to sow onion seeds, which can be influenced by the area you live in, what you're going to need is:

  • Region compatible onion seed
  • Seed-starting mix
  • Container with drainage holes

Any container at least 2 inches deep and has drainage holes will work for germinating your onion seeds. Using biodegradable garden cells is perfect (though DIY plastic containers work just as well if this is what you have at hand).

You can use a store-bought seed-starting mix, but we have found that making your own mix is the most efficient (and economical) way to sow your seeds. Here's a quick recipe for a simple seedling mix:

  • 4 parts peat moss
  • 1 part perlite
  • 1 part vermiculite
  • 2 parts compost (as we said before, we use Lomi for the most micro-rich, nutrient-dense dirt. The best part is that it cuts down your garbage as well!)

Now, if it isn't possible for you to purchase or mix your own seed starting mix, soil mixed with nutrient-rich compost will work just as well, as long as it is free-draining.

Step 2: Prepare The Containers

Garden pots and tools with a sack of fertilizer

The first thing you're going to do is fill your containers with your chosen seeding starting mix or compost/soil mix.

Compress the mix into the containers, but you don't want to compress the chosen mix too tightly - this can impact how easily it drains and also suffocate the shallow roots of your onions. A little light pressure is enough when compressing down your mix.

Then place the container on top of a thin layer of water for about an hour. This could be as simple as letting them stand on a dinner dish that has water resting on it. This is so that the soil moistens from the bottom up and doesn't become too soggy for your onion seeds.

Step 3: Planting The Seeds

Handing planting seeds to garden pots

When you are ready to start planting onions seeds, make small indents in the soil mix with your finger (about 1 quarter-inch deep). Then, place a few seeds in the holes and cover them with a light dusting of your chosen seeding mix. Try not to place too many seeds in each hole, or you will have to thin a lot of your seedlings as they begin to grow.

It won't be necessary to press the mix down again unless you are planting them outdoors, where a little press down will help protect more of your seeds from roaming birds, especially if you are planting them in the early spring and the birds are coming out of a very food-low season. After that, you're ready to go!

Caring Tips As Your Onion Seeds Germinate

Germinating red onion bulbs

Cover your container with a plastic dome and keep them at a temperature of about 72 degrees Fahrenheit. This plastic dome can be as simple as using the cut-off end of a plastic drinks bottle, or you can purchase plastic domes from your local garden store that have been made for seed germination.

These domes act like mini-greenhouses, trapping the heat inside and helping your onion seedlings grow faster. Be careful, though. If your seedlings have lots of heat but not enough sunlight, they can become leggy - which basically means your onion seedlings will grow very tall and skinny in search of sunlight, making them weak.

To combat this, if you are growing them during months when there is very little sunlight, you can purchase grow lights that simulate sunlight and stop your onion seedlings from getting leggy. Having your onion seedling containers in a south-facing spot means your seedlings will have more sun exposure as well. However, If you can't stretch to a grow light and you don't have a suitable south-facing spot, you may need to hold off planting onion seeds until you have enough sunlight during the day.

After about a week of germination, you should be able to see little onion seedlings sprouting through the soil. Onions seeds sprout faster or slower depending on how warm their environment is - another reason to use plastic domes. Once the onion seedlings have reached about an inch in height, you can take the cover off.

After that, keep them in daylight for around 10 hours if they are short-day onion types and 12 hours if they're long-day onion types. Keep the soil moist by watering regularly (be sure not to overwater!) so that the onion seedling produces bulbs.

Transplanting Onion Seedlings To Your Vegetable Garden

Red onion bulb roots pulled out from the soil

Once planting season arrives, usually just before the last frost date, if you are planting in the early spring, it's time to transplant onion seedlings from their safe space in your home to your garden. You will need to harden your onion plants off before they can be planted in their final place.

Hardening off will require a couple of weeks of your time where you take your onion seedlings outside for an hour a day, to begin with, stretching out until you can leave them out all day and night. This gives them the opportunity to acclimatize to their outdoor environment and increases the chances of successful growth after they have been transplanted into your garden.

In all honesty, this is the most time-consuming part of growing onions from seed when you are starting onions indoors. Depending on how many containers of growing onions you have, you may need a little help bringing them outside and back in, or you could spend all day carrying your onion plants from one place to another.

You will also need to make sure you will be planting them in a place where they'll get the maximum amount of sun.

Step 1: Find the Right Potting Soil

Garden pots with soil aligned horizontally

Make sure your soil is loose, moist, and full of nutrients. You can find many brands of potting soil for sale in your local gardening stores, but they can prove to be very expensive if you need a lot. The best way to achieve a good quality potting soil that won't break the bank is by mixing homemade compost into your garden's soil.

