Help Diagnose My Seedlings Please!

First real post but I’ve been lurking for a while. I’m wondering if anyone can help me diagnose my seedlings and give me some tips to get them growing again.

They’re 18 days old from seed, one has grown much more than the other as you can see in the pictures. The larger one is a White Widow Auto and the smaller one is an OG Kush Auto

The White Widow seems to be getting lighter in colour and the cotys are yellowing. I suspect the cotys yellowing/browning is the natural process but I’m unsure about the lighter leaf colour especially on the little OG. The WW has shown some signs of growth over the past few days, but the OG has been stalled for over a week with the only change being its colour.
Here’s some grow info

-3x3 tent
-4” carbon filter
-Mars Hydro TS1000 (recently turned down the intensity a bit because I thought maybe I was light bleaching them
-rockwool cubes (pre-soaked in a mild nute solution initially)
-seedling heat mat (bottom of cubes register at around 78-80f)
-temp under the dome generally hovers around 25-26C lights on and 20C lights off
-20 hours lights on, 4 hours lights off
-humidity fluctuates between 40% and 80% depending on when I get time to add a bit of water to the tray only (not watering the seedlings)

So initially I believe I was over watering them.I used plain tap water at room temp for the first week or so before switching to a very mild nutrient solution (1/4 strength)
The lighter colour and yellowing cotys scared me into switching back to just plain water.
Now I wait until the cubes feel light and just slightly damp to the touch before watering again.

What do you guys think? Why has the OG stopped growing and why are they both turning lighter in colour? I believe they should be further along in their development at 18 days. I wish I had never used rockwool because I believe they have led to over/under watering and nutrient issues but this is the situation I find myself in and need some of your collective expertise!

cheers

Maybe theres too much nutes from the mild solution you soaked the cubes in. I would hold off until they are bigger IMO, keep them moist but not soaked.

Those cubes look soaked, they are only supposed to be for starting seeds, what is going to be your final medium as I would move them into it

Edit: cubes dont look that wet actually but I would definitely move them into whatever your going to be growing in be it hydro, coco or soil

MrGreenFingers99 said:

Those cubes look soaked, they are only supposed to be for starting seeds, what is going to be your final medium as I would move them into it

Edit: cubes dont look that wet actually but I would definitely move them into whatever your going to be growing in be it hydro, coco or soil

Click to expand...

It was my understanding that you’re supposed to wait until the roots begin to show through before moving them to in my case, soil. That’s what I’ve been waiting for. I thought maybe the stunted growth could be because all of the current growth is happening in the roots right now, but since both seedlings are experiencing the same “pause” in growth at completely different stages, it made me question that theory and come here.

BostonBuds said:

Maybe theres too much nutes from the mild solution you soaked the cubes in. I would hold off until they are bigger IMO, keep them moist but not soaked.

Click to expand...

I dip the bottoms in water for 2 or 3 seconds and then that kind of wicks up. It’s the only way I’ve found that doesn’t get them too soaked

BobChukowski said:

It was my understanding that you’re supposed to wait until the roots begin to show through before moving them to in my case, soil. That’s what I’ve been waiting for. I thought maybe the stunted growth could be because all of the current growth is happening in the roots right now, but since both seedlings are experiencing the same “pause” in growth at completely different stages, it made me question that theory and come here.

Click to expand...

Yeah but surely you can see roots? I use rockwool to germinate my seeds and pretty much as soon as they sprout the taproot is showing out the bottom of the cube and then I move it into my DWC system

MrGreenFingers99 said:

Yeah but surely you can see roots? I use rockwool to germinate my seeds and pretty much as soon as they sprout the taproot is showing out the bottom of the cube and then I move it into my DWC system

Click to expand...

Nope, I don’t see any roots coming out at all. Could it be that these particular cubes are too dense and these plants are just not growing for that reason?

BobChukowski said:

Nope, I don’t see any roots coming out at all. Could it be that these particular cubes are too dense and these plants are just not growing for that reason?

