Hello there! Thanks for providing the pictures; they really help illustrate the situation you're describing with your broccoli microgreens.
You're right, it's frustrating when some trays thrive and others fail under seemingly identical conditions. Let's explore what might be causing your broccoli microgreens to "fall" or struggle, beyond just watering.
While microgreens generally don't require external nutrition during their short growth cycle because they primarily rely on the energy stored in the seed, lack of nutrition is highly unlikely to be the primary cause of your broccoli microgreens "falling" or failing. Broccoli microgreens, like most microgreens, are harvested at the cotyledon stage, before they develop true leaves or deplete the nutrients within the seed.
Based on the images and your description, where some trays are perfect and others fail despite similar treatment, here are the most probable culprits for your broccoli microgreen problems:
- Damping-Off
Disease: This is the most common and devastating issue for
microgreens, especially when growing in bulk. It's caused by various fungi
(like Pythium, Phytophthora, Rhizoctonia, Fusarium) that thrive in overly
wet, humid, or poorly ventilated conditions.
- Symptoms:
Seedlings appear healthy one day and then suddenly collapse at the soil
line, looking waterlogged or mushy, often in patches that spread. The
"falling" you describe strongly aligns with damping-off.
- Why
it's patchy: Even with similar treatment, micro-climates within your
growing area (e.g., slight variations in airflow, humidity, or initial
moisture levels) can trigger an outbreak in one tray but not another.
- Why
it's not nutrient related: Damping-off is a fungal disease, not a
nutritional deficiency.
- Seed
Quality Issues: Even within the same batch, there can be slight
variations in seed viability or contamination. If a sub-batch of seeds had
lower germination rates or was carrying a fungal spore load, it could
explain the inconsistent results.
- Substrate
Inconsistencies: While you might prepare your trays similarly, subtle
differences in how the substrate is spread, its initial moisture content,
or even slight compaction variations could affect germination and early
growth, making some areas more prone to issues like damping-off.
- Light
Issues (Less Likely for "Falling" but can cause weak growth):
While your lights look good, if specific trays are in slightly shadowed
spots or receive less intense light, the microgreens might become leggy
and weaker, making them more susceptible to collapsing, especially if
combined with overwatering or poor airflow. However, this usually presents
as uniformly weak, stretched plants rather than patchy collapse.
What to investigate and how to improve:
Given that some trays are perfect and others fall, and you've ruled out over/under-watering, I'd strongly focus on damping-off prevention and environmental consistency:
- Ensure Excellent Air Circulation: This is critical. Make sure your fans are positioned to provide gentle, consistent airflow across all trays, particularly those on lower shelves or in corners. Stagnant air is a breeding ground for fungi.
- Sterilize Equipment: If you reuse trays or tools, ensure they are thoroughly cleaned and sanitized between uses. Even residual fungal spores can cause issues.
- Maintain
Optimal Humidity: While consistent moisture is needed for germination,
high ambient humidity during the growth phase (after blackout) encourages
fungal growth. Aim for moderate humidity if possible.
- Bottom
Watering (Post-Germination): Once roots are established, watering from
the bottom keeps the top surface of the medium drier, which discourages
fungal growth on the stems.
- Substrate
Depth and Evenness: Ensure your growing medium is spread evenly at the
correct depth across all trays to promote uniform growth and drainage.
- Monitor
Temperatures: Consistent temperatures are important. Large
fluctuations can stress plants and make them more susceptible to disease.
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