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black out seeds

Microgreens and When to to Use a Blackout Dome

Nick & Nathan from On the Acre in Houston, TX discuss the topic.

When to Use Blackout Domes?

We do not use blackout domes unless we have selected that product to grow in blackout specifically. It’s not a regular part of our germinating or planting process. When they’re stacked, the trays are mostly blacked out, and beyond that, we haven’t found it necessary or beneficial to use that method.

What are the Drawbacks to Using Blackout Domes?

I worry, if you’re trying to germinate seeds in a blackout dome, you know there’s no light, and there’s no air movement, and that moisture is just sitting there not going anywhere, so you run the risk of mold or fungus issues that you wouldn’t encounter otherwise.

Why do you think that that’s such a prevalent problem saying that people are always told to do that blackout? Where did that idea come from? I have no idea; my best guess using domes would be best for people trying to create additional mass; they would use a blackout dome to lengthen the stems. The lack of light causes the stems to stretch toward the light. When there’s no light present, they’ll continue to grow and grow, and then they can cut at the very bottom, you know, with these long stems and little leaves on top, and they would be able to get more money because they’re selling by mass rather than volume.

Stacking During Germination Vs. Black Out Dome

Using blackout domes would use extra space. Our domes take up more space than when we stack the trays. We do two-three times as many in the same space without domes, so if we use that regularly, we would need so much more room to do what we’re doing, and for us, space is a premium. I talked to one of our students a couple of weeks ago, and they’re asking how to grow a new variety. They said that they needed like 25 trays a week or something, and they were planning on using blackout domes, and I was like do you know how much space that’s going to take? I advised them to use a stacking system because arranging 25 trays a week under blackout domes will use a lot of space.

Using Blackout Domes to Create New Products

Just as an option and the products you get when you use a blackout dome, it’s noticeably different like Nathan said, the stems are longer; they have a different color; they have a different taste. We do peas, corn, and sunflower currently in blackout domes.

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We have been experimenting with other stuff, but amaranth is next. It gives us another option, and we like to present our chefs with options. It’s just another product that we can offer from something that we’re already growing in non-black out domes. But the point here is, we’re growing it in its entirety in a blackout dome. We’re not growing it for just the germination period, then moving into the light. We are creating completely different products with the use of blackout domes.

How Much Weight To Put On Microgreens? (Which Need It? – Solved!)

You’ve started growing microgreens or you’ve begun looking into it. You want perfect, plump sprouts and greens. Grocery stores and restaurants are more likely to buy if everything’s uniform.

I wanted to know this as well as I’ve been having issues getting my microgreens uniform. I heard weight was the answer. But which microgreens need weight and which can you grow without it? Do they need a blackout period?

The microgreens that need weight are kale, sunflowers, and radish microgreens. Weight leads to faster and more thorough germination which means you can get your microgreens to market faster. This happens because covers and weights prevent the soil and seeds from drying out when germinating, builds thicker stronger first stems, and helps seeds shed their hulls.

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Why You Need Weight When Starting Trays

The weight keeps seeds moist and helps with even, fast germination. This means each tray gets to market (or your kitchen table) faster.

  • More seeds will successfully germinate (fewer duds)
  • Faster germination – This means you’ll get to the final product faster.
  • Prevents the seeds from drying out
  • Traps humidity in the soil
  • Keeps good contact of the seeds and the soil
  • Loosens the hulls so your plants can shed them easier and you can rinse them off faster (cleaner end product)
  • Roots dig deeper into the soil

Which Microgreens Need Weight

  • Kale
  • Sunflower
  • Radish
  1. Tray Cover Only
  2. Tray With Cover and 3 lb weight

Grow these to completion over 10 days then harvest and weigh the results.

How Much Weight Do You Put On Microgreens

The amount of weight will vary depending on the type of seed. Based on previous experiments here are a few rules of thumb to follow: Broccoli doesn’t need any weight. It just needs a cover to keep in the humidity. Radishes do best with 3 lb weights per tray. Kale also doesn’t require much weight. 3 lbs are sufficient.

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See the video below for more.

When To Put Weight on Microgreens

Use weight during initial germination.

