Growing Onion Microgreens and Leeks Too!

How to Grow Onion Microgreens and Leeks Too!

Very few people think about onion microgreens as a thing.

But let me tell you, onions and leek microgreens are fantastic additions to almost any food dish. In reality, they are tiny spring onions or green onions. 

Just because onion microgreens are these small thin strands doesn’t mean their flavor and aroma are weak. In fact, we think the taste, and for sure, the smell is more intense!

The best part is no tears.

Chopping up onion microgreens will not make your eyes water. Now, onion and leek microgreens aren’t used as a base to dishes like the mature bulb is. However, they can replace spring onions in any recipe.

Are Onion Microgreens Easy To Grow?

Growing onion microgreens is easy but a bit slow to mature, taking between 15 and 21 days.

A cool thing about onion and leek microgreens is that you can get a second and third cutting from your first planting. Unlike most microgreens, the growth is from the bottom of the stem, not the top. 

The yield will be less on the second cutting, but we think it’s worth keeping them around for another harvest.

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*Note: though we concentrate on onions in this article, the same steps and procedures work great for leeks too!

Because onion microgreens at a little over two weeks to mature, we don’t consider them beginner microgreens. We like to get people off to a quick win.

So if you haven’t grown microgreens before, try the ones in our Six Easiest Microgreens to Grow list. After you’ve grown a few trays of microgreens, then give onions or leeks a try.

That said, if you follow the steps below, you won’t have any problems growing onion microgreens.

How to Grow Onion Microgreens Step-By-Step

We’ll go through all the steps you’ll need to take to grow flavorful trays of onion microgreens. Sometimes issues arise, so we will not only show you those but also how to prevent and cure the problem. 

If you want to skip ahead and any point, you can use the table of contents below to click forward in the article.

What Seed Should You Use?

Because onion greens are so thin, you can grow many of them in a small tray. Therefore, the little seed packets you find in stores don’t contain enough seeds to make purchasing them worthwhile. 

You can buy onion and leek seeds from the Home Microgreens Store. We sell them packaged in the right amount for several-sized trays and by the ounce.

Supplies Needed To Grow Onion Microgreens

Here’s a list of the supplies you’ll need to grow your sunflowers. The list is all-inclusive, including optional items; these will be labeled as such. Nonetheless, using all of these things will improve your success.

The list includes links to articles describing and supporting those items.

Each item’s use will be explained in more detail below.

Pin the photo below to your Pinterest Microgreen Board.

How Many Onion Seeds Will You Need?

The number or amount of seeds you’ll need depends on the size of your planting tray.

Onion seeds are a little susceptible to growing fungus or damping-off disease. For that reason, we suggest spreading the seeds so they aren’t touching each other. In places where seeds bunch up, the fungus is more likely to grow.

In the post linked below, you can calculate the estimated amount using the calculator embedded in the article based on your planting tray dimensions. The calculator is a good start, but feel free to adjust the amount when you plant your second tray.

In the end, it’s best to buy more than you’ll need because once you grow one tray of microgreens, there’s no doubt you’ll want to start another tray.

Ten Easy Steps

Below is a list of the ten steps to growing onion microgreens. For a more detailed explanation and a video of each step, look at Growing Microgreens for the First Time.

Here are the steps using the Home Microgreen Kit. If you don’t have the kit, the photos will show you what supplies you need to grow microgreens. You can click images to expand their size.

Step 1

Add a premium potting mix to the planting tray. A planting tray needs small holes in the bottom so water can be drawn up from below instead of top watering once the greens have germinated.

The soil should be firmly compacted and level just below the top of the tray. Please read this article on why I believe growing in soil is better. 

Fill the tray just below or up to the top of the lip—level and slightly compact the soil. The transparent lid included with the Home Microgreen tray (not the red cover that came with the beta HM tray) works well to level and compact the soil.

Step 2

Use a spray bottle to wet the soil surface until you see a sheen of water. Allow the water to soak into the soil, then spray the surface twice or thrice.

We don’t like to wet all the soil, only the upper layer. We believe this cuts down on the probability of fungus or damping-off disease.

Step 3

The variety of onions we grow and sell is called White Bunching Onions. The Leeks are American Flag Leeks. 

