How to Grow Arugula Indoors

Arugula is a popular salad green added to salad mixes and less frequently (we need to change this) as a sandwich topping.

We will show you how to grow arugula indoors so you can use it more often.

Arugula has a peppery bite that stands up well to cold cuts and cheese on sandwiches, and a little bit in a salad gives plain bland lettuce some new life.

Below we will show you how to grow arugula indoors.

Arugula is easy to grow indoors, both as a microgreen or to the baby leaf stage. 

Arugula Basics and the Best Varieties

Before we learn how to grow arugula indoors, let’s discuss arugula and the different varieties. 

We will give you some tips on what seed varieties you should look for depending on the temperature of your growing location.

Arugula belongs to the Brassicaceae, or cruciferous family, closely related to broccoli, cauliflower, Brussels sprouts, and mustards.

It is an annual herb called by many names such as roquette, salad rocket, garden rocket, or arugula.

Arugula does best in the cooler temperatures of early spring and fall outside in the garden. However, it does best indoors in rooms with between 60- and 75 degrees.

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When growing arugula microgreens, the temperature is less critical. 

Common Arugula Varieties

The most common arugula seeds go by roquette arugula. This variety does well as a microgreen or in the garden in the spring or fall. 

Roquette Arugula

“Wild” Arugula

Astro Arugula

All varieties of arugula can be grown indoors. However, arugula sold under the “wild” category tends to grow low to the ground making harvest more difficult.

The arugula we use for an example below is Roquette Arugula grown as microgreens. We will also explain how to grow arugula indoors up to baby leaf size.

How to Grow Arugula Indoors

Planting and Watering Trays

Choose a planting tray that has small holes in the bottom. These holes are how the arugula microgreens will eventually get their water.

We do not water over the top of microgreens—only bottom water.

Yes, we mist the soil and seeds with water, but they never see water over the top again.

So, besides a tray with holes in the bottom, you will need a tray without holes large enough to hold the planting tray.

Our Home Microgreens trays are perfect for this. The planting tray evenly waters from the bottom, and the tight-fitting watering tray forces water into the planting tray. 

Also, since the watering tray fits so tightly, it’s impossible to overwater. So extra water will be forced out.

Arugula seed is relatively small and difficult to plant individually. I’m not saying it can’t be done, but I don’t have the patience to space out the seed.

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This isn’t a problem if you’re growing arugula for microgreens. So let’s start there. 

How Much Seed to Use – Microgreens

The photo above is arugula seed in a 1/2 teaspoon. It weighs 1.7 grams, and this is how much seed I use when growing arugula microgreens in our Home Microgreens Trays with a planting area of approximately 38 square inches.

We sell both non-treated roquette arugula seeds and certified organic roquette arugula seeds.

If you are using a tray of different sizes, we have you covered. You can use the microgreen seed density calculator to determine how much seed we recommend for other size planting trays.

Note: Some images below are of the beta Home Microgreens Trays (opaque trays & red lids). The black trays and opaque lids are the new Home Microgreens Trays. Both are similar-sized, but the latter uses much less soil and is more economical.

Microgreen Trays

Sow Arugula Seeds on Soil or Grow Mats?

Arugula seeds can be grown on soil or grow mats.

We prefer soil for several reasons. 

Fill the tray loosely with a good potting mix (soil). 

We use our own soil mix or a coconut coir-based potting mix.

Once the soil is level with the top of the tray, we use a lid, cover, or even our hand to tamp the soil firmly into the tray. We aren’t compacting it hard, only tamping and leveling the soil.

Next, we mist the soil with a spray bottle. 

We do not recommend saturating the whole soil profile. Instead, water so only the upper 1/3 of the soil is moist. There is no sense in adding more water than the seeds need. It can only cause problems. 

Two or three rounds of misting should be enough water.

Use a shaker bottle to spread out the seeds evenly. We find that shaker bottles make spreading tiny dry seeds easier and quicker.

The goal is to spread the seeds evenly. Any seeds that are clumped together should be spread out more. 

In the photo, you can see some seeds touching each other.

This is ok.

What we don’t want are seeds stacked on top of each other. Stacked seeds can lead to mold and disease issues.

Space the seeds as evenly as possible, but don’t let it drive you nuts if a few are touching.

To help settle the seeds into the soil, we again mist the seeds and soil. Again, don’t drench them, only wet the seeds and soil surface.

To Cover & Add Weight or Dome Arugula Microgreen Seeds?

Arugula microgreens tend not to grow tall, especially under intense light. 

