Seeds in Rockwool

Hi collective forum of more knowledge than I could hope to gain in a lifetime.

I browsed the forums for about an hour before realizing I’m probably the only idiot (or maybe just the first to confess?) to start their first grow in rockwool. Pests are a major problem in my area - it seemed like the safest way to keep my seeds moist without introducing anything that would kill it at the early stages.

Except user error. Here’s my first seedling - it’s an Auto Gelato and it sprouted within about 48 hours (total darkness under a dome, temp at exactly 70°, sometimes up to 72°) - today is day four(ish).

I’m concerned for a couple reasons: she’s droopy. She’s tall. (Okay, I’m not that worried here, I think I needed to put light on it about a day ago and I was gunshy - I just turned on a generic Amazon grow LED above her)

But the real worry is - mold? Being absolutely new to this, I’m unsure if the white fuzzy is harmful, helpful, normal, or a sure sign that I’ve murdered this absolutely optimistic seedling in the course of 72 short hours.

Any input would be stellar. (PS- the rockwool is damp to the touch but not wet - ie nothing drips off if I pick it up and give it a gentle squeeze).

I have 3 other seeds in rockwool still in darkness in my closet - they’ve been vibing for not quite 3 days now, no signs of a sprout but they’re fems and not autos - I’m not sure why but I feel like the longer germ time has some correlation. But should those be under light, too?

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The white fuzz at the stem base are roots forming laterally. Many have their lights on 24h at this point, I personally do 18h on. That tall skinny look is her stretching for light. She’s most likely over watered. You’ll want to ventilate and get a small breeze on her.

I should also disclaimer. I grow in soil, which is not a hydropo medium. But we can also find the right people to ask around here.

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Awesome, thank you. I hoped the fuzzy was normal (I’ve seen it on tomato plants before, but never on things I actually can grow like avocado trees). I’ll pop the dome and let her breathe. :heart_eyes:

If you do a quick search (:mag_right:) for rockwool you’ll be able to see growers that have done the same. Read their experiences and learn mistakes before you make them.

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Yeah, that’s how I arrived at realizing I should have turned lights on about a hundred years ago and not keep the rockwool “wet” etc.

There’s such a wealth of information, but my poor brain really wanted to be sure I didn’t immediately destroy the one successful seed I had rolling. :rofl:

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Haha trust me I get it. I didn’t find this place till I was in over my head on my first grow. You’ll get there


I pulled her from the humidity dome and got a fan/light on her. After however many hours it’s been, the cube dried up fairly well - I live in a desert so keeping humidity levels between 40-60 is absolutely an artificial process.

I just gave her a makeshift dome (ziplock bag) but didn’t add any liquid to the cube - it feels slightly damp and probably where it should have been all along. The light is around 12-18” from the sprout - seems happy and warm (the room I had to migrate her to is about 75°F.)

Nice. Welcome to the forum. If you have any questions or issues keto them posted in this thread. It’ll make it easier for you to track down everything you’ve needed.

Good luck!

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I made a secondary post about a separate problem- better to consolidate here? It’s about a soil plant- not really my ambition to grow I just ended up with one.

You’ll find it far easier to keep everything in one spot. It’ll make referencing a million times easier.

Just lost your new question and tag people using the @ symbol like this @Graysin and it’ll send an alert to whomever you want help from.


I don’t know who to tag who could be of assistance, but here’s the info:

Strain: allegedly “Lemon Tree”
Growing medium: soil, not sure brand
Watering schedule: once every few days, probably 1/2 liter or so of filtered tap water (average PH of my tap water is about 7.8-8, I’m gonna assume it was similar)
Nutrients: none used, but I have Fox Farms Big Bloom, Grow Big, and Tiger Bloom at my disposal.
Lighting: it has been under 50% power VS1000 for approx 48 hours. I’m afraid to pump up the power without knowing if it’s healthy. Lighting is probably too high - it’s about 5 feet from the top of the plant - again, didn’t want to lower if I was getting light burn.
Temp: averaging 68-70°
Humidity: 42%
In a grow tent, using a 6” carbon filter and duct fan inside to exhaust into the room.

So far all I’ve done is give it a spray down of an ivory soap/water mix to ward off any pests, peel away the blatantly dead growth, and give it 1 liter of ph adjusted water (somewhere around 6.0)

I’m of a mind to just leave it alone and see what it does, but I also wanted to know if there are any blatant warning signs I should be seeing. Everything under the top few leaves seems to begin to crisp up after a day or so, which has me wondering if it’s got nutrient burn?

Your pH is the cutest thing I’m seeing. 8 is WAY too high for cannabis. You want to be as close to 6.5 as you can. What are you using to test your pH?

I’m just using old school science lab style drops in a 10ml cylinder - I need a decent ph meter but couldn’t really decide on one. I’m using ph adjusted water - 5.8-6ish for my rockwool and that’ll be what goes into the DWC system once my seedlings are big enough to set into hydroton. I’m not sure how to test the soil ph without an actual soil ph meter (test the runoff I guess?)

I should clarify I’m not feeding the plant the tap water at 8 - I’ve given it 6.0-6.2ish water but only once since acquiring it. I don’t want to drown the thing, and the soil is already rather damp.

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For hydro yes. You don’t be able to without a good pH meter. Most often recommended is the blue lab

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Problem solved for my hydro grow then. Any suggestions for inexpensive ($30 or less?) testing essentials for the soil plant? I’d like to keep it alive if I can.

Same honestly. You’ll want to make sure the pH for soil is at 6.5 by doing runoff or slurry readings. Flush with pH water till what comes out matches. But this is one item you don’t want to skimp on, accuracy is key!

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@Underthestairs okay now I’m stumped. I flushed the plant with 4 gal of my purified tap water (I’m guessing this is about a 1.5 gal pot) - ph of 7.8 so I’d know exactly what I was putting into it. My runoff is right in the 6.4-6.6 range so I’m suspicious that the soil was too acidic (is that a thing?) before the flush. My ppms in the water used to flush was 108. The runoff is only at 231. If I’m not totally off my rocker does that mean this gal is way under-fed and was suffering a ph imbalance? (Boy are those relatable problems)

Any guidance would be appreciated. I’m not sure if now is the time to introduce a 1/4 strength nutrient solution or if I just need to let it rest for a few days and then add nutrients.

Yes, if your PPM are that low it’s time to start feeding. Depending on your nutes, you may want to start at reduced strength.

5x the amount of the pot in properly pH’d water for a full flush. Then my last gallon has full strength nutes (I use Jack’s 321).

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Super helpful, thank you. I’m going to have to mix up a gallon when I get back from work in a few hours. Right now I’ve just got the basic 3 from Fox Farms-
I’ve seen a lot of “start at 1/4th strength” guidance on the forums for this particular brand. But the plant also seems so starved I’m wondering if 1/2 or 3/4 strength wouldn’t be safe. I’ve got calmag on the way, since I’m certain it’s going to need extra supplementation based on similar struggles others have faced in the past.

I’d go at least 1/2 strength with how hungry she looks.

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