Step 2: Remove the Seedlings From Their Container

White Onions on Soil

Transplanting onion seedlings can be a little tricky since they are very delicate at this stage of growth and they can be susceptible to shock if you don't handle them carefully. Still, it's nothing to be intimidated by. If you're using plastic garden cells, you can get the onion seedlings out by carefully pulling the soil away from the sides of the container and gently squeezing them from the bottom.

If you are using biodegradable growing containers, these can be planted directly into the soil as long as you give the bottom a good nip with some scissors to give your onion seedlings extra room to push through their roots. This method is an excellent choice as it removes any chance of damaging the onion plants roots.

If you have used non-biodegradable pots when planting onion seeds, you will need to remove your growing onions from these pots before you plant them in your garden.

Once you have removed the seedlings from their pots, you will need to very carefully run your fingers around the roots to remove excess seedling mix before you plant them into your garden.

Step 3: Putting The Seedlings Into The Ground

Green onion leaves in a garden

You've put in so much effort growing onions from seed, but we're finally on the home stretch, and this is one of the last steps that requires patience and a careful touch.

Once your onion transplants have been removed from their pots, you need to dig out 2-3 inch deep holes in your soil about 4 inches apart to give your growing onions room for their bulbs.

Now it's time to plant onions! Put your onion plants in your pre-dug holes and then cover them with loose soil. Be sure not to pat or press down too hard when topping the soil off, as this can strangle the roots and cause them to dry out.

Step 4: Caring for Your Onions

Red and white onions harvested on a basket

You should care for your onion crops just like you would any other garden plant: water regularly (but not too much, we don't want soggy soil that can lead to a rotting onion bulb) and wait. Adding half an inch of fresh, organic compost monthly will ensure that your onions get all the nutrients they need and help you successfully grow onions.

Although this step is completely optional, we highly recommend it. Onions are very heavy feeders, and if you are hoping to harvest onions with large bulbs, they will need a lot of fertilizer, and nutrient-rich compost is a cheap and eco-friendly way to give them this.

You will know your onions are ready when your onion tops begin to flop over. At this stage, you will need to stop watering them entirely. Choose a nice, dry day to harvest them. You can take a bite out of them fresh from the ground, but we don't recommend that. Instead, try curing them!

How to Cure Onions

Red onions hanged on a wood

Think of the onions you purchase at the supermarket. Can you remember that dry, crusty peel around the onions that you buy? Well, those are onions that have been cured. Curing onion bulbs is the reason that they have such a long shelf life. By creating that protective layer around the inner parts of the onion, you can extend your onions lifespan by weeks or even months.

Meaning, you could grow your onions in the spring and still have plenty to feed you all winter. This process isn't entirely necessary, but we recommend it if you're not using your onions immediately or planting onions in large amounts. We'd also like to emphasize that curing your onions is extremely easy to do and a great option if you are growing onions from seed as you may have more onion plants than you first anticipated.

Curing Your Onions

Red onion bulbs

When curing onions, your choice of storage spot is one of the most important decisions you will have to make. We want the spot we keep them in to be nice and warm, although you will want to keep them out of direct sunlight as this can actually scorch your homegrown onions from seed.

You'll need your chosen storage area also to have good air circulation. Stuffy, humid warmth can invite fungus and rot into your onions. Which will inevitably make all of your hard work mean nothing when you are left with nothing more than a bunch of rotten and inedible onions.

A shed or basement is an excellent curing area, but if you don't have access to these kinds of spaces, a spot on your outdoor deck can be perfect as long as it's covered and out of direct sunlight. Your ideal onion curing temperature is somewhere between 75 and 85 degrees Fahrenheit.

Two Curing Process Options

There are two different ways that are commonly used when curing onions, Wire Hanging or Window Screens. Both bare relatively simple processes, but your space and the size of your onion harvest will determine which method you opt for. In fact, if your onion harvest is very large, you may decide you use both methods to maximize the number of onions you can cure at one time.

Wire Hanging

Wire hanging red and white onions

For this method, you will need to source a fencing wire. Luckily, it's a very cheap material and usually readily available at many hardware stores. We recommend not using chicken wire for this method as the wire isn't strong enough to support large onion bulbs and the holes aren't big enough for threading your onion stalks.

You can get really fancy with your wire hanging and craft a frame to hold your fencing wire nice and taught. This also increases your options for placement as you can easily rest it up against a wall. However, if you just use the fencing wire alone, you will need somewhere for it to be stationed while maintaining good airflow.