For that reason, many people will grow arugula microgreens under a black dome -the darkness and room to stretch causes the plants to grow longer stems. Longer stems make microgreens easier to harvest, and if you happen to sell microgreens, the longer stem adds weight. 

Our Blackout Recommendations for Arugula Microgreens

Most of the time, we recommend using the weighted method for the blackout period.

We think it increases the germination rate and forces the plant to root deeper. 

Deeply rooted plants are easier to grow because they are sturdier. You can miss a watering, and the plants will survive better. 

We put between 2.5 and 5 pounds on smaller trays like the Home Microgreens tray above. For 1020 trays, we put 10 to 15 pounds of weight on a lid covering the seed.

The weight gives better seed-to-soil contact, retains moisture, and forces the plant to push its roots deeper.

If we have an opaque lid or cover, we use a tea towel or other cloth to darken the tray. 

Exceptions to the Rule

However, we do dome arugula microgreen seeds when it is humid and hot in the growing area. We have had trays “burn” up under these conditions with the weighted method.

Larger trays are more susceptible to overheating than the smaller Home Microgreen trays. Still, we dome our arugula and mustards during hot weather (we don’t run AC usually).

How Long Are Arugula Microgreens in the Blackout?

We don’t like to state exact times. 

Many variables exist temperature, moisture, airflow, and even seed genetics. 

Instead, we like to show you examples. 

Then you can look at our examples and your microgreens and better judge. 

Even though we state the number of days in subheadings, take them with a grain of salt. Compare how your microgreens look to the following photos before taking action.

In the example below, the arugula microgreens were in total weighted blackout for 2-days.

You can see they are yellow (except along the back edge where they got some light) and squished. Still, they’re springing up, and if given time, they would have lifted the lid and weight off the tray. 

These arugula microgreens are ready to be placed under the light and watered.

Removing the Dome from Arugula Microgreens

If you grew your arugula under the dome, they would look like the ones below. 

Full disclosure, those are mustard microgreens, but arugula will look the same.

The white isn’t fungus or mold. The white strings are root hairs. 

The root hairs can gather moisture from the humid air under the dome, so they have no reason to force themselves into the soil. 

If you want more examples of root hairs or mold issues, click this link for an article.

If you use grow mats, you’ll see the same thing even if you add weight to the top of the seeds. 

Also, the microgreens take longer to reach this stage when under the dome. However, conditions are perfect for growing, so why rush it? Instead of 2 days, it might take four or 5-days. Either way, when they look like those above, they are ready to go under the lights.

The root hairs will disappear soon after the dome is removed.

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Now is the Time to Water the Arugula Microgreens

Up to this point, we have not watered the microgreens. 

Only wet the soil and seed.

Bottom Watering Arugula Microgreens

Once the microgreens are ready to go under the lights, it is time to water them.

Again, we do not want to water microgreens from the top. This will only cause soil to stick to the microgreens, disrupt the young plants, and increase the chance of disease.

Instead, we add water to the watering tray and slowly place the planting tray with the microgreens into the watering tray.

We start with 1/4-inch of water.

Remember the feeling of the dry microgreen tray. It’s time to water again when it reaches that weight in a couple of days.

You’ll feel the difference between a light dry tray and a heavier watered tray. The coconut coir holds so much water that the difference is very noticeable.

The soil will uptake the water through the holes in the bottom of the planting tray.

How Much Light Do Arugula Microgreens Need?

After growing microgreens for years, we know the factors necessary for good microgreen growth.

Light is not high up on the list. 

Don’t get us wrong, light does matter, and artificial light is the best in a home-growing situation.  But, unfortunately, placing microgreens in windows leaves a lot to be desired.

But almost any LED or fluorescent light will grow microgreens. 

We recommend LED tube lights with a color spectrum of 5,000K.

However, we still grow microgreens under older LED shop lights that are only 20 watts and 4,000K brightness, and the microgreens do just fine.

Our new lights are Barrina LED T5s at 6,500K, and our 2-foot long lights are Barrina LED 24-watt grow lights. 

Both are inexpensive and do a great job growing any microgreen. 

For quick-growing microgreens, the soil you use is more important than the lights. Also, if you’re using grow mats, your fertilizer is more important than the lights. 

As a home microgreen grower, spending a lot of money and doing a lot of research on lights is a wasted effort. However, commercial growers should always research and experiment with all aspects of the grow system to maximize profit.

Arugula Microgreens After 3-days

Interestingly, arugula microgreens are slower than other microgreens to turn green once under the light.

As you see in the photo below, quite a bit of yellow is still on the tray.

At first, I didn’t think the lights weren’t strong enough. But we ran another batch of arugula under the Barrina 6,500K light, and they too, were slow to turn green.

