How Much Light Do Microgreens Need to Grow Better?

Microgreens are not only packed with nutrients, but they are reasonably easy to grow in a matter of weeks! But if you live somewhere where you don’t get a lot of sunlight, artificial light can help supplement your plants’ growth. But how much light will your microgreens need? 

As a general rule, 12-18 hours of artificial light is sufficient for microgreens’ best growth. Under natural light, it is best to give them 5-8 hours of sunlight under shade to prevent scorching. However, different seeds will have varying growth rates even if they receive the same amount of light.

Below, I discuss more on microgreen’s light needs, recommended grow lights, and additional care tips for the plant’s best development:

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Do Microgreens Need 24-hours Light Exposure to Grow?

It’s a common misconception to think that microgreens need light 24/7. Like all living things, they need darkness to rest and develop well. They won’t grow faster just because they have unlimited light. It doesn’t work that way. It mainly depends on whether the seeds you’ve chosen are the fast or slow-growing variety.

I have come across a few claims that say doing this 24-hour light method a day before harvesting is beneficial to boost yield. However, there doesn’t seem to be a significant change between that and normal light durations. As a general rule of thumb, never expose microgreens to light for 24 hours. It will likely cause leaf distortion with delicate plants and may affect the flavor profile.

As mentioned in the introduction, microgreens only need 5-6 hours of direct sunlight or 8 hours of indirect sunlight daily. But when it comes to artificial light, it’s often 12-18 hours depending on the light intensity coming from the bulb. More on that in the next section.

But before giving them light, some microgreens require a ‘blackout period’ during their initial germination. This means letting the seeds sprout in complete darkness before exposing them to light. However, it’s essential to know that not all microgreens require this. Check whether your seeds need it according to the packets they come in, or look them up real quick on Google. 

Adding weight on top of the cover during the blackout period is also recommended. It ensures that the seeds are constantly pressed into moist soil to encourage root growth. Alternatively, you can push the seeds down during planting and apply a thin layer of potting mix on top. However, the downside is you might end up with a messy harvest.

Here are a few common microgreens and their blackout periods for your perusal:

Microgreens	Blackout Period
Arugula	4-5 days
Broccoli	4 days
Cabbage	3-5 days
Kale	4 days
Mustard greens	3-4 days
Radish	3-4 days
Sunflower	3-4 days
Cauliflower	4-6 days
Kohlrabi	3-4 days
Amaranth	4-5 days
Basil	4-5 days
Carrot	4-5 days
Cilantro	6 days
Scallion	Not needed
Swiss chard	4-5 days

Why do microgreens need darkness to grow?

In the darkness, microgreen seeds will stretch to try and reach for sunlight, resulting in long, thin stems. It also keeps humidity and moisture inside to stimulate germination. Not only will this help increase overall yield, but the taller stem height makes it easier to harvest them. However, it’s worth noting that not all microgreens require darkness in their initial growth. But they all do need at least 6 hours of dark daily to rest.

Can microgreens grow in low light?

Low light is acceptable, but microgreens will not grow as quickly or be as flavorful. This is even more prominent for slow-growing varieties such as Basil and Amaranth. Provide plenty of natural or artificial light where possible to encourage fuller microgreen growth. Proper light levels can also help prevent mold on your microgreens.

Can microgreens grow in the dark?

Microgreens will not grow in complete darkness because they still need sunlight for photosynthesis, which helps them to grow and build their flavor profile. However, they generally still need a dark period during germination (not for all seeds) and after exposure to light (for all seeds). The latter allows them to rest after a day of photosynthesizing.

Can I grow microgreens under shade?

It’s better to grow microgreens under a shade with indirect sunlight to prevent the tender leaves from scorching. But ensure to rotate the tray to get even light exposure and prevent leggy growth.

What Grow Lights Make Microgreens Grow Better?

Many different types of grow lights are available on the market these days. And each light has a range of light intensity that will influence your microgreens’ growth and flavor profile. But where do you start?

Let’s quickly run through the common grow lights you see out there:

• Incandescent.

