How To Start Onions From Seed

Onion plants are a cool weather crop that can be grown either from transplants or seeds. If you want to plant onions from seed, now is the time to do it!

In this post, we will show you how to start onions from seed so that you can have a bumper crop of these tasty vegetables this summer.

onion seedlings in indoor containers
onion seedlings in indoor containers

Why Start Onions From Seed?

Some people buy onion bulb sets (small bulbs) to plant directly into their garden in Spring, and some like to start them from seed. It’s definitely much cheaper to start your own from seed, so that’s what I’m gonna try this year.

I started my seeds over the weekend (Jan 23). They’ll need 8-10 weeks indoors, so find out when the last frost is expected in your area, and then count back the weeks from there to see when you should plant onions as well.

Starting seeds is super easy. (It’s keeping them alive and flourishing once they have been transplanted into the garden that’s the trick!)

How Long Does it Take to Grow Onions From Seed?

One of the most common questions that gardeners have is “how long does it take to grow onions from seed?”

The answer to this question depends on a number of factors, including the type of onion, the climate, and the growing conditions.

In general, it takes about two months for onions to reach maturity.

However, in some cases, it may take up to four months for onions to reach full size.

There are a few things that you can do to help speed up the growth of your onions. One is to plant the seeds in a sunny location. Onions need lots of sunlight in order to grow properly.

Another is to make sure that the soil is moist but not waterlogged. Onions will not grow well if the soil is too dry or too wet.

Finally, be sure to thin out the seedlings so that they have plenty of room to grow. Thinning out seedlings may seem like a difficult task, but it is actually very important for the health of your onion plants.

By following these tips, you can ensure that your onions will reach maturity in a timely manner.

What Month Do You Plant Onion Seeds?

One key to successful gardening is planting at the right time. This ensures that your plants will have the ideal conditions for growth and that they will be ready to harvest at the peak of their flavor.

So, when is the best time to plant onion seeds? In most regions, onions can be planted as early as February or March.

However, it is important to keep an eye on the weather forecast and wait for a period of warm, dry weather before planting. This will give your seedlings the best chance of survival.

Once they are in the ground, onions need very little maintenance and will be ready to harvest in late summer or early fall. With a little planning, you can enjoy fresh, homegrown onions all season long.

Which Type of Onion is Best for Your Garden?

When it comes to onions, there are many different varieties to choose from. But which type is best for your garden? Here are a few things to find the right type:

First, think about the climate in your area. If you live in a warm climate, then you’ll want to choose a variety of onion that can withstand high temperatures.

On the other hand, if you live in a cooler climate, then you’ll want an onion that can tolerate colder temperatures.

Second, think about the soil in your garden. If you have rich, loamy soil, then almost any type of onion will do. However, if your soil is heavy or clay-like, then you’ll want to choose a variety of onion that doesn’t require as much fertilizer.

Finally, think about the pests and diseases that are common in your area. Some varieties of onion are more resistant to pests and diseases than others. If you live in an area with a lot of pests or diseases, then you’ll want to choose an onion that is less likely to be affected by them.

No matter what type of climate you live in or what type of soil you have in your garden, there is a variety of onion that will do well for you.

Onions can be categorized into three onion varieties – short day, long day, and day neutral.

Short Day

Short day onions are a type of onion that is often used in pickling or as an ingredient in salads and other recipes.

They are named for the fact that they need relatively short days in order to form bulbs, and they are typically planted in the fall or winter.

Short day onions tend to be smaller and milder than other types of onions, making them a good choice for dishes where a strong onion flavor is not desired.

Long Day

Long day onions are a type of onion that requires 14 to 16 hours of daylight in order to form bulbs. They are typically planted in early spring and harvested in late summer or early fall.

Long day onions are the most common type of onion grown in the United States, and they are well suited for temperate climates with long summers.

While they can be grown in other regions, they may not form bulbs as large as those grown in areas with longer days.

Long day onions come in a variety of colors, including white, yellow, and red. They have a mild flavor and can be used raw or cooked.

When cooked, their flavor becomes sweeter and more subdued. Long day onions are a versatile ingredient that can be used in a wide range of dishes, from salads and sandwiches to soups and stews.


Day neutral onions are a type of onion that can be harvested at any time during the growing season.