Click to expand...

Hhhhmmm, that's weird man, are you using any kind of root stim like Rhizotonic or anything with kelp in it? These are my roots after 1 week out the cube.

MrGreenFingers99 said:

Hhhhmmm, that's weird man, are you using any kind of root stim like Rhizotonic or anything with kelp in it? These are my roots after 1 week out the cube.
View attachment 4561037

Click to expand...

The only thing I had been using was my starter nutrients diluted in water. I soaked the cubes in it for germination at the manufacturers suggested amount For conditioning growth medium, in my case rockwool, and I was using this at about 1/4 strength starting at around day 7 once some true leaves were showing. The manufacturer suggested roughly 1/4 strength as a nutritive supplement. I have since stopped nutrients completely when my plants stopped growing and started to become lighter in colour. I have been using just straight water at room temp for the past 4 days or so. I may have wet the cubes twice during that time period. This is the starter nutes I’ve been using.
Here’s a quote from the description

“Nutri+ ® START was designed to treat propagation media to promote root development.
Nutri+ ® START contains all necessary elements to adequately supply the initial rooting stage of your cuttings or seedlings.”

BobChukowski said:

The only thing I had been using was my starter nutrients diluted in water. I soaked the cubes in it for germination at the manufacturers suggested amount For conditioning growth medium, in my case rockwool, and I was using this at about 1/4 strength starting at around day 7 once some true leaves were showing. The manufacturer suggested roughly 1/4 strength as a nutritive supplement. I have since stopped nutrients completely when my plants stopped growing and started to become lighter in colour. I have been using just straight water at room temp for the past 4 days or so. I may have wet the cubes twice during that time period. This is the starter nutes I’ve been using.
Here’s a quote from the description

“Nutri+ ® START was designed to treat propagation media to promote root development.
Nutri+ ® START contains all necessary elements to adequately supply the initial rooting stage of your cuttings or seedlings.”

Nutri+ START

FREE shipping on eligible orders over $149. Discreet delivery in Canada. Lowest price on Nutri+ START guaranteed with our Price Match Guarantee. Financing available.

indoorgrowingcanada.com

Click to expand...

Ok well just feeding water is really not helping, the plants need food to grow! Normally root stim and starter nutes you can feed at full strength, it's just when you start adding your base nutrients then you want to go lower then suggested amounts, also are you PH'ing your water?

Roots don't grow when they don't like what they are growing in. I see it from time to time in my DWC buckets. If the PH or EC is too far off the roots won't grow. They get bitter beer face lol. If I had your sickly rockwool cubes I would throw them in Pro Mix under a T8, and when that tap root finds some nice Pro Mix it will take off. Hopefully it will do the same in your mystery soil.

MrGreenFingers99 said:

Ok well just feeding water is really not helping, the plants need food to grow! Normally root stim and starter nutes you can feed at full strength, it's just when you start adding your base nutrients then you want to go lower then suggested amounts, also are you PH'ing your water?

Click to expand...

I have not been testing or adjusting the PH of the water. I realize this could lock out certain nutes and I will be investing in some PH equipment ASAP. My reasoning for stopping the nutes was just thinking there could be a build up of nutrients within the rockwool since when watering they don’t really drain off or drip but just dry out through evaporation, so wouldn’t that mean any unused nutrients would build up in the medium itself and then wouldn’t continuing to feed them each time when they aren’t growing just continue to cause those nutrients to build up? I thought this could be the reason for the colour turning much lighter hence cutting back. Since switching to plain water, the White Widow has shown some signs of perking up but the colour change remains constant. I am a newbie after all so I’m just trying to think logically with my limited experience.

70's natureboy said:

Roots don't grow when they don't like what they are growing in. I see it from time to time in my DWC buckets. If the PH or EC is too far off the roots won't grow. They get bitter beer face lol. If I had your sickly rockwool cubes I would throw them in Pro Mix under a T8, and when that tap root finds some nice Pro Mix it will take off. Hopefully it will do the same in your mystery soil.

