Seedlings have stunted growth

My Grand Daddy Purple AF seedling seems really stunted. At day 10 past emergence she still only has the first true leaves with the tiniest second set starting (2nd set < 1mm across).

Light: GE LED grow floodlight on 18/6 timer, reads 240 PPFD on phone app, I’ve successfully grown using these lights previously, although I plan to switch once I get to veg stage
Soil: mix of Coast of Maine “Bar Harbor” organic potting soil and Jiffy organic seed starting mix (coc coir + peat moss), I’ve successfully grown in this medium before.
Water: every 4-5 days once the soil dries out, just until runoff, using grocery store spring water for now
Container: “solo” plastic cup with drainage holes, I’ve used these for other non-cannabis seedlings with no problems.

Unfortunately I had exactly the same experience with all of a previous batch of GDP AF seeds from ILGM. ILGM support was excellent and gave me another batch of seeds to try, but the exact same thing is happening. I did see some similar posts in recent months where people are complaining of severely stunted seedling growth.

The two things that I could possibly see wrong are:

  • somewhat high pH at 8.0 due to the spring water (the potting soil is 7.0 and the seedling mix is 6.5)
  • low humidity due to time of year

I will switch water and add a little acidifier to get the pH down around 6.5. I saw some suggestions to cover the seedling container with a misted clear cover of some kind to get the RH higher, although I might prefer to just mist the entire grow box somehow.

This just looks really weird to me. I haven’t seen any other cannabis seedlings do this, although it’s only my 4th grow, and non cannabis seedlings have also done well in this box. At this point, they should be growing additional sets of leaves. The previous batch of seeds just never grew bigger leaves, even after 3-4 weeks, and I’m concerned that I’m going to see the same thing again.

Does anyone have any suggestions for me? I’m really hoping to get something out of these seeds.


Couple of suggestions your water ph is way high you need to get that down to around 6.5 and humidity plays a big role with seedlings so I would put a humidity dome on top of the plants another solo cup would work fine


Totally agree with you. They need higher humidity. :blush::v:


:point_up_2: these 2 are most likely the issue particularly the RH. For seedlings to thrive the temps should be 78-82 and RH of 65-75%. Like the others mentioned, mist the inside of a clear cup and place it over the seedling for a humidity dome and water a ring outside the cup every 3 days or so. Remove the dome periodically for fresh air and re-mist :love_you_gesture:


Here’s mine at day 10, and the humidity runs at about 45%. My guess would be your ph with that coco and peat moss. Mine is in happy frog.

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Thanks for the feedback @dirtydave @Flitme @OGIncognito @Dexterado .

I put a humidity dome on top until my USB mini humidifier arrives, then I’ll try the humdifier so I can monitor the RH.

The potting soil and seed starter mix I’m using has a dry pH around 6.5 but the jug of spring water I was using had a high pH of 8.0. I just watered her with filtered tap water and measured the wet soil at 6.5 pH, so that should be good now.

I’ll be back in a couple of days to say how it’s going.


:point_up_2: I don’t understand this Growmie?

:point_up_2: are you using a soil PH probe pen? Soil PH is taken using 2 methods. A slurry test and the most accurate is taking equal parts of the medium and distilled water and stirring these then allowing ample time to rest. Strain this through a coffee filter and test the PH with a PH Pen, the PPMs or TDS can be checked at the same time. The 2nd method is run off, this is done when feeding or watering and 20% of what you’re pouring in the top comes out the bottom. Catch a sample and test PH and PPMS. Seedlings are too young for run off :love_you_gesture:


I have a couple of stunted Gelato Aotos; I believe it’s due to low humidity.

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Pics? I purposely did not use domes like @Hellraiser this grow just to see if I could get seedlings through dry winter heat without them. I do use a humidifier that is misting near the leaves but rarely can get my tent above 45%rh. Soil, ph, and temp play the biggest role in seedlings imo.


Thanks again to everyone who gave advice!

Six days later, I’ve corrected the pH and started using a humidity dome. I measured the pH of a tap water soil slurry (I have a Hanna pH pen) at 6.9, which is inside the zone I see recommended everywhere. The humidity dome has kept the soil moist for 6 days since last watering and there is a mist on the inside of the dome.

But the seedling hasn’t grown at all.

At this point I probably have to write this seedling off because it’s an auto, and by the time it starts flowering it won’t be big enough to bother with, even if it magically starts growing at a normal rate tomorrow.

I really don’t see what, if anything, I’m doing wrong here, now that the pH and the humidity are corrected. I’ll try the other seeds from this packet with different light levels and soil mixes to see if they behave differently. But I’ve now started 5 of these ILGM GDP autos and they all just stall out at the first true leaves. I can’t help but wonder if the AF genetics are the problem.


What’s the temps in the grow space? Low temps can stall seedling growth. 78-82 are ideal :love_you_gesture:

The thermometer reads 73F when the grow light is on. ILGM’s own grow guide says the seedling temperature range is 68F - 77F with the optimum at 73F.

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Your call but if you get the temps I posted you’ll see some growth :love_you_gesture:

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Dont look that bad, ajust some temp, low the ph arround 6.2 and they gonna start grow I believe, I creates a post with almost same problem, and after thenhunidity corrction, they start to develop, ok a bit slow but its going on! Look:

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Seems like you’re forcing seeds to grow in a crappy soil mix and blaming it on the seeds. Maybe try regular soil before wasting seeds on that mix. Who recommended you mix that?

Actually the nighttime temps might be the problem. They’re on a seedling mat but I don’t know what the temps are in the grow box when the grow light turns off. I’ll check that out.

The soil mix isn’t crappy. It’s a good quality organic potting soil and an organic seed starter, which I mixed in to get the pH slightly acidic. I got exactly the same results before with just the potting soil on its own and just the seed starter on its own.

You said this :point_up_2: then you said this :point_down:t5:

Coco or peat moss isn’t supposed to dry out :point_up_2:

Miracle grow grows excellent tomatoes but is hit or miss with autos. That’s how non cannabis soil works :v:

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Sorry I wasn’t clear, actually I was trying to say it’s mostly organic potting soil with a little organic seed starter mix added.

I’ve had a few successful grows before with just the Coast of Maine potting soil. I can certainly go back to just using that on the next try.

To keep track of night grow room Temps install minimum maximum thermometer