You’re unlikely to see these around anymore because it’s simply not as cost-effective as LEDs and fluorescent grow lights. It puts out too much heat, doesn’t last as long, and uses too much energy to produce light. Their light spectrum is also limited, emitting more red light, which is more helpful in encouraging blooms and fruits. The only good thing about them is that they are cheap.

• HID (High-Intensity Discharge).

These grow lights are more suited for large-scale commercial productions because they are huge and must be hung overhead. The distance is crucial because they give out a lot of heat. Not only are they expensive, but they also are not worth using for home-grown plants. Although, they do emit broad light spectrums, which is helpful for the plants’ growth.

• Fluorescent.

Compared to the previous two grow lights, these take less energy to produce more light. They also produce broad light spectrums but lack selections in a more specific range, such as red light only. They are also relatively cheaper than LED lights but do not last as long.

• LED (Light Emitting Diodes).

These are the grow lights you’ll see dominating the shelves in the store. Not only are they better than the previous lights in terms of energy efficiency, less heat produced, and diverse selections in terms of type and light spectrum, but they are also long-lasting. The only backdraw is that they can be a bit pricey, but as a long-term investment, it’s certainly worth it.

With that in mind, I recommend going for the LED grow lights every time, whether for growing microgreens or other plants. 

Light Spectrum & Color Temperatures for Grow Lights

But wait! You’re confused about light spectrums? Ok, let me break this down for you:

Imagine the light spectrum as a rainbow. Each color on the rainbow has its own energy. Plants primarily make use of red (for fruit and flower growth) and blue color (for foliage growth) as energy for photosynthesis. 

So a ‘broad light spectrum’ often refers to a mixture of colors that the grow lights emits, producing bright white light like the sun. These usually are in the 4500-6500k range of color temperature. While a ‘narrow light spectrum’ is a specific range of light, like red or blue light in the 2200-4000k range.

Luckily, LED lights have all that and, as I mentioned, come in varying sizes and prices to suit your microgreen needs. They can be used as supplemental lighting on top of giving them natural sunlight or be the main light source for your plants.

Therefore, LED lights with bright white color in the range of 4500-6500k color temperature are the best grow lights for microgreens growth. Anything lower on the light spectrum may be suitable for fast-growing seed varieties but not for slow-growing ones. But you’re welcome to start with that before venturing deeper into the microgardening life. When all else fails, good ol’ sunlight will get your greens growing.

Helpful tip: Place the grow lights 4-6 inches away from the microgreens. Adjust the height higher as they grow taller. You can also use an automatic timer to switch the lights on rather than waking up at ungodly hours to set it.

What range of light spectrum helps microgreens grow?

Microgreens grow best at 400-700nm on the light spectrum because this is where the red, green, and blue light is. All plants primarily use this range for photosynthesis, also known as PAR, i.e., Photosynthetically Active Radiation. It’s worth noting that different light spectrums have varied effects on the growth of microgreens and plants in general. For example, blue light promotes foliage growth while red light results in bigger blooms and fruits.

Do microgreens need 6500k to grow?

Microgreens don’t necessarily require 6500k in color temperature to grow. However, it promotes better compact growth and plentiful yield as a result. This is because 6500k is the sun’s average light intensity, which benefits most plants’ development. But generally, microgreens will develop well above 4500k.

What is the best-LED light type for microgreens?

An LED strip grow light is the best type for growing microgreens, preferably with T5 bulbs. These are suitable for focusing as much light as possible on the microgreens, especially in a small-scale set-up. The ‘T’ refers to the bulb’s tubular size, in which T5 is about 5/8ths the size of a T8 bulb, which is 1 diameter. T8 bulbs can also be used but require more energy to produce light.

What Do Microgreens Need to Develop Well?

Now you know all about microgreens’ light needs and the best type for their growth. However, that doesn’t mean you should ignore the rest of their basic needs. Here’s an overview of that:

• Seeds: Only use organic and non-treated seed varieties. 
• Soil: Sterilized, soilless potting mix (peat or coir based) with no added fertilizers and aerating materials like perlite or vermiculite.
• Water:
  • Use filtered or distilled water to bottom-water the tray before planting. This helps to dampen the growing media so the seeds will stick better to it.
  • Mist the seeds after planting twice daily to keep the potting mix damp but not soggy. Stop misting once sprouts appear.
  • Bottom-water as needed when the soil’s surface looks/feels dry. Drain any excess moisture to prevent mold growth.
• Temperature: 68 to 72°F.
• Humidity: Less than 50%.
• Fertilization: Not necessary.

