Growing onions from seed is a great way to get large onions to feed your family. While they require more work than planting onion sets, I’ve found that they produce better and offer more variety for your garden.
For the longest time, I thought that the only way to plant onions was with onion sets. I never thought about any other options, that’s just how it was. Then, I started diving into how on earth do these plants reproduce… there has to be a way otherwise we would no longer have onions. Boy, was I surprised to find out that onions actually produce seeds.
Finding this little tidbit of information out opened up the whole world of onion varieties, and I dove right in. Very quickly, I identified that northern states need long day onion varieties. I also identified the traits that I wanted in onions which included storage qualities and large bulb size.
So, I’m going to dive into the basics of planting onions from seed. This includes picking varieties favorable to your environment and starting them inside. Starting onions from seed inside your home is pretty much necessary if you live in a colder climate such as South Dakota. I have seen some people start their onions outdoors in milk jugs or similar containers and it seems to go ok. But I think from a management stand point, this doesn’t allow you to have as much control.
Picking Onion Seed Varieties
The first thing you need to do when picking onion seed varieties is to identify the type of onion that will be best for your environment. There are three types of onion day length varieties to consider.
- Long Day Onions – require 14 and more hours of light. Recommended for northern climates, most often Nebraska and north.
- Intermediate Onions – Require 12 – 14 hours of sunlight.
- Short Day Onions – require 10 hours of sunlight
Within each of these three types, you then can look at the different qualities of the onion varieties and which ones fall into your preferences. Some of these qualities can include how well they do in storage, the size of the bulb, flavor, and other climate factors. Some onions just do particularly well in some climates. I like to look in the reviews section on seed websites to see what others have had good luck with.
The best part about finding onion varieties that do well for you is that eventually, if you want to develop your gardening skills, you can look into saving onion seeds. Just an option! And if not, at least you know what does well in your climate and you can repurchase!
The onion varieties that I have good luck with in the northern United States are long day varieties. My favorites are Yellow of Parma, Ruby Red, Wethersfield Red, White Sweet Spanish, and Utah Yellow Sweet Spanish onion varieties.
Starting Onions from Seed Inside
Starting onions from seed is very similar to starting any other plant from seed inside. There are a few tips and tricks that make the end product turn out better, but the basics still remain true.
A few things in particular about onions to keep in mind is that they are a bulb plant. The end goal is to harvest the bulb. The leaves are very grass-like and end up helping form the layers of the bulb. So, thinking about this, we don’t want dirt to get in-between the layers of leaves as it will end up causing rot in the onion. The other thing about onions is that they tend to have a more shallow root system. So all things considering, it makes sense that onion seed would be started closer to the soil surface. Make sure not to plant your seeds too deeply.
Our goal when starting onions is for the root system and bulb of the onion seedling to develop and become strong. Once your seedlings have sprouted, try to keep their grass-like leaves trimmed to about three to five inches in height. This will cause them to focus more on root development and keep the leaves manageable.
Materials You’ll Need to Start Onion Seed
To start onion seed, you will need seed starting containers & flats, all purpose potting soil, onion seed, scissors, grow light(s), and plant food/seedling fertilizer.
For seed starting containers, I choose to use solo cups with holes drilled in the bottom. This provides a good deal of depth and soil to allow the root systems to become well developed. It is also much cheaper to buy solo cups than purchasing actual seed starting pots.
For potting/seed starting soil, I use the Pro-Mix All-Purpose potting soil. Special seed starting soil can be too fluffy in my opinion. And, all purpose potting soil tends to be cheaper.
Grow lights aren’t necessarily mandatory. If you have a nice large south facing window that receives good light, you can probably use this instead. However, if you’re like me and don’t have that, grow lights are going to be needed. There are many different options available. I just use an LED grow light bulb in a heat lamp frame
Plant food or seedling fertilizer is going to be needed eventually to help your onion seedlings grow strong and healthy. They don’t need a ton of plant food. In fact, you shouldn’t give seedlings more than half the indoor plant rate every two or so weeks or you can end up burning your seedlings and killing them. I use a multi-purpose plant food.
Steps to Start Onions from Seed Inside
It’s best to start onions from seed about 8-10 weeks before your last frost date. You will end up planting them outdoor 2-4 weeks before your last frost date and depending on your snow coverage.
To start onion seed, begin by filling each container/cup with damp all-purpose potting soil leaving about 1/2 inch open at the top. I pre-moisten my potting soil in a large bowl before putting it in my seed starting pots/containers. Next, evenly space onion seeds over the surface of the soil. I tend to just scatter them over the surface evenly. If a few pop up next to each other, that will be fine. Per solo cup, I plant about 50-75 seeds. Just barely cover the seeds with about a 1/4 inch of potting soil and pat down to insure good seed/soil contact…
Place your containers in a seed starting flat so that you can water them from the bottom for the coming weeks. If you have a grow dome that fits your seed starting flat and container of choice, you can place that on to help keep the seeds warm to sprout. For solo cups, I just put some saran wrap over the tops of the cups. Place the seed starting flat with the cups in a warm location (about 75˚F) with the appropriate light. If you’re using a grow light, allow the light to be on for about 12 hours a day, or normal daylight hours. When the seeds have sprouted, you can remove the saran wrap.
Keep the soil damp, but not soaking. After your seeds have sprouted, you can go forward with watering your seedlings in the flat and from the bottom up when the surface of the soil begins to get dry. About every two weeks, you can include plant food when watering at about half of the recommended indoor plant rate.
Remember to trim the leaves regularly (every week to week and a half) to a height of about three inches or so.
Planting Your Onion Seedlings
About 2-4 weeks before your last frost date, you can begin hardening off your onion seedlings by placing them outside for just an hour the first day, 2 hours the second day, and so on until they are adapted to the sun and temperature. This usually takes about a week. Then you should be good to go ahead and plant the seedlings in your garden.
Gently pop the seedlings and potting soil out of the cup/container. Then gently tease the seedlings apart. This actually goes quite well with onions since their roots are fibrous and like long strings.
Plant your onion seedlings in loose, rich soil by making a hole with your finger about a couple inches in depth, placing the roots in the hole. Only plant the seedling to a depth so that the beginning point for the leaves does not go below the top of the soil. Remember, we don’t want soil to get amongst the leaves and the onion to contain soil inside the bulb.
Space your seedlings so that they have about 3 inches on all sides, 6 inches diameter and 3 inches radius.
Keep your seedlings well weeded and water regularly to help your onions grow well. Remember, they have shallow root systems. So when the surface soil is dry, their roots likely will be as well. Some people say to mulch to help with weeds. Some say that mulch can end up causing your onions to be soft at harvest (not desirable). Personally, I don’t mulch at all or if I do, I only apply a light amount that won’t hold onto the water too much.
Will My Onions Produce Flowers the First Year?
Onions are also a biennial plant, meaning that they produce seed during their second year of being planted. So if you plant onions from seed, they shouldn’t flower the first year. If you were to save your onions and re-plant the bulbs in the spring of the second year, they would sprout again. The second year, they would flower and produce seed if the flowers are pollinated. The second year, I would not recommend harvesting and eating the bulbs…
Have you ever planted onions from seed before? Have you had luck with it? Or do you have any questions? Let me know in the comments below!