How to Grow Lettuce Microgreens: Finding the Correct Seeding Density

Are lettuce microgreens a thing?

I guess they are, as multiple people have reached out to Home Microgreens to ask how much lettuce seed they should use and if we could carry larger packets of lettuce seeds.

Some of the questions about lettuce seeds have come as a miscommunication, too. More on this later in the article.

Going on the adage that if one person asks, at least ten others have the same question, we decided to grow some lettuce microgreens. 

For lettuce microgreens, we recommend using 5- to 6 grams of lettuce seed for a 1010 tray and 10 grams for a 1020 tray.

We recommend using 0.8 to 1.0 grams of lettuce per 1020 tray for baby leaf lettuce.

But before you use those recommendations, see how we came to those conclusions, as it might make a difference in the amount of seed you use.

This article will discuss how we came to the above recommendations. We will also show you how to grow lettuce microgreens and the results of growing lettuce at different seeding densities.

This also includes how much lettuce we harvest and what it costs to grow lettuce microgreens. 

How to Grow Lettuce Microgreens

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We grow lettuce microgreens the same way we grow trays of baby leaf lettuce.

The only two differences are the amount of seed you use and the length of time that the lettuce grows.

Our videos in the How to Grow Lettuce Indoors, and Outredgeous Red Lettuce articles, plus the one presented below, show you the step-by-step process.

We will briefly describe it below the video. 

What You Need to Grow Lettuce Microgreens

The equipment needed is straightforward.

• Planting & Watering trays
• Clear Dome
• Potting Mix
• Spray Bottle or a pressured sprayer to gently wet the potting mix.
• Lettuce Seeds
• LED Shop Light or Grow Light – doesn’t need to be a grow light, but lettuce will have more color. We used a Mars Hydro TSL 2000 LED grow light to cover a 2- by 4-foot area.

Planting Lettuce Microgreens

The process is shown in the video, but here is the gist of it. 

1. Fill your planting tray with potting mix (we’ll call it soil as it’s easier to type), and tamp and smooth the surface. It doesn’t need to be perfectly flat like with microgreens. Lettuce seeds don’t bounce or roll. 
2. Place the planting tray inside the watering tray – don’t add water, though.
3. Wet the upper 1/3 of the soil profile. As with microgreens, the whole soil profile does not need to be saturated. The extra water can only cause problems.
4. Evenly spread the lettuce seeds on the soil. We use a shaker bottle or measuring cup (we like these because of the spout) to reduce the clumping of seeds in the soil. How much to use will be discussed below.
5. Mist the seeds once gently to wet the seeds, then more strongly to settle the seeds onto the soil surface, but not so much that you blast the seed and soil out of the tray. The purpose is to wet the seed, settle it in place, and not saturate the soil.
6. Place the humidity dome over the tray of planted lettuce. The dome will keep humidity in and allow light to reach the seeds—lettuce seeds like humidity. The preferred temperature range is between 60-75 degrees. 
7. We do not use a heat mat, and often the area where we plant lettuce is between 52- and 65 degrees. The lettuce will germinate just fine, maybe slower at lower temperatures. 
8. We set the light on a timer for 15 to 16 hours daily. The distance between the lights and the soil surface will depend on the light source.
9. For our LED shop lights, the distance between the lights and the soil surface is about eight or nine inches.
10. With strong grow lights, 150 watts or more, the distance is between 20 and 22 inches. 
11. We keep the dome over the top of the tray until the lettuce seedlings are 3/4-inch tall.
12. When the dome comes off, we water for the first time, not over the top. We are using the watering tray. We add 2 cups of water to a 1020 tray, a cup to a 1010 tray, and 1/2 cup to our Home Microgreens tray. Pour the water into the watering tray and gently lower the planting tray onto the water. The tray may float; that’s ok; it will settle as it uptakes water. 
13. If the soil surface is dry – it shouldn’t be with the humidity dome, but if the soil is a light brown near the corners or edge, it’s ok to use the spray bottle and mist that area. 
14. Let the lettuce grow under the lights.
15. Water when needed. Test the tray by lifting it with a finger. You will tell as the soil absorbs much water and is quite heavy when moist. When it’s light, it’s time to water.

Are Lettuce Microgreens a Thing?

That is the central question this article set out to answer. 

As the name of this website and business is Home Microgreens, many people have assumed that all of the pre-weighed seed packets I sell are calibrated to grow microgreens.