Add your onion seeds to a shaker bottle. A shaker bottle will allow you to spread the seeds more evenly. There are between 10,000 to 12,000 onion seeds in an ounce. That’s between 350 and 400 seeds per gram.

For onions, you want about 30 seeds per square inch. So if your planting tray surface is 37.5 square inches, you’d add 3.0 grams of onion seeds to your shaker bottle. Below is a photo of 3.0 grams of onion microgreen seeds, or about 1 1/4 teaspoons.

Step 4

Now that the soil surface is prepared and the onion seeds are in the shaker bottle, it’s time to sow them.

Start sprinkling seeds onto the soil in concentric circles around the planting tray. It’s helpful to hold your spare hand around the tray so seeds don’t bounce out. Luckily, onion and leek seeds are very irregular, so they stay where they land most of the time.

Spread the seeds as evenly as possible across the surface. You may need to unscrew the top off the sprinkler bottle to get the last few seeds out. Once all the seeds are out of the bottle, use your finger to spread clumps of seeds to areas with fewer seeds.

Don’t worry if the seeds aren’t perfectly spaced. The seeds will grow, and the plants will spread out to fill the voids.

The seeds are hard to see on the soil because of their dark color. You can click the images above to expand their size for better viewing.

Step 5

Now it’s time to prepare the onion seeds for germination. Use the spray bottle again and wet the seeds. Go easy so the seeds don’t fly off the tray. The water will also help settle the seeds into the soil.

The next part of Step 5 is called the Blackout Period.

Place the planting tray inside the watering tray. A watering tray does not have holes and will hold water. Use a similar-size tray, like in the Home Microgreen Kit, or use a larger container.

Place the tray lid on the seeds upside down, yes, upside down, so the cover presses the seeds onto the soil surface. Place a weight on top of the lid.

Don’t worry; the seeds and young plants will be alright. We put 5 pounds of weight on the Home Microgreens trays. That’s right; we put a 5-pound iron weight on top of the lid.

If you’re planting more than one tray of microgreens, you can stack up two or three and place the weight on the upper tray. Put trays with larger seeds on the bottom if there’s a difference in seed size.

Then use a tea towel and cover the tray to keep the light off the seeds.

Most microgreens can be left on the soil surface, but they must be covered to keep them in the dark while they germinate (we’re testing this now to be sure).

Step 6

Don’t do anything for three days. Just let the seeds germinate and grow. The cover will retain enough moisture for the seeds to grow. It’s best not to disturb them while they sprout; it will only break off small radicle roots or slow the germinating process.

Wasn’t that easy? Just do nothing.

Step 7

On day 4, take a look at the seeds. You’ll see that germination has occurred, and the onion seedlings are growing! But they will most likely need to be placed back into the Blackout. Onions grow pretty slowly at this stage. 

Check the soil to see how much moisture it has. If it’s still dark, it’s ok. If the edges are a lighter brown, give the tray a quick spray – not too much – just enough to darken the soil.

The onions should look something like the ones below.

If the tray looks like this, it should return to the blackout. Place the lid, weight, and towel back over the tray and check on them in two more days.

Step 8

On the sixth day, remove the weight and lid and place the tray under an LED light. The onions should look like those below, yellowish and squished for lack of a better term.

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Don’t worry; these onions will turn green and stand upright as soon as they are placed under a light.

Since the tray has been under the cover for a few days, you may notice a bit of white fungus (be sure it’s not root hair). If so, spray the tray with food grade hydrogen peroxide to kill the fungus. Don’t use the peroxide in the brown bottle.

There’s a lot of discussion about what light is best for microgreens. We think it’s best to give them as much light as possible. After all, light is where the plants get their energy to grow. Give them as much as you can, whether it be sunlight, cheap LED lighting, or a special grow light.

Don’t fret over it; do your best with what you have.

We use these lights: Barrina LED T5 integrated lights. They work great!

If the soil surface looks dry, use the spray bottle to wet the surface. But this will be the last time you use the spray bottle.

Step 9

Let the onion microgreens grow and water them from the bottom.