Unlike other types of onions, which have a specific harvest period, day-neutral onions can be harvested whenever they reach the desired size. This makes them ideal for growers who want to extend their onion harvest beyond the traditional growing season.

Day neutral onions are also more tolerant of temperature fluctuations, making them a good choice for growers in more challenging climates.

While they may not be as large or pungent as other types of onions, day-neutral onions are a versatile and reliable option for many growers.

How to Start Onions From Seed

Here’s how to start onions indoors from seed. Really, you would start any other seeds the same way.

Gather Your Materials

First, gather your materials.

seed starting mix and plastic cups plastic tray and seeds
seed starting mix and plastic cups plastic tray and seeds

  • Seed Starting Mix- note: NOT potting soil!!
  • Containers- I’m using Dixie cups, ’cause I have them. You could also use yogurt cups, egg cartons, or a plastic tray. It should be about an inch and a half or so deep.
  • A plastic tray to hold your containers, and to catch the water that will drain out. I use the tray from a package of cookies, or from bakery items.
  • Seeds

Planting the Seeds

Poke holes in the bottom of your container. This will help protect the fragile seedlings from being over-watered. I just used a shish-kabob skewer:

making holes at the bottom of plastic cup
making holes at the bottom of plastic cup

After placing your containers in the tray, fill them with seed starting mix:

pouring seed starting mix in plastic cup
pouring seed starting mix in plastic cup

Next, water the containers until you see the water leaking out of the bottom of them:

pouring water over seed starting mix in plastic cup
pouring water over seed starting mix in plastic cup

The medium should be nice and moist. You may have to let them sit for several minutes to fully absorb the water. You don’t want your seeds to float, but they should definitely be kept moist.

Get your seeds ready! I’m planting Valencia onions (You do need to find out which varieties grow best in your area.):

Valencia onion seeds
Valencia onion seeds

I like to poke a hole to drop my seeds into. They need to be about 1/4″ deep. Then lightly cover the seeds back over.

I started out planting three seeds at a time, but I’m only gonna do two per cup this year. Once they grow a bit, I’ll have to thin these to one plant per cup, and I hate to waste more seeds than I need to, you know?

Once all of my cups are full, I slip the entire tray into a large ziploc bag, leaving it open slightly for ventilation. This creates a mini greenhouse. Then I put it on top of the fridge ( a warm place away from direct light) to allow the seeds to germinate.

Keep the Soil Moist and Wait for Germination

Make sure the soil stays moist by pouring water into the plastic container for the cups to absorb through the drainage holes in the bottom, as needed.

In a few days, I should have some seedlings emerging!

What to Do Once Your Seedlings Start Growing

Some of my onion tops had grown so tall that they were falling over, so I gave them a trim. It’s recommended to trim back to 3-4 inches. They look much better now! Back under the lights they go, about 1 inch from the lights.

cutting onion seedlings
cutting overgrown onion seedlings using a pair of scissors

One of my bulbs burned out though, so I know they aren’t getting enough light. I started hardening them off (getting them used to being outside a little at a time) so hopefully they’ll be ready to go into the garden next week!

Germination Tips

Onion seedlings are super tiny, so all you have to do is sprinkle them over the surface of some wet seed starting mix, cover them with a very fine layer of more seed starting mix, and water with just enough water to wet the top again.

onion seedlings in tray sprinkled with wet seed starting mix
onion seedlings in tray sprinkled with wet seed starting mix

To help the seeds germinate, I either use a salvaged deli tray with a lid, or I put my trays or cups in an open ziploc bag to create a little greenhouse and to help lock the moisture in.

Then I place them on top of my fridge for a few days, checking every day for growth. Once the seedlings emerge, I put them under a shop light, about 2-3 inches from the bulbs.

Here’s my whole setup. I keep them in a tray with a little water for the seedlings to soak up. It’s very important the soil doesn’t dry out, and bottom watering is much better than trying to sprinkle them from above and disturbing the soil and roots.

These are some red onions I started 8 days ago:

8-day old onion seedlings in tray under grow lights
8-day old onion seedlings in tray under grow lights

Hardening Off Your Onion Seedlings

Before you can plant your onion seedlings, you’ll need to “harden them off.” This simply means acclimating the seedlings to life outside of their comfy little indoor container.

To do this, start by placing the seedlings outdoors in a sheltered spot for a few hours each day.