This isn’t always the case, and there has been miscommunication around the lettuce packets I sell for 1020 trays.

Even though the product description says the amount of seed in the packet is to grow a 1020 tray of baby leaf size lettuce, people mistook it as enough for a 1020 tray of lettuce microgreens. 

Since some people mistook the product to grow lettuce as microgreens, I wonder how many people want to grow lettuce as a microgreen.

I know I didn’t want to. I use baby leaf lettuce as a salad base and add other microgreens to dress up the salad and make it more nutrient-dense.

I assumed that lettuce didn’t have enough nutrients to be worthy of being a microgreen. After all, lettuce seed isn’t inexpensive.

But after having conversations with people, I was assured that many wanted to grow lettuce as a microgreen.

They think lettuce microgreens have more nutrients by weight than baby leaf lettuce.

Lettuce does have health benefits, for sure. But is younger, smaller lettuce better than more mature lettuce?

I’m not sure, but I’m also not going to argue if they want to buy more lettuce seed!

How Much Seed Do You Need to Grow Lettuce Microgreens?

I didn’t know, and I didn’t even really have a clue where to start.

So I did what everyone else does.

I went to the internet.

The top Google response, after ads, said to plant 1 ounce of seed in a 1020 tray.

Below is his quote, so you don’t think this is my recommendation!

Holy crap!

This came from Kevin at Epic Gardening – a huge website.

Now, I admit I misinterpreted his intentions. 

Instead, he misled us, his readers, and Google by having us click a poorly focused title.

In the text, he explains he is planting a mixture of lettuce, brassicas, and other types of seeds.

Kevin that is called mesclun mix, not lettuce microgreens.

Stop naming your articles what they ain’t.

Why Did I Listen? – Or Not Read the Fine Print

So, without digging into his article, I planted a tray of lettuce microgreens at a rate of an ounce per tray.

It was 14 grams in a 1010 tray – the same thing.

Better than the Greens at the Masters!

That tray planted at 14 grams per 1010 was so dense and lush that it looked better than Augusta National’s greens during the Masters’ Tournament!

You can see it in the video. 

But as good as it looked on the outside – I admit, I liked running my hand over it when the lettuce microgreens were young.

The inside of the tray was rotted.

Choose Your Own Lettuce Microgreen Adventure

Before I finished growing that first tray of lettuce microgreens, I could tell there wasn’t a one-size-fits-all approach to lettuce microgreen seed density. 

Along with the super dense tray, I grew the same variety of lettuce as a tray of baby leaf. The first variety is Grand Rapids.

How fast the lettuce grows, how large the leaf size is, and how the size of each lettuce plant is vastly different. The seeding density has everything to do with how lettuce grows. While with regular microgreens, that isn’t the case.

I wouldn’t be able to choose a seeding density based on the microgreens’ appearance.

Group testing is necessary.

A Five Tray Lettuce Microgreen Test

Before the first tray finished, I grew lettuce microgreens at several seeding densities and compared their growth and yield. Later I decided to throw in the cost per ounce of lettuce yield too. 

I did not have enough Grand Rapids lettuce seed left, so I changed to Bronze Mignonette lettuce. One of my favorite lettuces to grow in the garden.

I planted 1010 trays of Bronze Mignonette lettuce with the following densities.

1-gram, 2-grams, 4-grams, 7-grams, and 10-grams. Grew them side-by-side (except the 1-gram as I didn’t have room under the light for five additional trays).

After 20 days, I harvested the trays, weighed the yield, and calculated the seed cost for each tray. I also calculated how much it costs to grow one ounce of lettuce microgreens, considering each tray’s price of soil and seed.

Basically, divide the cost of seed and soil by the ounces of lettuce yielded from that tray. 

Buy Lettuce Seed

We carry many varieties of lettuce seeds for indoor and garden plantings!

See the Varieties

Table Showing the Yield, Cost, and Cost per Yield of Lettuce Microgreens

I’ll make a better table soon, which happens when you change the website code. It messes things up.

Graphing the Lettuce Microgreen Results

Graphing the results gives you a better perspective.

The graph below shows:

• The yield of each tray of lettuce microgreens – Blue line using the left axis.
• The cost of each ounce of lettuce microgreens considering the price of only the seed – Yellow Line using the right axis.
• The cost of each ounce of lettuce microgreens considering the price of only the seed and soil – Redline using the right axis.

Data is based on lettuce seed costing $10 an ounce and $3.00 of soil to fill a 1010 tray. 