Click to expand...

I will be using Stepwell SS-W super soil. Would you suggest throwing these cubes in a solo cup with some soil or just directly into their larger permanent homes?

I threw 2 more seeds into some rapid rooter plugs to see if I can catch up to these two rockwool seedlings. I feel like the rockwool was just a bad idea for a beginner.

Being that these are all Autoflowering strains, are they still only going to have the same lifespan as far as time goes and probably be runts if they ever take off? Or do they just wind up taking longer than the 8-10 weeks?

BobChukowski said:

I threw 2 more seeds into some rapid rooter plugs to see if I can catch up to these two rockwool seedlings. I feel like the rockwool was just a bad idea for a beginner.

Being that these are all Autoflowering strains, are they still only going to have the same lifespan as far as time goes and probably be runts if they ever take off? Or do they just wind up taking longer than the 8-10 weeks?

Click to expand...

Ok this time as soon as they sprout get them into your soil, I would personally start in solo cups but people say it's not good to transplant autos so you could go to your final pots but it's harder to get your watering right with a seedling in a large pot, I would also move the other 2 in rockwool into soil as well

MrGreenFingers99 said:

Ok this time as soon as they sprout get them into your soil, I would personally start in solo cups but people say it's not good to transplant autos so you could go to your final pots but it's harder to get your watering right with a seedling in a large pot, I would also move the other 2 in rockwool into soil as well

Click to expand...

I think I’ve read that transplanting more than is necessary causes additional stress/recovery time and for a plant with a built in timed life cycle like auto flowers have, this could diminish your return come harvest. In other words the clock is ticking. This is why I was wondering if these 18 day old seedlings will still grow to their full or at least reasonable size before flowering or if they will forever be the runts of the litter with very low yields if any. I guess only time will tell!

BobChukowski said:

I will be using Stepwell SS-W super soil. Would you suggest throwing these cubes in a solo cup with some soil or just directly into their larger permanent homes?

Click to expand...

A Solo cup would be pretty temporary, I would prefer to go one size bigger,like half a 2 liter soda bottle. I don't know what size the final home is but it is better to up-pot gradually to build a nice root ball. I'm not familiar with your particular soil but it should be fine and if it's a little hot the plant will usually adapt.

BobChukowski said:

I think I’ve read that transplanting more than is necessary causes additional stress/recovery time and for a plant with a built in timed life cycle like auto flowers have, this could diminish your return come harvest. In other words the clock is ticking. This is why I was wondering if these 18 day old seedlings will still grow to their full or at least reasonable size before flowering or if they will forever be the runts of the litter with very low yields if any. I guess only time will tell!

Click to expand...

This is all very true but I've seen people transplant autos without any issues, also it's true your returns are going to be diminished on those 18 day girls but as you are a noob I would use these for learning experience at least so I would continue with them myself to get some experience.

70's natureboy said:

A Solo cup would be pretty temporary, I would prefer to go one size bigger,like half a 2 liter soda bottle. I don't know what size the final home is but it is better to up-pot gradually to build a nice root ball. I'm not familiar with your particular soil but it should be fine and if it's a little hot the plant will usually adapt.

Click to expand...

I will be using 7gal fabric bag style pots

Little update. I’ve not transferred the cubes to soil yet as I was really hoping to see some roots come out of the cube soon and I also would like to just hold off until my two new seeds I started in rapid rooters pop so I could get them all in soil at once. If the roots start to show sooner than the new seeds pop I’ll put them in their pots separately. Just wanted to post an updated picture of her growth over the last 30 hours or so. Heres the picture from yesterday and one from today I’m happy with the growth but the yellowing is still an issue. I don’t know that 30 hours is long enough for any colour to come back but would this new growth be a positive sign that this thing will make it? I wish the roots would come through as I’m worried they are locked in there or something.