How To Grow Red Mustard Microgreens: 2 Easy Ways

Mustard microgreens are a fun group of plants to grow. They come in various shapes, colors, varying degrees of spiciness, and are easy to grow. 

One of my favorites is Red Garnet Mustard. This variety is an excellent microgreen, but it can be grown to the baby leaf stage in the garden to add bright colors and flavors to any salad.

Red Garnet Mustard microgreens have the same deep burgundy color as the popular Rambo Radish. But unlike radishes, which have a short harvest window, mustards can be grown for a long time and harvested as needed. 

This article will show you how to grow mustard microgreens using two methods. We will let you decide which way is best for you and discuss why we grow them using one method over the other. 

mustard microgreens

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The mustard microgreens shown above were grown under what we now consider sub-standard, or at best, minimal recommended lighting (low-watt 4,000K lights).

The microgreens in the cover photo were grown under our recommended low-price Barrina LED lights  (2-20 watt, 6,500K lights). 

Notice the color difference.

Methods We Use To Grow Mustard Microgreens

The methods we use to grow mustard microgreens are the weighted and dome methods. 

home microgreens sells seeds

FREE Home Microgreens Grow course that teaches you the basics of growing microgreens in your home! There are 12 video lessons (over 120 minutes), downloads, and more written information and tips!

With mustard microgreens, both methods will produce equal results. The reasons to use one over the other will depend on how you care for microgreens and at what growth stage you wish to harvest the mustard microgreens.

Below we discuss how to implement the methods and show you how the mustard microgreens respond.

Both Methods Are Planted This Way

We will publish a more in-depth article on how we prepare trays for planting in the future.

Our online course, fundamental ways to grow microgreens, will be available soon too.

You can also watch our introductory video on the Home page by clicking here.

Choosing A Tray

Microgreen trays, whether using soil or matting, should be as shallow as possible, reusable, sturdy, and consistent in size for the following reasons.

  • Use less soil
  • Easier to harvest from
  • allows more light and airflow to get to plants
  • sturdy trays are easier to handle and last longer
  • Consistent in size, so when you replant, you can use the previous results to modify or systemize any changes.

Choosing A Tray Size

The size tray you use for any variety will depend on how many microgreens you will consume in a timely manner.

We may use a 1010 tray for broccoli for our use, but we could never use a 1010 trays worth of mustard microgreens.

So to keep everything the same and for easier care, we use the Home Microgreen Tray and grow different varieties at the same time. For instance, grow two Home Microgreens trays of broccoli (instead of 1010) and one of mustard to keep watering and care the same for all trays.

Filling The Tray With Soil

Now that the tray is picked out, we fill it with Home Microgreens Potting Mix or a coconut coir-based mix (not pure coir). 

If you’re using a fiber mat, place your mat at the bottom of the tray.

We always use soil. Microgreens grow great in our potting mix without adding fertilizer, as you do with mats.

Fill the tray loosely to the top or slightly below the top of the tray edge. The lower the soil is in the tray, the more difficult it will be to harvest. 

coconut coir as microgreen soil

Level The Soil or Mat

Use the lid of the Home Microgreens Tray to level and slightly compact the soil. Leveling the soil and taking out the divots and low spots reduces the chances seeds will congregate together. 

This should bring the soil level slightly below the edge, making it easier to harvest yet making a bumper to contain the seeds when they’re sown.

For mats, we suggest finding something to level and smooth out the mat, as seeds will also find low spots and roll into them.

Seeds bunched together can lead to mold problems and make for uneven growth.

If you’re not using a Home Microgreens tray, find something that will smooth and slightly compact the soil inside your tray.

Leveling and compacting the soil will make dispersing the seeds evenly across the surface easier.

leveling the soil

Wet The Surface

Use a spray bottle to wet the surface of both the soil or fiber mat. 

A fiber mat will wet straight through; that’s okay. 

However, with soil, don’t saturate the whole soil profile. 

Only wet the soil’s upper third (at the most half). We don’t want too much water in the system at this point. The moist soil will be enough for the seeds to germinate and start rooting. 

Too much moisture increases the chances of mold or damping-off disease during germination and rooting.

wetting beet microgreen seeds

The soil over the seeds is wetted with a spray bottle, ensuring all the added soil is moist.

