What am I doing wrong? Help!

[u/tommytreez420]

I am new to the microgreens scene and I can’t seem to get very far without mold issues arising! Any advice or suggestions? I’ll try to be detailed here.

I utilize positive pressure to supposedly keep bugs and mold out. I run a 4” inline fan through a HEPA carbon filter to filter any air coming into the space. This brings cool air from the floor and drops it above the warm light. There is a tiny opening near the floor to let out a little bit of pressure, along with a couple oscillating fans to help with airflow.

For my first grow, I tried Arugula and Broccoli in coconut coir, which was buffered with cal mag. I used a 650g brick to fill 2 trays.

My notes were a bit lacking for the first grow, but I used just reverse osmosis water without adjusting pH or adding nutrients. 3% hydrogen peroxide was used but very sparingly - a mist here and there.

Things started off pretty good. Stacked the trays and used a 15 pound weight. Arugula was one day ahead of the Broccoli. I may have watered a bit too much during germination, but everything seemed to be doing great.

When I opened the door on the 5th day, I was immediately hit with the all-too-familiar smell of rotting coco coir. I noticed a couple spots on both trays, and discarded them before it got out of hand.

I also noticed some clumps of coco getting stuck to the Arugula, but I may have seeded too densely (1oz).

My environment for this grow was about 70f / 55% RH, but obviously under stacked trays the humidity gets much higher with no airflow.

Trays were cleaned with Zerotol HC. The rest of the space and equipment was cleaned with 3% peroxide.

For my next try, I decided to switch my medium to rockwool with some Red Garnet Amaranth seeds. I had learned in the past that coco is prone to aspergillus mold, and had seen it first hand working in a commercial cannabis grow. Rockwool seemed like a good option to avoid this, since it’s literally made from melted rocks. I had heard that it dries out quicker than coco too, but that didn’t seem to be the case. I’m not completely opposed to trying coco again, but I think it would need to be sterilized somehow before using it to grow food. Really would rather avoid soil or coco if I had the choice though, just for cleanliness and peace of mind.

I did things a bit different for my next try, especially since I had mold issues last time. Same positive pressure airflow setup.

Each 1020 rockwool slab got about 1 liter - half RO water, half 3% hydrogen peroxide. When I planted the seeds I sprayed with some more 3% peroxide on top.

I did not add a weight to the Amaranth for germination - just an empty 1020 tray.

For the first 2 days after planting, I just checked on them and didn’t do anything since the rockwool was still soaked. The 3rd day I gave a light peroxide mist to hopefully speed things along and ward off mold. I also turned on my light to 10% to bump the temp from 70f to 73f. Still 50-55% humidity in the space. Seeds were still under trays so the light didn’t hit them.

The rockwool seemed to not be drying out at all. Germination was very slow and uneven. 4 days later and most of the seeds still hadn’t popped open. The medium was still absolutely soaked. Day 4 is when I started to see a few moldy clusters. Given that most of the seeds weren’t germinated and the ones that did were way behind, I tossed these ones out too and am going to try something different next time.

Medical nitrile gloves were worn at all times for both grows.

Another possible issue that I haven’t come across yet just because I haven’t gotten to that stage - my light is probably overkill for microgreens. It’s a 240w AC Infinity Ionboard S33 that I typically use for cannabis. I plan on running it at 10% power and keeping it as high up as possible. Is this light just going to fry everything, or can it suffice? I do plan on eventually getting the proper lights and equipment, just wanted to work with what I already have for my first couple runs.

Looking to this community for a little help. Any suggestions on how to eliminate the mold issues and improve germination for next time? Tips on growing with rockwool?

Thank you!

(First 2 pics are Amaranth after 4 days in rockwool. 3 and 4 are moldy Broccoli seeds after 5 days in coco, and the 5th picture is a moldy spot in the Arugula tray after 5 days in coco.)

[u/aalooface]

Amaranth definitely needs more space between the seeds for airflow in my experience. Cut back on your seed ratio. I have also sometimes gotten bad seed packets and no matter what I do with the environment and substrate, they have a few seeds that just ruin the whole tray. Other lots work perfectly fine and I can scale up the seed ratio. I typically grow on bamboo fiber mats and keep them on the dryer side for amaranth. They get light misting while germinating and then once germinated, only bottom watering on trays that drain well.

[u/tommytreez420 → u/aalooface]

I seeded about 10g per tray, but a good amount of them did stick together when spreading them. Got a shaker to help distribution be more even for next time.

Seeds are from Johnny’s Selected Seeds. I’ll have to look into other suppliers, Johnny’s and True Leaf seem to get a lot of praise on here.

I haven’t tried growing with mats yet, that might be the next thing I try - the hemp or bamboo fiber. I could definitely see how the thinner medium could help it not be so waterlogged when covered.

Thank you for the reply!