How to Grow Microgreens Indoors

by Jason Lee • 2/5/2019

Being able to grow microgreens indoors is a luxury. The growing season in the northern climate is only six months. You have one shot at getting it right. Since most vegetables mature in 3 months, if you start too early, frost will kill your seedlings. And if you start too late, frost will kill your harvest.

Luckily, microgreens are easy to grow indoors. You can control the environment to the minutia and have fresh vegetables year round while taking as little as four square foot of space.

In this article, I’m going to give you all you need to know to start growing microgreens indoors as a beginner: including how to light up your microgreens, space considerations, growing containers, vertical growing and even a brief introduction on nutrient film technique.

How to Light Your Microgreens

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LED lighting for growing microgreens

Plants need lights for photosynthesis. Direct sunlight is always the best light source, which provides the entire spectrum at an intensity of 100,000 lux at full daylight. But using sunlight indoors is problematic.

If you live in the northern hemisphere, the sun points south. Therefore, most of the sunlight will originate from south facing windows. If you have north facing windows, you're out of luck. Moreover, the angle of the sunlight changes througout the seasons because of earth's tilt, which means that you have to move the shelving throughout the year in order to maximize the sunlight.

Artificial lighting provides a constant and predictable source of lighting. The options for artifical ligthing are staggering. The top three options for microgreen growers are High Pressure Sodium, Fluorescent, and LEDs. There are pros and cons of each, but it's important to note that none of these lights replicate sunlight.

High pressure sodium are commonly used in streetlights. Ranging from 250 to 400 watts, High Pressure Sodium's spectrum peaks at 600nm, giving a distinctly yellow light. While they are just as efficient as LEDs, HPS emits a lot of heat, which makes it not an ideal choice for home growers.

Flourescent lighting runs cool. It comes in all sizes (T5 to T12) and lengths from 1 ft to 8 ft long. T5's light spectrum has peaks at 450 nm and 600 nm, which corresponds to the spectrum used by plants for photosynthesis. Its low cost and ease to set up makes it ideal for home growers.

Moreover, they are just as efficient as LED lighting. T5 High Output tubes produce 1250 lumens per linear feet, while only consuming 13 watts per linear feet. If you stack up 4 T5HO lighting per square feet of growing space, this translates to about 20,000 lux of brightness, which is 1/5th the lighting intensity of daylight.

Another aspect to consider for grow lights is the color temperature. Fluorescent tubes are sold in either a warm 4500k or a cool 6500k color temperature. Since daylight is 6500k, 6500k is the ideal color temperature for growing indoors.

LED grow lights are also a good option. LED are 20 more efficient than fluorescent lights. Moreover, they are rated to last 50,000 hours of operation, which is 2.5x longer than fluorescent tubes. They generate less heat and are less noisy than fluorescent lights. LED can be tuned to generate multiple different spectrums. It's important to get LEDs that are 5500k or full spectrum. Full spectrum LEDs have minimal green color output, unlike 6500k LEDs.

The cost of LED and florescent lighting are comparable. LED lighting are roughly 1.3 to 1.5 times more expensive than fluorescent, and potentially more cost saving over the long run. I personally use LED lighting for growing microgreens because fluorescent lighting contains mercury, which is harmful to the environment.

Both fluorescent and LED fixtures comes in varieties that are plug in and can be linked together in series, which doesn't require any electrician skill to install. Keep in mind that circuit breakers are rated at 12 - 15 Amps, which is roughly 1000 - 1200 watts of power at 120V.

Space Considerations for Microgreens

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Wire Shelving for microgreens

Since Microgreens are grown vertically, they do not require a lot of space. With an average of 1 to 2 weeks of growth before harvest, microgreens have a relatively high turnaround time, microgreens take up less space per harvest compared to plants grown in your garden.

To accommodate growing microgreens vertically, use a wire shelf. Get a wire shelf that is 4 feet in length. The cheapest wire shelves options are 3 feet in length, which is not sufficient to accomodate most lighting fixtures, which comes in either 2 ft or 4 ft in length. Secure the lighting fixtures to the wire shelves with zip ties. Also designate a shelf space for germination, where non-lit spaces are used for the germination process.

A 4 foot long wire shelf can accomodate 16 square foot of growing space and 4 feet of storage space. Assuming that you eat 1/2 square foot of microgreens a day, a single shelf is enough for a two person household if you limit your microgreen growth to two weeks. It's amazing to think that you can meet all your vegetable nutrition needs with a corner microgreen garden.

Always secure your wire shelving by placing heavy items on the bottom or straps. Wire shelves have a high center of gravity, which can easily topple and harm people if they are not careful.

If you have multiple shelving, make sure to accomodate space for walkways. Allow a minimum of 3 ft wide walkways for safety.