How Many Red Garnet Mustard Microgreen Seeds To Use

We use 1.8 grams of Red Garnet Mustard seeds with our Home Microgreens trays. That is equal to about 0.05 grams per square inch of planting surface. 

An 8- by 6-inch tray would have 48 square inches of surface area, so you should plant around 2.4 grams (48 X 0.05) of Red Garnet Mustard seed.

We have a handy calculator that can calculate how much seed you need for the most common microgreens. All you need is the dimensions of your planting trays.

For Red Garnet Mustard, use the value for Wasabi Mustard once you enter your tray dimensions. They have the same seeding rate.

The totals from the calculator are perfect for smaller trays. But as you approach the 1020 size, some adjustments may be necessary. 

Click here to visit the Home Microgreens Seed Calculator

Sowing Red Mustard Microgreen Trays

There is no need to pre-soak mustard seeds.

Mustard microgreen seeds are relatively small, so we recommend using a shaker bottle to help spread the seeds. The bottle should have holes around 3/16 inches in diameter. A seed shaker bottle is nothing other than a small spice jar. 

sowing lettuce seeds

The secret is to tip the bottle at a low angle and then tip it more upright as the seeds empty. 

We’ve seen people use it like a Parmesan cheese shaker. Be more gentle and try to spread the seeds slowly. The starter video shows the correct motion.

We start seeding along the outside edges of the tray and work in circles toward the inside. Plan on making at least two trips around the tray. 

Distribute the seeds evenly across the surface. You don’t have to be perfect, but you don’t want clumps of seeds or areas without seeds. 

Tray of Red Garnet Mustard Microgreen Seeds

Below are two trays of mustard microgreen seeds after sowing.

mustard microgreen seeds

You can click the image to expand it for better viewing.

Some of the seeds are touching. This really can’t be helped unless you want to drive yourself nuts. But, there aren’t any clumps with seeds mounding on top of each other. Each quadrant has about the same amount of seeds. That is good enough.

Mist The Seeds

Give the seeds a good misting to settle them into the soil surface and wet the seeds themselves. Not only does the misting wet the seeds, but it also helps make better soil to seed contact. This is especially important if you’re going to use the dome method to germinate the seeds.

Misting helps space out seeds that are touching. The pressure and water dripping off the seeds separate those that are together. 

Here’s where the two methods, weighted and dome methods, diverge. 

Description of the Two Methods for Germinating Mustard Microgreen Seeds

Weighted Method

The weighted method is called so because you will be placing weight on the seeds.

Here’s another reason to have the soil close to the top of the tray. We use the lids that come with the Home Microgreens Tray as a barrier between the soil & seeds and the weight. 

Besides being a barrier, the lid helps hold in moisture.

If you don’t have a Home Microgreens Tray, you can use coroplast (corrugated plastic used for yard signs) cut to fit into your tray as a lid.

The weight can be a big book, a piece of metal, a large rock, or anything really. We use between 2.5- and 5-pounds for a small tray up to 10 or 12 pounds for a 1020 tray. 

soil for microgreens test weighted trays

Two and a half pound weights added to the top of the tray covers. A towel is placed over the trays to exclude light.

Don’t worry about the weight. The plants can handle it. However, for thin stalked plants like mustards or amaranth, we recommend to use 2 or 3 pounds. 

If you’re using fabric matting, we can also use the weighted method, use the same procedure. 

Purpose of the Weight

The weight holds the lid down on the seeds and pushes them into the soil for better contact. As the mustard seed germinates, the weight forces the plant to react and send down the root into the soil for more leverage to push the weight off.

Domed Method

After the seeds have been misted, take another tray of the same size and place it over the planting tray. 

As the name suggested, a dome is placed over the seeds. 

We suggest the top of the dome be at least 1.5-inches high. This gives the plants some room to grow without hitting the top.

With the Home Microgreens Trays, we use the bottom watering tray as the dome and use the lid as a watering tray placeholder so the soil doesn’t fall out of the tray.

home microgreens tray as a black out dome

Two and a half pound weights added to the top of the tray covers. A towel is placed over the trays to exclude light.

Are You Looking For Microgreen Seeds and Supplies?

Home Microgreens online store sells reasonably priced microgreen seed packets with the perfect amount of seed for 5-by-5, 1010, and Home Microgreens trays plus ounce, 1/4-pound, and pound bags.