Before we wrap things up, here are some helpful tips for growing your microgreens:

• Never use seeds from nightshade plants like tomatoes, eggplants, peppers, and potatoes for growing microgreens. This is because they have a substance called alkaloids which is toxic for human consumption. 
• Source microgreen seeds from reputable sources. Two popular places people tend to order from are True Leaf Market and Johnny’s Seeds.
• Know your microgreen seeds. Depending on the variety, they may be fast or slow-growing, require presoaking before planting, needs certain temperatures to germinate, or don’t need a blackout period. This way, you avoid certain grievances like why your seeds aren’t growing or why it’s taking so long.
• Never use garden soil to grow microgreens. This is to prevent mold and pathogens from contaminating your plants. If you have no choice, it’s best to sterilize it first. You can read this soil sterilization article to find out more about it.
• Use new potting soil each time you plant microgreens. It is somewhat alright to reuse them. However, this will increase the chances of diseases, so it’s best to avoid it altogether.
• Grow one type of microgreens in a tray. You can also grow multiple varieties in one tray, provided they all have the same growth rate. Again, this goes back to knowing your seeds as much as possible.
• Rotate the tray to ensure even sun exposure on all the microgreens. This usually applies to the ones getting natural light. It’s unnecessary for plants growing under artificial lights because they already distribute it equally to the plants.
• Harvest microgreens when they are 2-4 inches tall. The longer or taller you grow them, the bitter they tend to be. There are a few exceptions, such as pea shoots, lemon grass, wheat grass, and other grains. These usually have a better flavor when you let them develop more before harvesting. 
• Wash microgreens thoroughly with clean water before consuming them. They’ll usually last about 5-7 days before going bad. So if you want to keep them aside, don’t wash them and store them in the fridge.

FAQs

Final Words

Overall, microgreens need as much light as they can get once they germinate. While some may be ready within a week, others may take longer simply because of their seed variety and not the amount of light you give them. As long as you give them enough, they’ll happily develop until they’re ready for harvest. Happy planting!

References:

1. A Step-By-Step Guide for Growing Microgreens at Home. (n.d.). Penn State Extension. https://extension.psu.edu/a-step-by-step-guide-for-growing-microgreens-at-home
2. Grow Microgreens at Home. (n.d.). Purdue University – Extension. Retrieved August 12, 2022, from https://new.extension.purdue.edu/news/county/allen/2022/02/grow-microgreens-at-home.html
3. Growing Microgreens. (n.d.). Penn State Extension. https://extension.psu.edu/growing-microgreens
4. LED Grow Lights for Plant Production – Oklahoma State University. (2017, April 1). Extension.okstate.edu. https://extension.okstate.edu/fact-sheets/led-grow-lights-for-plant-production.html#devices-and-bulb-types
5. Lighting for indoor plants and starting seeds. (n.d.). Extension.umn.edu. https://extension.umn.edu/planting-and-growing-guides/lighting-indoor-plants#types-of-grow-lights-2651610
6. Microgreens – Gardening Solutions – University of Florida, Institute of Food and Agricultural Sciences. (n.d.). Gardeningsolutions.ifas.ufl.edu. Retrieved August 12, 2022, from https://gardeningsolutions.ifas.ufl.edu/plants/edibles/vegetables/microgreens.html
7. Microgreens Mountain View Garden Club. (2019). https://extension.arizona.edu/sites/extension.arizona.edu/files/attachment/Microgreens.pdf
8. Stivers, L., & Dupont, T. (2019, February 18). Seed and Seedling Biology. Penn State Extension. https://extension.psu.edu/seed-and-seedling-biology
9. The ABCs of Microgreens. (n.d.). Penn State Extension. https://extension.psu.edu/the-abcs-of-microgreens
10. What Are Microgreens? (n.d.). Caldwell.ces.ncsu.edu. Retrieved August 12, 2022, from https://caldwell.ces.ncsu.edu/2018/02/what-are-microgreens/