Welcome to your hydroponic microgreens lesson! This is a sample lesson.

Today, we'll focus on how to germinate microgreen seeds and—crucially—how to know when to transfer the seedlings from darkness (the “blackout period”) to lighted containers so they can grow lush and green.

Microgreens are generally more successful if they spend a few days in the dark after sowing, usually under a slight weight. This simulates the natural condition under which seeds sprout, namely in moist soil beneath a covering of soil. Therefore we control water, light and pressure for one to four days.

En-Es

1. The Blackout or Darkness Period

Microgreens are generally more successful if they spend a few days in the dark after sowing, usually under a slight weight. This simulates the natural condition under which seeds sprout, namely in moist soil beneath a covering of soil. Therefore we control water, light and pressure for one to four days.

- After seeding your trays (on a moist hydroponic mat or medium), cover them to create a dark, humid environment—this encourages even sprouting and helps elongate the stems slightly for a better harvest [4].
- Keep the trays covered for 2–4 days (depending on microgreen variety and ambient temperature).

2. Signs Your Seedlings Are Ready for Light

Look for these key indicators:
- Majority of seeds have sprouted: The tray should be filled with small, pale or yellowish shoots (these are the hypocotyls and cotyledons).
- Seed hulls popping off: Most seedlings will have pushed through their hulls, though some seeds may still wear them.
- Sprouts reach 1–2cm (½–1inch) tall and push against cover: If you see the tray lid rising up, or you can easily brush the seedlings with your hand, the blackout phase is complete [7].
- Uniform coverage: There shouldn't be bare patches; nearly all seeds should have germinated.

3. Transition to Light

- Remove the blackout cover and move the tray to an area with strong indirect sunlight or under grow lights (ideally 4–8in/10–20cm above the greens) [3][8].
- A good light spectrum is 4600K–6500K, and microgreens will benefit from 12–16 hours daily under lights [1][3].

4. After Exposure to Light

- Within 24–48 hours, your seedlings will “green up” as they begin producing chlorophyll and photosynthesizing.
- Rotate trays if the shoots lean toward the light for even growth [8].
- Continue bottom-watering to prevent mold.

1. El Período de Oscuridad

Los microvegetales suelen tener más éxito si pasan unos días en la oscuridad después de la siembra, generalmente con un peso ligero. Esto simula la condición natural en la que las semillas germinan, es decir, en tierra húmeda bajo una capa de tierra. Por lo tanto, controlamos el agua, la luz y la presión durante uno a cuatro días.

- Después de sembrar las bandejas (sobre una estera o sustrato hidropónico húmedo), cúbralas para crear un ambiente oscuro y húmedo. Esto favorece una brotación uniforme y ayuda a alargar ligeramente los tallos para una mejor cosecha [4].

- Mantenga las bandejas cubiertas de 2 a 4 días (dependiendo de la variedad de microvegetal y la temperatura ambiente).

2. Señales de que sus plántulas están listas para la luz

Busque estos indicadores clave:
- La mayoría de las semillas han germinado: La bandeja debe estar llena de brotes pequeños, pálidos o amarillentos (los hipocótilos y cotiledones). - Desprendimiento de las cáscaras de las semillas: La mayoría de las plántulas habrán atravesado sus cáscaras, aunque algunas semillas aún podrían tenerlas.
- Los brotes alcanzan de 1 a 2 cm (½ a 1 pulgada) de altura y presionan contra la tapa: Si ves que la tapa de la bandeja se levanta o puedes rozar fácilmente las plántulas con la mano, la fase de oscurecimiento ha terminado [7].
- Cobertura uniforme: No debería haber zonas sin luz; casi todas las semillas deberían haber germinado.

3. Transición a la luz

- Retira la tapa opaca y traslada la bandeja a una zona con luz solar indirecta intensa o bajo lámparas de cultivo (idealmente a 10-20 cm por encima de los vegetales) [3][8].
- Un buen espectro de luz es de 4600K a 6500K, y los microvegetales se beneficiarán de 12 a 16 horas diarias bajo las lámparas [1][3].

4. Después de la exposición a la luz

- En 24 a 48 horas, las plántulas reverdecerán a medida que comiencen a producir clorofila y a realizar la fotosíntesis.
- Rote las bandejas si los brotes se inclinan hacia la luz para un crecimiento uniforme [8].
- Continúe regando desde abajo para evitar la aparición de moho.

Ready for Light?	What To Look For
Most seeds have sprouted	Hypocotyls/cotyledons are visible
Tray lid lifting	Shoots 1–2cm tall, pushing up cover
Pale/yellow color ok	They green up *after* exposure to light
Nearly full tray	Uniform germination, minimal bare spots

Tip: If your seedlings look lanky and pale but haven’t emerged evenly, leave them covered another 12–24 hours and recheck daily. Too long in the dark can lead to weak stems, so err on the side of slightly earlier exposure to light if most signs are present[7][8].

Just remember: The ideal time to transfer microgreens from darkness to lighted containers is **as soon as the majority of seeds have visibly sprouted and begun to push up the humidity dome or blackout cover**—usually within 2–4 days after sowing. This ensures healthy, strong, and vibrant greens with maximum nutrient content!

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Sample Quiz

1. What is the main purpose of keeping microgreen trays in the dark with a slight weight after sowing?
a. To prevent pests from attacking the seeds
b. To simulate the natural conditions under which seeds sprout
c. To speed up the harvest by warming the seeds
**Correct answer: b**

2. For how long should most microgreen varieties remain covered in the blackout period?
a. 5–7 days
b. 2–4 days
c. 8–10 days
**Correct answer: b**

3. Which of the following is a sign that microgreens are ready to transition out of the blackout phase?
a. Seedlings are still mostly under hulls
b. Sprouts have reached 1–2cm and push against the cover
c. The tray has many bare patches
**Correct answer: b**

4. After removing the blackout cover, where should you place microgreens for optimal growth?
a. In complete darkness
b. In a cool, shaded area away from all light
c. In strong indirect sunlight or under grow lights
**Correct answer: c**

5. What should you do if microgreen shoots start leaning toward the light after the blackout phase?
a. Harvest immediately
b. Rotate the trays for even growth
c. Increase the tray weight
**Correct answer: b**