Most other microgreens color up within a few hours.

But not arugula.

So don’t be alarmed if your Arugula microgreens don’t green up after a day under the lights.

You can see that most of the plants are reaching for the lights and are less squished than the day before.

Arugula Microgreens on Day 4

Now the arugula has turned green and is growing and filling in the tray.

You can see that the microgreens are filling in the space, and leaves are growing in size, absorbing the light and turning it into nutrition for the plant and those that eat it.

We believe that planting microgreens too dense is detrimental to the plant and the possible nutritional value of the microgreen. Our seeding density gives room for plants to develop, not fight for space. 

Microgreens fighting for space to grow produce longer stems, not nutritious leaves.

Arugula Microgreens Day 7 & Ready to Harvest

It only took the arugula microgreen seven days to go from a tiny hard seed to flavorful, peppery microgreen.

To harvest these microgreens, cut the stems just above the soil surface with a sharp knife or a pair of stainless steel scissors.

If you wish, you can tip the tray at an angle, so the cut microgreens will fall onto the plate or cutting board.

Many people worry that the soil is messy and will fall out of the tray. 

That isn’t the case using coconut coir-based soil and bottom watering. 

The arugula microgreens are dry and clean. The soil is compact enough to remain in the tray. 

Only harvest what you will use. The arugula will continue to grow in the tray. All you need to do is keep it watered.

We have kept trays of arugula going for over 2-weeks. 

Fresh is always better!

Below are a few more photos of arugula microgreens grown in Home Microgreens trays and a close-up of the mature microgreen leaves. Click the images to expand them for better viewing.

Growing Arugula to Full Size Indoors

A cool thing about arugula is that you can grow it to full or at least baby leave size indoors too!

Below we will discuss how to grow arugula indoors to a larger size than microgreens.

Choosing a Container and Light to Grow Baby Leaf Arugula Indoors

The options for containers are limitless. The container size and shape will be determined by the area where you plan on growing arugula indoors.

You can, of course, grow arugula under artificial light just like you would microgreens.

However, a sunny window will work since the baby leaf arugula doesn’t need to be planted so densely. 

In the summer, even a window with indirect light will work. But during the low light months, you will need a sunny window.

We have grown arugula inside in grow bags. We placed the bags in a southeast-facing window and elevated the bag so that the plants received as much light as possible. 

When the arugula leaned to the light, we rotated the bag.

If you are fancier than we are – we are sure you are – any larger plant pot or planter will work. 

The container only needs to be 4- or 5-inches deep. But a deeper pot will work too.

Setting Up the Arugula Indoor Planter

After you’ve found a location, either under a light or in a bright sunny window area, be sure you have at least 15 inches of room above the pot so the arugula can grow tall and still not get burned by the light.

Add soil to your container. A good potting mix works perfectly.

Then wet the soil.

Arugula Seed Spacing

Sprinkle the seeds onto the soil, trying to space them 1/2- to 3/4-inch apart.

Since arugula seeds are so tiny, this can be difficult but don’t worry. You can thin them to the correct spacing once they have germinated and started to grow.

There is no need to bury the seeds. Instead, use a misting bottle and give them a good spray. The water will set the seeds into the soil. 

You can cover the tray with plastic wrap if you wish to keep moisture around the seeds or mist the soil surface to keep it damp.

After 2 or 3 days, the seeds will start to germinate. When they are 1-inch or so long, you can thin them to the 3/4-inch spacing.

Watering Arugula Plants in Pots

At first, you will have to use a spray bottle to keep the soil damp. 

Eventually, you can water along the sides or bottom water the pot if it isn’t too deep to soak up the water to the depth of the roots.

Harvesting Baby Leaf Arugula

After 4- or 5-weeks, the arugula will be ready for harvest.

Use a pair of scissors and clip off a few of the leaves. 

The plant will continue to grow, and the leaves will get larger.

As long as you don’t cut too far down on the main stem, the arugula will keep growing. 

If the plants start to turn yellow, use an organic liquid fertilizer to help green them back up.

Baby Leaf verse Arugula Microgreens

Is it worth the effort and space to grow baby leaf arugula instead of arugula microgreens? 

That depends on how you use the arugula. 

Not sure what to do with arugula? Well, here are 30+ recipes!

I find it easier to grow arugula microgreens and regrow a tray when I want them again. But some people like the more spicy taste of larger arugula leaves.

For now, we will stick the arugula microgreens. It does take more soil and seed, but they take up less space and are easier to grow and care for than growing larger plants in the house.

We hope you found the article on how to grow arugula indoors helpful. If you want more information, feel free to reach out to me.