Gradually increase the amount of time they spend outside, and make sure to provide plenty of water. Once the seedlings have acclimated to outdoor conditions, you can transplant them into your garden.

With a little tender loving care, your seedlings will soon become strong and healthy plants, ready to thrive in their new home.

When To Plant Onion Seedlings in the Garden

One of the most common questions that gardeners have is when to plant onion seedlings. The answer to this question depends on a number of factors, including the climate in which you live and the type of onion that you are growing.

In general, onions should be planted in the early spring, as soon as the soil can be worked. If you live in an area with a long growing season, you can plant your onions in late winter or early spring.

However, if you live in an area with a short growing season, it is best to wait until mid-spring to plant your onions. Additionally, it is important to keep in mind that onion seedlings are very sensitive to frost.

As a result, it is best to wait until all danger of frost has passed before planting your onions. With a little planning, you can ensure that your onion seedlings are planted at the ideal time for your location.

Planting Onion Seedlings in the Garden

If you’re new to gardening, you may be wondering how to plant onion seedlings. The process is actually quite simple.

First, choose a sunny spot in your garden and prepare the soil by tilling or digging it to a depth of about 6 inches. Then, create small hills or mounds about 12 inches apart and plant two onion seedlings in each hill. You can also plant in a long row or trench, if thatโ€™s easier for you to cultivate around.

Once the seedlings have sprouted, thin them out so that only the strongest plant remains in each hill (skip this step if you planted in rows). With a little care and patience, you’ll soon be enjoying the delicious taste of your very own home-grown onions.

Caring for Onion Plants

Whether you’re a seasoned gardener or a beginner, here are a few tips on how to care for onion plants.

First, make sure to plant your onions in well-drained soil in an area that receives full sun.

Once the onion plants are established, water them regularly, especially during dry periods. Weeding and fertilizing onion plants with compost, compost tea, or fish emulsion is important for several reasons.

First, onions are heavy feeders and need lots of nutrients to produce large, healthy bulbs. Second, weeds compete with onions for water and nutrients, so keeping the bed free of weeds is essential for good onion growth. You can mulch with straw, if you prefer, to reduce your weeding chores.

Fertilizer helps onion plants to develop strong roots, which are necessary for preventing soil erosion and capturing water during times of drought.

Fertilizing also helps onion plants to develop disease-resistant foliage. When it comes to weeding and fertilizing onion plants, a little bit of prevention can go a long way in ensuring a healthy crop.

When the plants start to brown up and the tops start to fall over, it’s time to harvest the onions.

Harvesting Your Onions

Onions are a cool-weather crop that is typically harvested in the late summer or early fall. They can be harvested by hand or with a garden fork.

For the best results, wait until the tops of the onions have begun to brown and fall over before harvesting. To harvest by hand, simply pull the onion out of the ground. If using a garden fork, be careful not to damage the onion bulbs.

Once the onions are harvested, they can be stored in a cool, dry place for several months, ideally in mesh bags. By following these simple steps, you can enjoy freshly harvested onions all winter long!

Can You Direct Sow Onions in the Garden?

Many gardeners choose to start their onion plants indoors, in order to get a head start on the growing season. And now, with the tips you read above, you know how to do it, too!

However, onions can also be direct sown in the garden in some cases. One advantage of direct seed sowing is that it eliminates the need to transplant the seedlings, which can be a delicate and time-consuming process.

Furthermore, onion seedlings are notoriously finicky, and often do not survive the transplantation process. By direct sowing in the garden, you can ensure that your onion plants get off to a strong start.

In addition, direct savings also reduce the risk of disease, as pathogens are often introduced when transplanting seedlings from one location to another.

For best results, sow onion seeds in well-drained soil in early spring or for winter sowing. The seeds will germinate best if the soil temperature is at least 60 degrees Fahrenheit, so if you have a short growing season and it takes a long time to warm up in the spring, direct sowing might not be the best option for you.

Nevertheless, for many, with a little care and attention, your onions will thrive and provide you with a bountiful storage come summertime.

Final Thoughts

Now that you know how to start onions from seed, itโ€™s time to get started! Follow the simple steps outlined above and you should be well on your way to a bumper crop of delicious onions.