Talking about airflow, you will need to make sure that each onion bulb is given plenty of space from the others. You will reduce that all-important air circulation if you thread your onions too close together.

Window Screening

White onions placed on a window screen

This method is great if you have an old window screen lying about and also isn't half as fiddly as the wire hanging process as there is no onion threading involved. 

You will need to have some setup that allows you to lie the window screen on its side while not restricting any of its airflows.

Once you have a good and stable setup, all you need to do is rest your onions on the screen and let them dry in their own time. Just like with the wire hanging method you need to make sure you have enough space around each onion to keep that all-important circulation freely flowing.

How Long Does it Take to Cure Onions?

Lined up onion bulbs placed on a wood

It will depend entirely on your humidity, temperature, and the type of onion you have grown. If you experience higher levels of humidity your curing period will be a lot longer than if your humidity levels are on the lower side.

It can take anywhere from a few weeks to a few months for your onions to fully cure. You will need to keep a close eye on your onions as they cure, removing damaged or rotting bulbs as you notice them, so they don't infect other bulbs. Your onion bulbs will also need to be fully cured before you move them to your long-term storage area.

How Do I Know My Onions are Cured?

Red onion on black background

When that crispy paper-like layer forms around the onion and the stem of the onion is completely dry, brown, and withered, your onions are most likely fully cured. To properly ensure the process is finished, snip the neck of the top part of one of the onions to see if there are any green parts left. If there isn't a hint of green, your onions are cured. Snip the leaves and roots off, and your onions are ready for storage.

Why Planting Seeds is Better Than Planting Sets

Planting sets grow onions much faster and require much less effort, so why should you even bother with the germination process? There are many reasons why you'd want to go the extra mile and plant seeds. Here are just some of those reasons:

You Have A Wider Choice Of Onion Varieties

Hand with gloves planting seed to the soil

If you go to the gardening center to buy onion sets, you're most likely going to be limited to options. Most providers don't offer that many varieties of onion sets as opposed to the numerous types of onion seeds you can get online. Remember, if you go for onion sets, you're likely limited to three common varieties; if you go for seeds, you can get more types than you can read.

By going for onion seeds, you can plant more exotic and heritage types. The only downside to heirloom onions is they may be a little bit more picking when it comes to growing and curing environments, so you will have to do a good bit of research to make sure your fancy onions will grow well in your region.

Onions From Seeds Are Cheaper

Black onion seeds

Let's talk about cost-efficiency. Onion sets are usually a bit more expensive than seeds. Onions aren't known for being expensive delicacies, so why pay a bit extra? Sure, they're easier to grow, but you may only get about three different varieties to choose from, and these varieties are already available at your local supermarket.

Onions From Seed May Be Better Quality

Onion flower stalks

Bigger is better, right? Not in the case of sets. If the onion sets are too big, they won't grow well and risk bolting. When an onion bolts, they begin to create flower stalks. These flower stalks redirect the nutrients from the growth of the onion bulb to the plant trying to reproduce. Not what we want when growing onions from seed.

Seed growers spend a lot of time making sure their seeds are of the best quality, whereas a lot of generic onion sets are grown in large quantities with not much thought to the quality of onions they will produce.

By growing onions from seed, you have control over every step of the growing process, and you can make sure they receive the perfect amount of nutrients for the tastiest onions.

You also give yourself the option of starting seeds indoors. With onion sets, you are more likely to plant them directly into your vegetable garden bed.

How Late in the Year Can You Plant Onions

Hand planting young onion bulbs on the soil

Planting your onions as early as possible provides the highest quality, largest onions. Planting them a little later yields slightly smaller but still completely usable onions.

So this begs the question: how late is too late?

Once again, we recommend planting onion seeds 7-10 weeks before your last frost date if you are planting long-day onions and 7-10 weeks before your first frost day if you are planting short-day onions.

The latest possible time you can plant onion seeds so that the bulb onion is roughly 1 month before your final/first frost date. It's not ideal, and your yield won't be quite as fruitful, but it can definitely be done in a pinch.

Ready to Grow Your Own Onions?

Green onion leaves in a garden

Did you know that there are hundreds of different kinds of onion varieties for you to try?

If you've been buying the same three colors of onion at the store all your life, this may come as a surprise to you because you've barely even scratched the surface. 

So maybe it's time to start digging. Whether you're a suburban gardener looking for something to plant in the upcoming planting season or a chef wanting to take their culinary art to another level, growing onions from seed is an amazing experience that everyone should try at least once in their life!

And now, hopefully, this article clears up any misconceptions about growing onions from seed being a daunting task and shows that it truly is a simple process that anyone can do.