Here’s where the watering tray comes into play. Memorize how the weight of the dry tray feels. You don’t want it drier than when it came out of the blackout. So, judge the tray weight; when it feels that light again, it’s time to water.

Add water to the watering tray, a quarter of an inch works at first. Set the planting tray in the water and allow it to absorb the water from below.

Now, the microgreens in the photos above are basil. But it doesn’t matter what is growing in the tray. Watering them is the same, regardless.

Watering from the bottom keeps the microgreens dry, eliminating the possibility of damping off disease and stopping soil from splashing up on the plants.

This is especially important for onions and leeks. They are susceptible to fungus.

The first time you water, you may have to add more water because the majority of the soil in the tray is dry. Afterward, you won’t need to add as much water.

Every other day check the weight of the tray to see if it needs water. The need will depend on the humidity and amount of air moving across the microgreens.

Step 10

After one day in the lights (Day 7), you can see that the onions have turned green and are more erect.

Most of the seed husks will stay on the onions. It’s ok; they’re edible and add flavor to the microgreens. Same for leek microgreens.

Below are more stages of growth.

It’s day 9 for these onion microgreens.

Day 11 for these onion microgreens. They could be harvested if needed. We recommend waiting a few more days, though.

You can see that onions don’t grow quickly but have steady growth. The tray above could be harvested on day 11. But you’ll get more greens if you wait a few more days.

Harvest Day

Onion microgreens are ready to harvest when the greens growing along the edges of the tray start to lean outward. Similar to the tray shown below. The onions shown below have been growing for 13 days.

These onion microgreens are ready to harvest. They are 4- to 6-inches long and are starting to lean outward along the edges.

To harvest, tip the tray about 45 degrees over a cutting board or a large plate using stainless steel scissors or a very sharp knife and cut the microgreens just 1/2 to 3/4 of an inch above the soil surface.

Try not to disturb the soil. If some soil does spill, it’s okay; use your hands to fluff the cut microgreens; the soil particles will fall to the board or plate, where you can wipe it off.

Only cut what you’re going to use that day. Replace the growing tray under the light and let them grow some more. However, they will need to be cut; see below.

Don’t wash the harvested microgreens now; they will store better if kept dry.

It’s always recommended to wash microgreens before you use them (I don’t if the greens are dry and clean).

Home Microgreens Store

All the supplies and microgreen seeds you need to grow beautiful and nutritious microgreens at home!

Our prices are as competitive as the larger seed sellers. We also have our own soil, microgreen kits, and trays!

A Bit of a Warning

Onion and leek microgreens tend to dry and brown out at the tips. I’m unsure if this is because of the proximity to the lights or a lack of water.

When you see this happening, it’s time to harvest the remaining greens and store them dry in the crisper.

There’s Great News, Though!

The onions and leeks will grow back!

Unlike most microgreens, onions grow from the bottom of the plant, not the tips. As long as you cut them half of an inch or more above the soil surface, they will continue to grow.

You can get two to three more harvests from them, even if the yield is slightly less than the first.

What Do Onion and Leek Microgreens Taste Like?

As can be expected, onion and leek microgreens taste like onions! However, there’s a garlic aftertaste with both, especially if the seed husks are on the microgreens.

Don’t worry; those husks are edible and won’t hurt you or your teeth.

The best part about these microgreens is that chopping them up doesn’t make your eyes water.

Onion Microgreen Nutrition

We don’t think about onions providing nutrition; generally, onions are the base for our foods, one of the first ingredients added to the pan. However, onion microgreens do have nutritional benefits.

Onion & leek microgreens contain Vitamins A, B, C, and E, calcium, iron, zinc, phosphorus, magnesium, potassium, and amino acids to your diet.

Check out the Home Microgreens Nutritional Resource.

How to Use Onion Microgreens

Like most microgreens, onions and leeks can be added to salads. Again, you get the flavor and aroma (especially the aroma) without the tears.

They go great on a wide variety of dishes, including soups and eggs, add them to meatloaves or hamburger meat, and you can also use them as toppings for sandwiches and wraps.

It’s best to chop them up when you add them to your dishes unless you want to use them as a garnish.

Give them a try; you won’t be disappointed.

Let us know your experiences with onion microgreens. We all learn more when people share their trials and successes!