Remember, practice makes perfect so donโ€™t be discouraged if things donโ€™t go perfectly the first time around. With a little bit of patience and some TLC, those onion seeds will turn into healthy plants that will provide you with plenty of fresh onions all season long.

Are you excited to start growing your own onions? Let us know in the comments below!

18 thoughts on “How To Start Onions From Seed”


  2. Girl, my new seeds should all be here tomorrow, so I’m a little behind on a couple of things, but the frost here last year was so wonky that we’re going to wait until April 18 or so before we plant anyway….waiting a little later worked better for us last year so we figured we’d try it again. I don’t have the greenest thumb so it does me good to wait until they don’t need so much nurturing lol ๐Ÿ™‚
    I got a LOT of the books you suggested. I got seed to seed. I can’t wait to dig in and get started this year! Girl, we got rabbits!!! ;D ;D Very excited. We’re trading it for beef! –S

  3. Thanks for the tutorial! I’m starting onions and garlic this week from seeds and garlic bulbits. I’m going to use 2″ paper towel and toilet paper rolls… I will use the zip lock bag though, it’s a great idea!

  4. I’ve started other veggies from seed but for some reason was intimidated by onions. I guess it’s because I always heard about people buying the bulbs so it never crossed my mind that I could grow my own. Thanks for showing how simple it can be!

  5. Have you ever tried germinating your seeds before you put them in the cups? I germinate mine on a wet coffee filter in a plastic bag on top of my fridge. Then after they have sprouted, I plant 1 in each cup. That way you don’t waste any seeds.

    Your post reminded me that I need to get some of my seeds started. I am also going to do some winter sowing this year in milk jugs. I guess I know what I am doing this weekend!

  6. I tried onions from starts that I bought at a local garden center last year and it was a total fail!!! I may try direct sewing this year but I think I’m just going to wait to try again until we have a house that belongs to us so I can put them in a real garden.

  7. The containers you buy cakes and pies in, that have the big dome tops make excellent mini greenhouses. I often use them instead of the zip lock bags.

    I am glad you said on top of the fridge. I always take up the end of the dining room table. Glad you suggested that!!

  8. Love your dixie cup/ziploc combo! I just planted mine a few days ago in yogurt cups and have some sprouts. It’s exciting, isn’t it? I can pretend spring is right around the corner with those sprouts peeking up.

  9. We’re getting ready to start some onions from seed as soon as our seed order arrives. We also do both from seed indoors, then directly sown outdoors later on. Then late in summer, we plant another crop of a variety of longer storage onions that will last us somewhat into the winter. Fortunately, my husband does all the seed-starting, planting, and tending of he gardens; my part is the canning, freezing, cooking, etc! And this summer, I’ve vowed to actually use the dehydrator I bought last last year! I have a small herb garden I’d like to expand on this year, but want to work on drying some of them this year.
    By the way, have you ever grown lemon balm, or know what you can do with it? I tried growing some last year, and boy it was prolific, but I guess I need to learn more about what you can use it for.
    Good luck with your seedlings! Oh, and a friend of mine who is a great gardener told me that if the tops of the onion seedlings are getting too tall before it’s time to transplant them outside, it won’t hurt them to “give them a haircut!”

    • Lucky you, Pam! Sounds like your husband is a good helper. I LOVE lemon balm. My mother-in-law grows it… it smells wonderful! But I’m like you, no idea what it’s good for. Surely something! Sounds like a good Google search topic ๐Ÿ™‚ Yeah, I read that I can cut the tops of the onions if needed, and use the cutting to cook with. Thanks!!

  10. I am thinking of using a flat container to start my onions in and then I read you could pick them out with a spoon and plant in the garden when the time comes…what do you think?

  11. may i suggest using a shallow try and broadcasting the see in that.. then transplant from there.. a big was of soil, cups, and time especially if you want to plant more than just a couple onions.. roots stay shallow for a long time with onions and they do very well in about an inch or so of soil for a couple months

  12. May I suggest trying some direct sown onion seeds, just for kicks? Compared to indoor starts… No question – direct sewn (even my Walla Walla onion seeds!) just grow bigger and better, despite the lack of a headstart. I tried doing starts for a few years, and it ended up being a waste of time for me when the outdoor ones did better – now I get to focus on the heat loving goodies like tomatoes indoors. ๐Ÿ˜€


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