We also carry our own microgreen soil and fiber mats for the home microgreen grower!

Check Out the Home Microgreens Store

Note: We are not watering the mustard microgreens yet. Only using the lid to keep things cleaner.

A dark dome is preferred, but if it isn’t dark, it’s okay as we will cover them with a towel anyway.

We suggest putting a small weight on top of the dome to keep it in place.

Blackout Period for Mustard Microgreens

The trays should be kept in a warm place (room temperature) and covered with a tea towel or something similar. 

The purpose of the towel is to exclude light and keep the temperatures moderated. 

tea towel used as blackout material

Two and a half pound weights added to the top of the tray covers. A towel is placed over the trays to exclude light.

We call this the Blackout Period.

In the blackout period for mustard microgreens, we do nothing to the trays for at least 72-hours. Don’t touch them. 

Checking the Mustard Microgreen Seeds After 3-days (72-hours)

After 3-days, it’s time to check on the mustard seeds.

Take a peek, but be careful moving them around and looking at them. Chances are they’re not ready to be removed from the blackout.

If the soil or mat appears dry, you can gently remove the lid and mist them. But it’s best to not disturb them unless you’re positive they are dry.

If you see white, don’t panic. Most likely, it’s only root hairs. 

Once you’ve checked and misted them, if necessary, place them back into the blackout for one or two more days.

When they look like the mustard microgreens in the photo below, they are ready to go under lights.

Mustard Microgreens Day 5 – Under Lights and Watering.

mustard microgreens ready for light

According to the photo’s metadata, the Red Garnet Mustard microgreens above have been in the blackout period for 117-hours.

The tray using the weighted method is on the left; the one on the right was under the domed method.

They’re yellow because they have been in the dark.

The white you see, especially on the domed tray, isn’t mold. Those are root hairs. 

You can see that the weighted method forced the plants to push the roots deeper into the soil. Even though they are bent and crunched up, they will straighten up once they are placed under the light.

mustard microgreens out of weighted blackout

Red Garnet Mustard Microgreens just out of a 5-day weighted blackout

red garnet mustard microgreens from domed blackout period

Red Garnet Mustard microgreens just out of a 5-day domed blackout period. The white is not mold, it is root hairs.

Now Is The Time To Water

Put the planting tray of mustard microgreens in a watering tray and give them their first drink. 

Don’t water them from the top. Don’t mist them either. 

Only put water into the watering tray and let the soil soak up the water from the bottom.

If you’re using a fabric mat, we like to raise the planting tray off the bottom of the watering tray (we use broken plastic coat hangers or pencils). We don’t want the water to float the mat off the bottom of the tray.

We add water slightly above the bottom of the elevated planting tray to give the matting a chance to grab a bit of water. 

Roots will eventually grow down through the holes in the planting tray and wick up water. 

If you’re using fabric matting, add some Ocean Solution to the water, as we did in this article. You will see growth about the same as from soil using this organic liquid fertilizer. 

If you’re using the  Home Microgreens Potting mix, you do not need to add fertilizer. You’ll not see an increase in growth. 

Placing the Mustard Microgreens Under Lights

Now is also the time to place the trays of mustard microgreens under lights. In this test, we used inexpensive shop lights from a box store. 

We do not recommend these lights anymore. Yes, they will grow microgreens, but not as well as using lights similar or better than these Barrina T5 LED lights. The important specifications with these lights are the wattage and the color temperature. 

We recommend using lights at a minimum of 20-watts and a color temperature of at least 5,000K. 

The Barrina lights are 20 watts each and 6,500K. 

Grow lights are not necessary to grow microgreens. Lettuce and microgreens with red leaves (such as these Red Garnet Mustard) grow lights might produce more color. 

We like to have our microgreens 4- to 6-inches below the bottom of the light (if you have more powerful lights with more heat. you will have to increase this distance). 

We Didn’t Follow Our Own Advice

Red Garnet mustard shown below were grown only with a single 4,000K and 30-watt light. Plus. it’s four years old. 

So great lights help, but are not necessary to grow  microgreens.

What does this mean?

Use better lights and your mustard microgreens will look better than those shown!

Day Two Under Lights

Here are the same microgreens after two days in the light. They are starting to show a bit of red tinge on their leaves. 

red garnet mustard microgreens after two days under lights

Red Garnet Mustard Microgreens after two days under light. Weighted method tray on the left and domed method on the right.