Fill your tray with 1 inch of substrate. Add 10 grams of seeds. Then water till moist and let drain.

Add another tray as a cover than a 3 lb weight.

How Long To Use Weight

Leave the weight on for the first 3-4 days. Once all the seeds are germinated it’s time to move on to the blackout period.

Materials Needed

Using weights for microgreens is easy. All you need is a small 3 lb sandbag or similar weight and an empty growing tray.

Results Of Weight Experiments On Different Microgreens

Kale Microgreen Weight Results

In the video below On The Grow did an experiment with weight on kale microgreens.

They ran the experiment with four trays. Each tray used 10 grams of kale seeds and about 1 inch of coco coir media as the growing substrate. All were watered the same amount.

The only variations were the type of cover and the amount of weight.

Experiment Setup
  1. Control – The first tray was a control group. It had 1 inch of coco coir topped with 10 grams of kale seeds. No weight or cover was used.
  2. Paper Towel Only – The second tray used 1 inch of coco coir topped with kale seeds then covered by a wet paper towel.
  3. Tray Only – The third tray has 1 inch of coco coir topped with seeds. Then it was covered by another 1-ounce tray that added a very small amount of weight, partially blocked the light, and helped keep in humidity.
  4. Tray with 7 lb weight – The fourth tray used 1 inch of coco coir topped with kale seeds. It was covered by a tray and a 7 lb weight.
Experiment Results After 4 Days
  1. Control – Virtually no germination
  2. Paper Towel Only – Good germination but young sprouts
  3. Tray Only – Full germination with strong sprouts
  4. Tray with 7 lb weight – Full germination with strong sprouts and roots deep in coco coir

Broccoli Microgreen Weight Results

  1. Tray cover only
  2. Tray with 3 lb sandbag
  3. Tray with 15 lb weight

In the video below you can see that visually the results were pretty much the same.

They harvested and weighed all the final microgreens.

In the end, they all weigh about the same as well. The 15 lb group was a little longer. Strangely the 7 lb group had less weight than the no weight group.

Final verdict – Weight doesn’t seem to help broccoli.

The Radish Experiment

On the Grow did a third experiment with radish microgreens. It was the same setup as the broccoli experiment. This time though the 3 lb weight had a higher yield than no weight or 15 lbs of weight.

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This is just further proof that you need to test different weights for your variety and your chosen microgreen substrate.

Final verdict – Weight does help radishes. 3 lbs per tray are best.

What Is The Microgreen Blackout Period?

The blackout period is when you place a cover over the seeds when you are first starting them. This mimics burying the seeds in the soil and helps triggers your seeds to sprout.

You wouldn’t use real soil to cover them as that would just give you a dirty end product. It could also cause root rot or other diseases.

Purpose of the Blackout Period

The purpose of the blackout period is to get your seed sprouts to stretch. Without access to light, they’ll stretch tall trying to find it. This makes it much easier to cut and harvest them later.

Many microgreens don’t naturally like to grow tall in the first 7-10 days before harvest. The blackout period forces them to do this.

Luckily a non-transparent drain tray does this job perfectly. Simply flip it over and place it over your microgreens.

Some space is needed so if the tray is too shallow you’ll want to use something larger.

Blackout Vs. Weight – What’s More Important?

Both! The blackout period adds the darkness that simulates seeds being stamped into the soil.

The weight keeps in humidity and inspires the roots too deep for moisture and nutrients.

Not all microgreens need weight. Many work great just with the tray to induce a blackout and keep in the humidity.

Blackout Materials

The easiest material to use is just another tray like the one you’re growing in.

First prep a tray with growing media and seeds. Water till moist and let drain.

Then simply place an empty tray on top of the prepped tray. Remember that sprouts need space to stretch so be sure to use a tray that’s deep enough to give them growing room.

You can also use towels, cutting boards, plastic sheeting, cardboard, or anything else that’s safe to eat off of and that blocks all the light. However, many of these items don’t offer enough space. In combination with a clear cover, they can work great.

How Long To Blackout

Check your seed germination times for your specific setup. Keep them under blackout for 1-2 days longer than germination. This helps set the roots deeper and build stronger stems.