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Microgreen Troubleshooting: Fix Mold, Short Trays, and More

Most microgreen problems trace back to a short list of causes: light, water, timing, or the seed. This page collects every troubleshooting guide we have written, so you can find your symptom and go straight to the fix. Everything here comes from our own trays, which we have grown since 2018.

If you would rather have it all in one download, our free troubleshooting guide covers the common problems and a glossary of grower terms. Start there if you are new, or scroll to the symptom you are seeing.

Free Microgreen Troubleshooting, FAQ and Lingo Guide

A free PDF with troubleshooting steps, answers to common questions, and a glossary of microgreen terms.

Quick Checks

These are the first things we check when a tray is not growing the way we expect.

  • Leggy or stretched: not enough light, or lights too far away. Lower lights to 6 to 12 inches above the canopy.
  • Short or stunted: lights turned on before the tray finished its weighted and blackout phase, water quality or temperature problems, or no fertilizer on an inert medium.
  • Bleached or crispy leaves: lights too close. Raise them to 10 to 12 inches.
  • Uneven growth: uneven light across the shelf, or crowded trays blocking light. Rotate trays halfway through the grow.
  • Slow or patchy germination: check seed quality, soak and weight steps for that crop, and watering.

Mold and Root Hairs

How to tell mold from the fine white root hairs that are normal, plus prevention and treatment. It is our top troubleshooting guide, and the first one to open if you are unsure about a tray.

Why Are Your Microgreens Staying Short?

The common causes of short, stunted trays: light turned on too early, water quality, temperature, missing fertilizer on inert media, naturally short varieties, and seeding density. Distinct from leggy, stretched microgreens, which is a different problem.

Top Microgreen Growing Mistakes

The errors we see most often, including the causes of leggy or stretched microgreens. A good read before your first few trays and a quick audit if a grow went sideways.

Damping Off

What damping off is, how to identify it, and how to treat and prevent it.

Fungus Gnats

How to get rid of fungus gnats in indoor microgreen trays and how to prevent them coming back.

Weight and Blackout Timing

When to move a tray from the weighted phase to blackout and into light. Timing here is one of the most common reasons trays stay short. Our 4 tray weight experiment shows why weight matters during germination.

Watering

Bottom watering, top watering, volumes, and a schedule. If you are unsure whether a tray is too wet or too dry, start here.

Lighting

Light intensity, spectrum, duration, and the fixtures we use. Our fluorescent vs. LED experiment compares the two side by side. For setup, see our grow lights and rack setup page.

Feeding and Fertilizer

Which fertilizers work on soil and on inert mediums, and how to dilute them. The Free Fertilizer Ratio Guide has the dilution and pH ratios.

Seed Quality

Seed quality affects germination and food safety. Our guide covers how to choose seed, and our Microgreen Seeds page lists where we buy ours.

Reusable Grow Medium Problems

If a crop is struggling on silicone, check our seed compatibility guide, since Swiss chard, beets, and cilantro do not work well on it, and our cleaning and sanitizing guide for sheets that need a reset.

Microgreen Tracker

When a tray goes wrong, the hardest part is remembering what you did. In Microgreen Tracker, every tray has its own notes field and seed record, so you can look back at the light, seed, and timing behind a good or bad batch. It runs in your browser, installs to your home screen, and comes with a 7-day free trial. Try Microgreen Tracker Free.

Microgreen Masterclass

Our full course covers every method and its troubleshooting in 11 modules, if you want the whole system in one place. See what is inside in the course breakdown.

Troubleshooting FAQ

Why are my microgreens short?

The most common cause we see is turning the lights on before the tray finished its weighted and blackout phase. Other causes are water quality, temperature, missing fertilizer on an inert medium, a naturally short variety, and seeding density.

Why are my microgreens leggy or stretched?

Leggy microgreens usually mean not enough light, or lights that are too far away. Lower the lights to 6 to 12 inches above the canopy and use daylight spectrum LEDs in the 5500 to 6500K range.

Is the white fuzz on my microgreens mold?

Not always. Fine white root hairs are normal and are not mold. Our mold guide shows how to tell the two apart. If you are unsure whether a tray is safe to eat, do not eat it.

What is damping off?

Damping off is a problem that affects young seedlings and shows up in trays as a failure to establish. Our damping off guide explains how to identify, treat, and prevent it.

How do I get rid of fungus gnats in my microgreens?

Our fungus gnat guide covers how to manage them in indoor trays and how to prevent them. It is written for growers working with soil and coco coir indoors.

When should I turn the lights on?

Not until the tray has finished its weighted and blackout phase, which is around day 3 to day 5 depending on the variety. Turning lights on too early is one of the most common causes of short, stunted trays.

Do microgreens need fertilizer?

On an inert medium such as coco coir or reusable silicone, yes. We use Ocean Solution 2-0-3 at 0.5 oz per gallon with pH 5.5 to 6.0, and not on soil. Our fertilizer guide covers soil and hydroponic feeding.

Is there a free troubleshooting guide?

Yes. Our Free Microgreen Troubleshooting, FAQ and Lingo Guide is a free PDF covering common problems and a glossary of microgreen terms.

Not sure where to begin? Start with the free troubleshooting guide, then open the guide that matches your symptom. The Microgreen Masterclass is there when you want the full walkthrough.

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Our results and opinions come from our own grow space. Your climate, water, seed, and setup are different, so your results can vary. If you are ever unsure about mold or the safety of a tray, do not eat it. For our full terms, see our Disclaimer and Affiliate Disclosure.

Happy growing!