Growing the Perfect Onion Transplant

Growing the Perfect Onion Transplant

An article by Travis Key from Lazy Dog Farm

Our two previous blogs discussed what types of onions (short-day, intermediate-day, long-day) you should plant depending on where you live. We also explained the pros and cons of growing white, red, and yellow onions. In this blog we’ll continue the onion discussion and talk about planting onions from seed to ensure the best results in your backyard garden.

Plant Onion Plants, Not Bulbs 

I’m sure you’ve seen the bags of onion bulbs for sale at your local home improvement store or big box store. And while they can be mighty tempting, I don’t recommend planting these if you want to grow large onions. These conveniently packed bulbs will make an onion, but usually not a very large one. The packaging on these bulbs also fails to mention whether these are short-day, intermediate-day, or long day onions. As such, you might be planting an onion that won’t perform well in your growing zone.

Buying onion plants is a much better option than bulbs. In some regions you’ll find onion plants for sale at local hardware stores or nurseries. They usually have the plants available around the time that you would need to be planting onions in your area. Onion plants are usually sold in a bundle, and you simply stick them in the ground. Just be sure to confirm with the store that these are the right day-length types for your area.

The best option in my opinion is grow your own onion plants. If you already have a seed-starting setup in your greenhouse, garage, or a room in your home, you can grow onion plants for your backyard garden. Onion plants are extremely easy to grow. If you can grow a tomato or pepper plant from seed, you can grow an onion plant. 

Advantages to Growing Your Own Onion Plants

There are many advantages to growing your own onion plants as opposed to buying them. We’ll mention three of those here.

1. You get to pick the varieties.

If you’re buying onion plants at a local store or online, you can only grow the varieties for which those vendors have plants. But if you decide to grow your own onion plants, you can choose whatever varieties you want — assuming they are the right day-length for your area. Many online seed retailers sell onion seeds in affordable packets for just a few seeds or bulk quantities. You don’t need much soil or space to grow a significant amount of onion plants.

2. You have better control of timing for planting.

If you buy plants online, you may not be able to get those plants shipped to you as soon as you need them. As a result, your planting might be delayed a few weeks from your ideal planting time. But if you grow your own onion plants, you can start the seeds whenever you like and ensure the plants are ready as soon as your climate allows for planting.

3. Plants don’t have as much transplant shock.

Whether you buy plants at a local store or online, those plants have been out the ground for at least a couple weeks. And while onion plants are tough and will keep for a while out the ground, this means that they’ll usually take longer to start growing again when you put them in the ground. If you grow your own onion plants, you can take them right from your seed trays and put them in the ground. This means less transplant shock and faster growth once in the ground. 

How to Grow Onion Plants

Growing onion plants is easy. You can grow them in a standard seed starting tray with individual cells, or just scatter seeds in a large pot. The onion plants are easy to thin and separate once they’re ready to plant, so don’t worry about overcrowding them. We’ll often plant 2-3 onion seeds per cell in our seed trays and thin them at planting. This allows us to grow a tremendous amount of onion plants in a small space.

If you’re using trays with individual cells, make a small, 1/4” deep depression in the cells and drop a few onion seeds in each hole. Then lightly cover with more seed starting mix. If you’re using a pot or a planting container without individual cells, just scatter the onion seeds across the entire container, press them into the soil with your hand, and lightly cover with more seed starting mix.

Keep the soil moist, but not oversaturated, throughout the germination process. Onion seeds usually take between 6-10 days to germinate. When they germinate, the green sprout will look like a small arch emerging from the soil. A few days after that, the onion seedling will “flip” out the soil and start looking more like a baby onion plant. Often the seed capsule will remain attached at the top of the onion seedling. You can remove it if you’d like, but it’s perfectly normal and it will eventually fall off the seedling.

Once the onion seedling flips from the soil and starts to grow a little (usually 2 weeks after germination), you’ll want to start feeding these baby plants. We feed ours daily with a small dose of AgroThrive General Purpose Fertilizer, but you could increase the mixing rate and feed them a couple times a week instead. We have found that “microdosing” — feeding plants every day at small concentrations — is extremely effective and makes a strong, healthy onion transplant.

We usually mix 4 oz of AgroThrive General Purpose in a 5-gallon bucket and use that mixture to feed our onion seedlings each time we water. If feeding everyday isn’t practical for your system, you can double that rate and feed a couple times a week. Either way, the biologically active nutrients in AgroThrive General Purpose helps to make a strong root system and strong top on the onion plants. This helps them to hit the ground running when they’re transplanted.

Your onion plants will be ready to transplant when they can be easily pulled from the seed starting mix. This usually takes about 6-8 weeks from the time that the onion seeds germinate, so plan based on your intended in-ground planting date. We do like to occasionally trim the tops on our onion seedlings while they’re growing. This helps toughen the base of the onion plant and makes them easier to plant. Just don’t trim them right before planting as this can stress the plants and result in a high mortality rate at planting.

It’s Your Turn!

Now you’re ready to grow your own onion plants from seed! This will not only save you money as opposed to buying plants, but it will ensure you have the healthiest plants that start growing fast after transplanting. Determine your ideal in-ground planting date, then count back 6-8 weeks. That’s when you’ll need to start your onion seeds. Feed them well based on the recommendations above and you’ll have the best-looking onion plants in the neighborhood!

Thousands of gardeners have been tuning in to The Lazy Dog Farm YouTube channel where Travis covers a variety topics ranging from how to successfully start seedlings to how to make a flavorful hotsauce that packs a punch. Accompanied by his wife Brooklyn and their two boys, the gardens on their 2 acre homestead in southwest Georgia are always filled with a wide variety of vegetables that are enjoyed fresh or preserved for later.


  • Stacey

    The article mentions cutting the tops off the onion seedlings. When should the first cut be made, how much should be cut and how often?

  • Michael E Bacchi

    I love this site – honest and quite useful information it does not get better than that…..

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