Microgreen Containers

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Shoebox size containers for growing microgreens

We're all familiar with the black plastic seedling trays sold in nurseries. These containers are to be avoided at all costs. They are meant to be disposable, which breaks down and create environmental problems.

The ideal container for home growers is a shoebox sized storage container, 5 - 6 L (5 quarts) plastic boxes with lids. You do not need to drill any drainage holes unless you want to have a buffer to prevent overwatering.

I do not drill holes because the plastic I chose for growing containers are are translucent, allowing me to see how much water is pooling in the bottom. The lids are great if you want to use it as a humidity dome for germination, which saves growing medium used to cover the seeds.

Growing Medium for Microgreens

I have discussed the use of growing medium for microgreens in another article here. To summarize, I use a 10: 1 mixture of peat moss and vermiculite, with fertilizer to a 0.5% Nitrogen by weight for growth longer than two weeks. This growing medium provides nutrients, moisture and aeration, which are crucial for growing microgreens and seedlings alike.

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Microgreen Growing Medium

Time Your Lights

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Light Timer

Plants need sleep. More specifically, plants has a light and dark cycle (circadian rhythm). Plants grows most at night, consuming most of the oxygen and carbohydrates that it produces during the daytime.

The concentration of sugars and carbohydrates are at its highest on end of the light cycle, which you can capitalize on by harvesting at dusk.

You also need to replicate the light and dark cycle indoors. Use a light timer, which is commonly used to control christmas lights.

There are two types of light timers, mechanical and digital. The digital light timer is more expensive and unnessary. You can expand the amount of outlets by using a power bar. Since I grow my microgreens in the basement, I can make up my very own light/dark cycle. Electricity rates are usually cheaper at night, so I start the light cycle at 7 pm and the dark cycle at 7 am.

Watering your microgreens

Plants die from being over-watered and under-watered. Fortunately, you can learn to fine tune your watering faster since microgreens grow to harvest size in 2 weeks.

Novice garderners have a tendency to overwater plants. However, plants are generally resilient to droughts. Overwatering causes plants to drown and slowly suffocate.

This is why having a transparent growing container is very helpful. Plant roots breathe oxygen, which is inhibited by stale water. Perlite and vermiculite can help overwatering by maintaining air pockets, but should not be relied on.

For the first week of growth, it's important to keep the top layer moist. A properly moistened growing medium while planting the microgreens should be sufficient to carry enough water for 4 - 5 days. Using a humidity dome will greatly increase the risk of damping off. Damping off is caused by fungus, whose spores are ubiquitous. Make sure to seed at reccomended rates to prevent spread.

Peat moss have a great indicator for underwatering. The surface of the medium begins to turn a lighter brown color when dry. However, the best way to gauge moisture is by using your finger.

When it begins to feel dry on touch, which is usually after 3 to 4 days since the last watering, it's the perfect indicator to start watering your microgreens. Do not let the growing medium to be completely dry, since dry peat moss repels water.

Harvesting Microgreens

You can harvest the microgreens at any stage after germination. I personally like to harvest microgreens as I consume them. This means I can go through half a container in a day, while leaving the other half for tomorrow.

You can pull off the microgreens or simply cut them with scissors. If you are re-using the growing medium, make sure to remove all traces of the roots, and re-fertilize every 2 months.

Microgreens Nutrient Film Technique

This method of growing microgreens is more advanced. You can see it on display in Disney’s Epcot Living with the Land. Unlike the regular Nutrient Film Technique, the microgreens Nutrient Film tecnhique has the whole channel exposed because of their tighter spacing.

The containers are 20 ft. long and 1ft. wide, angled slightly towards the bottom, where nutrient rich water is continuously cycled in the container at a constant rate of approximately 1L/min.

The plants are kept in place with inert growing medium such as rockwoll. Nutrient film technique doesn't suffer from overwatering issues because the water is re-oxygenated during the end of the cycle.

If you want to set up your own nutrient film system at home, you need pumps, hoses, buckets, aluminum gutters, and a support structures. Do not use PVC pipes not designated for drinking water because this will leech chemicals into the system.

A nutrient film system takes a lot of work to set up and is much more costly to run and maintain. It is also an easy for fungus and bacteria to spread because the water is cycled to every plant. The nutrient film technique is not reccomended for home growers.

On the other hand, the Nutrient film technique is more cost-effective when applied in larger scales. It’s much cleaner than dealing with loose growing medium such as peat moss, and allows you to deliver more nutrients to the plant on demand.

About the Author

Jason Lee

I am the author of this website and owner of growyourmicrogreens.com. I am an hobbyist gardener and a passionate scientist. I was trained as a scientist in the Molecular Genetics program in University of Toronto, where I received my Masters of Science and published a journal article.

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