No. Root hairs help young roots take up water. They show up most on radish and broccoli.

Why Does Mold Keep Coming Back?

Mold needs still air, damp leaves and a crowded tray. Take those away, and most mold never starts. Sow a little less seed and run a fan across the rack. Water from below so the leaves stay dry, and sanitize trays between uses.

Is White Fuzz on the Seeds Mold?

Fuzz on seeds, stems or the growing medium is more likely mold, since root hairs grow only on the roots. Mist it to be sure: root hairs disappear for a minute, and mold stays.

What Does a Sour or Musty Smell Mean?

Mold can smell musty. A sour or rotten smell usually means bacteria are growing where it's too wet. Rinse or drain it and add airflow. Smell it again in a few hours. If it still smells rotten, compost it.

Microgreens Mold vs Root Hairs

Root Hairs Are Healthy

Young roots grow fine white hairs that look like fuzz. They're healthy, and they help roots take up water. Beginners often mistake them for mold. Radish and broccoli grow a lot of them.

Cress seeds sprouting on dark growing medium, with fine white fuzz on their new roots — Cress sprouting. The fine white fuzz on the roots is root hairs, not mold.

Side by Side

Root hairs and mold compared
	Root Hairs	Mold
Where It Grows	Only on the roots, evenly across the tray	On seeds, stems or the growing medium
How It Looks	Fine, bright white fuzz	A gray or white web, often in patches
When You Mist It	Disappears for a minute	Stays, and can smell musty
What to Do	Nothing. They help roots take up water.	Scoop it out, or throw the tray out if it covers much of it

The Mist Test

When you're not sure, this takes a minute and settles it.

Look where it grows. Root hairs grow only on the roots, evenly across the tray. Mold grows on seeds, stems or the growing medium.
Mist a small spot. Spray a little clean water on the fuzz.
Look again. If the fuzz disappears for a minute, it's root hairs. If it stays, treat it as mold.

Which Microgreens Grow Root Hairs

Radish and broccoli grow a lot of them, so they're the trays that worry new growers most. Here's what their growing steps say to expect:

Radish (Daikon), Blackout: Seeds crack open and send down roots. Fuzzy white root hairs on the roots are normal.
Broccoli, Blackout: Seeds sprout and roots reach down. Short white root hairs are normal.
Kale (Red Russian), Blackout: Seeds sprout and roots reach down. Short white root hairs are normal.
Red Cabbage, Blackout: Seeds sprout and roots reach down. Short white root hairs are normal.
Kohlrabi (Purple Vienna), Blackout: Seeds sprout and roots reach down. Short white root hairs are normal.
Mustard (Red Giant), Blackout: Seeds sprout and roots reach down. Short white root hairs are normal.
Broccoli Sprouts, Rinse and Drain: Small white tails appear by the second day and grow longer each day. By the last day they fill about half the jar, with small pale leaves. Fuzzy white root hairs are normal.

What to Do About Mold

Scoop out the patch and a little around it. Mist the spot with 3% hydrogen peroxide mixed half and half with water. Then run a fan across the tray.

If mold covers much of the tray, throw the tray out. Then clean and sanitize the tray, and anything it touched.

When to Throw It Out

Some problems can be fixed. Others mean the tray or jar should go in the compost. When you're not sure, throw it out. One lost tray costs far less than a sick customer.

Throw it out when:

Mold covers more than a small patch, or comes back after you remove it.
It smells sour or rotten.
The sprouts or stems feel slimy.
An animal, pest droppings or floodwater got to it.
It was dropped on the floor.
The harvested greens sat warm for hours.
Its seed lot is linked to an illness or a recall.

Be stricter with sprouts. A sour smell or any slime in a jar means the whole jar goes.

After you throw it out, mark the tray or jar as failed in the app. Then clean and sanitize the tray or jar, and anything it touched.

Sources (checked October 12, 2026)

This is general information. Follow FDA guidance and your state and local rules.

How to Prevent Mold

Mold needs still air, damp leaves and a crowded tray. Take those away, and most mold never starts.

Keep air moving. Run a fan across the rack once trays are under the light.
Water from below, so the leaves stay dry.
Don't sow too much seed. Use the amount in the growing steps, and spread it evenly.
Clean and sanitize every tray between uses.
Keep the Grow Room between 65 and 75 °F, with humidity around 40 to 60%.

During blackout, check each tray every morning. Mist only when the surface looks dry.

If mold does show up, scoop out the patch and a little around it. Then add airflow for the rest of the tray. Log it on the tray, so your history shows what keeps causing it.

If mold covers much of the tray, throw the tray out.

Fuzz or Slime in a Jar of Sprouts

Be stricter with sprouts. A sour smell or any slime in a jar means the whole jar goes. These are the usual causes when sprouts turn slimy or brown:

Not Rinsed Often Enough: It's been more than 12 hours since the last rinse. Rinse morning and evening, every day.
Too Warm: The jar is near a window, appliance or heater. Keep jars around 65 to 75 °F.
Too Crowded: The jar is packed full and sprouts are pressed together. Start with less seed per jar.

See How to Grow Sprouts in a Jar for rinsing and draining that keeps jars fresh.

Check It in the App

Microgrower's Is This Normal check shows a picture of each problem, the likely cause for your tray's day, and a test to tell them apart. Sprout, the app's optional AI helper, can also look at your photo and tell you if it sees mold or root hairs.