The mustard microgreens grown under the dome are taller, but the tray on the left grown with weights, have much thicker stems and larger leaves.

But it’s still too early to make any best growing practices decisions.

Red Garnet Mustard Microgreens Day 9 and Day 4 Under Lights

Nine days after planting and 4-days under the lights. Weighted tray on the left, domed tray on the right.

Both trays are looking great 9-days after planting and their 4th day under the lights. There is still a height difference between the two, with the tray grown under the dome remaining taller.

Let’s take a closer look at the leaves. Remember, you can click on any photo to expand the size for better viewing.

mustard microgreens

Red Garnet Mustard Microgreens grown by weighted method on day 9.

mustard microgreens

Red Garnet Mustard microgreens grown using the domed method on day 9.

The images aren’t very similar, but you can see that there isn’t much difference between the leaf size, shape, or color.

So far, the only difference is that the mustard microgreens grown under the dome appear to be taller. 

A Day Can Make A Difference

The photos below are taken a day after the ones above. Making the Red Garnet Mustard microgreens 10-days old.

red garnet mustard microgreens

Red Garnet Mustard Microgreens on Day 10. Weighted method used to grow the tray on the left. The domed method was used to grow the tray on the right.

Top View on Day 10

red garnet mustard microgreens top view after 10 days

Red Garnet Mustard microgreens 10-days after planting. Weighted method on left and domed method on right.

The growth difference is still apparent with the domed method producing a taller and broader canopy of mustard microgreens. 

Also, more true leaves are forming on the mustard microgreens grown using the domed method. 

The domed method also seems to have a darker red color (I know my photos aren’t great – still learning the new camera). But this could be because the leaves are closer to the weak lights. 

We didn’t harvest these microgreens. We waited five more days. 

Harvest Time for Red Garnet Mustard Microgreens – Day 14

We waited until the 14th day to harvest the mustard microgreens. There isn’t a good photo, but the tray grown using the domed method was a bit overgrown and falling over. They should have been harvested on day 12 or 13.

Below is the weighted tray on day 14.

Red Garnet Mustard Microgreens 14-days after planting

Our Take Aways on Growing Mustard Microgreens 

Both the weighted and domed method can be used to grow mustard microgreens. 

There are differences between the two methods. 

You can use the differences to your advantage depending on how soon you want to use the microgreens and your flavor preferences. 

Differences Between the Weighted Method and Domed Method with Mustard Microgreens.

The dome method will grow mustard microgreens that are taller and mature a couple of days sooner than those grown using the weighted method.

True leaves appeared sooner and in more abundance using the domed method. 

mustard microgreens

Here are our recommendations.

If you want to use your microgreens sooner, use the domed method

Those that like the flavor of mustards with true leaves (spicer and bolder) use the domed method.

The weighted method grows mustard microgreens that are more controllable, dense, and uniform.

If you want a longer harvest time (cut the microgreens as you need them from the tray), then the weighted method will give you a longer harvest window. 

We also believe that using the weighted method requires less care and worry than the domed method. The weighted method is pretty much plant and forget about them for 3-days. While with the domed method, there is more chance that the soil will dry out.

Although we didn’t count the seeds, there could be less germination with the domed method because of dryness and less seed to soil contact. 


Both methods can successfully grow Red Garnet Mustard microgreens. We see no reason why other mustard varieties wouldn’t respond in the same ways.

We will continue to grow mustard microgreens using the weighted method because we like the uniform and dense-growing pattern.

But really, it’s a wash and comes down to using the method that you are more comfortable with.

Are You Ready to Give Red Garnet Mustard Microgreen a Try?

Red Garnet Mustard microgreen are beautiful, very flavorful, and fun to grow. 

Click the button below to check out the Red Garnet Mustard seeds in the Home Microgreen Store.


  • Todd

    Todd is the founder of Home Microgreens & the Home Microgreens store. He also writes for several other websites, including MyViewFromTheWoods.com. Todd worked at a large farm market, garden & nursery center for 20 years. Somehow he snuck off to become a geologist and professor before coming back to his senses to write & lecture about microgreens and gardening. When not at the computer, he can be found in the garden, trout stream, or mountain trail with his new Springer Spaniel Caden.

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