What Does the Graph Tell Us About Lettuce Microgreens

So there are a couple of interesting things the data show us. And one thing that doesn’t mean much.

Yellow Line

The yellow line shows that using less lettuce seed on a tray reduces the cost of each ounce of lettuce you harvest.

That’s cool!

But, if you consider the yield per tray (blue line), low seeding densities don’t produce much lettuce.

Blue Line

The blue line is interesting.

It shows that the harvested yield increases when you add more seed up to a point.

Adding more than 7-grams of seed to a 1010 tray doesn’t return you much more lettuce microgreen yield.

Since the slope of the blue line is steeper than the yellow line, up to 7-grams of seed means each ounce of lettuce microgreen is getting cheaper.

But the seed isn’t the only cost.

Red Line

The red line tells the financial store of lettuce microgreens.

It considers the cost of the lettuce seed and the fixed cost of the soil needed to grow the lettuce microgreens.

The once cheaper cost low seeding density per yield now costs more money than the higher cost per yield dense plantings. 

But yet again, there is a point where adding more seed doesn’t return a cheaper yield. 

This coincides with the seeding density of 7-grams per 1010 tray. 

Is 7-grams of Lettuce Seed Perfect for a 1010 Tray?

Not so fast. 

In this experiment, 7-grams of seed on a 1010 tray appears to provide the cheapest yield of lettuce microgreens.

But.

We Need to Consider the Quality of Lettuce Microgreens

At 7-grams, the inside of the tray did have one bad spot and quite a few smaller brown leaves inside the middle of the tray. 

The quality was not excellent.

Trays using less than 7-grams of seed were, for the most part, completely edible with much less picking through the yield to get rid of lower quality lettuce leaves.

Did I Wait Too Long?

I harvested the trays 20-days after planting. 

That may have been too long. The quality of the denser trays might have been better, say in 15-days.

The yield would have been less too. 

Maybe harvesting the denser seeded trays in fewer days would have been the same as allowing the less dense trays to grow more. This would have evened out the costs, making both costs about the same per ounce of yield.

But you could have eaten the denser tray 5-days earlier.

This is Why I’m Leaving It Up To You

I don’t have the time to test each variable and compare the results.

I don’t have the interest either.

It’s baby leaf lettuce for me. I don’t think there is that much nutritional difference between baby leaf and lettuce microgreens to make a difference. 

I’ll grow lettuce to baby leaf, even though it takes 30-days or more but using 1-gram or less per 1020 tray of seed.

I’ll cover those baby lettuce leaves with more nutrient-dense microgreens and enjoy it.

Way Too Many Variables

If you look at the lettuce leaves in the video, you can see they get smaller with increased seeding density and are located in the tray. 

Lettuce leaves in the middle of the tray are much smaller than those on the outside.

So what does that mean for taking the data results from a 1010 tray and applying them to a 1020 tray? Or even to a smaller Home Microgreens tray?

Because of all the variables such as time, tray area, seeding density, perimeter length, light strength, and lettuce varietal differences all play a part in the best (if there is one) and seeding density, I think each person needs to figure this out based on their growing parameters.

But, I will give a baseline recommendation to adjust to your own liking and growing conditions. 

Home Microgreens Recommendations for Growing Lettuce Microgreens

Based on the cost and lettuce quality results, I believe it would be best to use between 5- and 6.5-grams of lettuce seed per 1010 tray.

Or 10-grams on a 1020 tray if you want lettuce microgreens.

Let them grow for around 15 to 18 days.

Home Microgreens Lettuce Microgreen Seeding Density

Lettuce microgreens are planted more densely than those grown to baby leaf size. As a result, microgreen leaves are also smaller than baby leaf. Lettuce microgreens are harvested between 15- to 20 days after planting, while baby leaf lettuce takes closer to 30-days before harvesting.

Lettuce microgreens

• Home Microgreens Tray – 2 grams (wow, seems dense)
• 1010 Tray – 6 grams
• 1020 Tray – 10 to 11 grams

Baby Leaf Lettuce

• Home Microgreens Tray – tray is too small to provide much yield for the time growing.
• 1010 Tray – 0.4 to 0.5-grams
• 1020 tray 0.8 to 1.0-grams

Grow, Observe, Modify

Use the recommendations above and see how it goes. Then, modify your seeding density based on what you observed from your first grow on the next tray.

Let Me Know Your Results

Leave a comment below, or email me, and let me know what you observe from your lettuce plantings.