blackout dome for microgreens

When to Use A Blackout Dome for Microgreens

Blackout domes are an essential tool in microgreen cultivation. They optimize the growth environment during the initial stages. By understanding the domed blackout method, growers can significantly improve the quality and yield of their microgreens.

This method uses a cover to block light, creating conditions promoting certain characteristics in microgreens. Knowing when and how to use a blackout dome can make a notable difference in the success of your microgreen farming efforts.


The Domed Blackout Method Explained

The domed blackout method involves covering microgreens with a dome to block out light during their early growth stages. This technique serves multiple purposes, primarily to enhance stem length and strengthen the plants.

The general principle is to create a dark, humid environment that encourages the microgreens to grow taller as they search for light. This method is particularly useful for microgreens like peashoot, popcorn and sunflowers, that benefit from stem stretching and robust early growth, providing an optimal start for various types of seeds.


Benefits of the Domed Blackout Method

Using the domed blackout method offers several advantages for microgreen cultivation:

  1. Lengthening Stems:
    • The absence of light prompts crops to grow taller stems as they search for light, resulting in longer, more marketable microgreens.
  2. Promoting Growth of Thin-Stemmed Microgreens:
    • This method is particularly beneficial for crops with naturally thin stems, enhancing their overall structure and strength.
  3. Aiding Vertically Challenged Microgreens:
    • Microgreens that struggle to grow vertically can benefit from the blackout period, which encourages upward growth and prevents stunted development.
  4. Creating New Products:
    • By manipulating the growth environment with blackout domes, growers can produce unique microgreen varieties with distinct characteristics, adding diversity to their product offerings.


Process of Using the Domed Blackout Method

lighting for Microgreens

Germination with a Blackout Dome

To germinate microgreens using the domed blackout method, follow these steps:

  1. Prepare the Growing Tray: Fill the tray with a suitable growing medium, such as soil or a hydroponic mat.
  2. Sow the Seeds: Scatter the seeds evenly across the surface of the growing medium.
  3. Water the Seeds: Mist the seeds lightly with water to ensure they are moist.
  4. Cover with a Dome: Place the blackout dome over the tray to block out light.
  5. Monitor and Maintain: Check the moisture level daily and mist as needed to keep the seeds moist.

Typically, the blackout period lasts between 3 to 5 days, depending on the microgreen variety. The seeds should remain in complete darkness until they have sprouted and are ready to be exposed to light.


When to Remove the Dome

Knowing when to remove the blackout dome is crucial for successful microgreen growth. Indicators include:

  • Emergence of True Leaves: When the first true leaves start to appear, it’s time to transition.
  • Stem Length: Once the stems have reached an optimal height, usually around 1-3 inches, remove the dome.


Potential Issues with the Domed Blackout Method

While the domed blackout method can be highly effective, it’s important to be aware of potential issues:

  1. Root Hairs Development:
    • The high humidity under the dome can cause the development of root hairs, which are often mistaken for mold. These tiny white hairs are normal and indicate healthy root growth.
  2. Mold and Fungi:
    • Excessive moisture and poor air circulation can lead to mold and fungal growth. Ensure the growing medium is not overly saturated and that there is some air exchange to prevent these issues.
  3. Overextended Stems:
    • If left in the blackout too long, microgreens may develop excessively long stems that are weak and prone to falling over. Monitor the growth closely and remove the dome at the appropriate time.


Main Concerns When Using the Domed Blackout Method

  1. Managing Condensation:
    • Condensation can accumulate on the inside of the dome, leading to overly wet conditions. To manage this, occasionally lift the dome to allow excess moisture to escape.
  2. Solutions to Condensation Problems:
    • Use a dome with ventilation holes or manually ventilate by lifting the dome slightly. Ensure the growing environment is not too humid.
  3. Impact on Plant Health:
    • Excessive humidity and darkness can lead to damping-off, a fungal disease that kills seedlings. Proper ventilation and monitoring moisture levels can mitigate this risk.


Drawbacks of Using Blackout Domes

  1. Limitations and Negative Effects:
    • Overuse of blackout domes can lead to weak, leggy microgreens. It’s important to balance the blackout period with adequate light exposure.
  2. Alternative Methods for Creating a Blackout Environment:
    • Other methods, such as using blackout cloths or stacking trays, can also be effective in achieving similar results without the potential drawbacks of domes.


The domed blackout method is a valuable technique for enhancing the growth and quality of microgreens. By understanding the appropriate timing and management of the blackout period, growers can achieve optimal stem length and overall plant health.

While there are potential issues and drawbacks, these can be mitigated with proper care and monitoring. Overall, the domed blackout method is an effective strategy for producing high-quality crops, making it a worthwhile addition to any microgreen cultivation practice.



Do all microgreen crops need a blackout dome for germination? Not all microgreens require a blackout dome. It is mainly used for varieties that benefit from elongated stems and robust early growth.

How does a blackout period affect the growth of plants? The blackout period promotes taller stem growth and enhances the structure and strength of microgreens by mimicking their natural search for light.

So, why use the domed blackout method? Using the domed blackout method can improve stem length, overall quality, and marketability of microgreens, particularly for those with thin or vertically challenged growth.

When should I uncover my microgreens? Uncover microgreens when the first true leaves appear and stems reach 1-3 inches in height, ensuring a gradual transition to light.

How long to leave microgreens in the dark? Microgreens should remain in the dark for approximately 3 to 5 days, depending on the specific variety and desired growth characteristics.

When to remove weight from microgreens? Remove weight from microgreens once they have sprouted and are ready to be exposed to light, usually within a few days after germination.

When should I harvest my microgreens? Harvest microgreens when they reach 1-3 inches in height and have developed their first set of true leaves, typically 7-21 days after germination.