New grower here.
Four autos (Sensi Skunk Automatic), direct-sowed into their final 12L pots (with drainage holes) about a month ago. Seedlings came up after roughly a week, then growth basically stopped. In the past week two have started to move again, but only one of them actually looks healthy. One of the others has yellowing and some drying on the upper leaves. The remaining two are still barely doing anything.
Medium is a coir / wood fibre / compost mix with a 1–2 cm layer of expanded clay pellets at the bottom of each pot for drainage, pH 6.5–7.3, EC 1.5–3.5 mS/cm, limed with feed chalk, so I haven’t added any nutrients yet. Watering has been by hand and honestly a bit irregular.
Light is a 150W HPS on 18/6. The bulb is about 10 years old but has only a few months of actual run time on it. Tent is 75×75×160 cm, so the 150W fills it reasonably well — I’m measuring around 110 PPFD at canopy.
The tent lives in an unheated shed. Outside temps have been below freezing at night. Canopy air is held at 21–24 °C by a dual-stage controller with a 100 mm inline fan, and the hygrometer is NaCl-calibrated.
I don’t have a heat mat, and I’d guess substrate temps have been sitting around 15–17 °C for the first few weeks even though the air above is fine.
Photos of all four plants in daylight and the temp/humidity logs are attached.
Any ideas on what’s holding them back? Is this recoverable, or are they too far behind for autos?
Thanks for your help!
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A few things…
No, they won’t recover.
The substrate temp is way too low… At the very least, get them off the floor. Ideally, a nice thick piece of foam board insulation separating the pots from the cold floor…
Your medium needs aeration…perlite or similar…
I don’t know what feed chalk is.
Ensure you’re using decent quality compost…
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For coco I’d want pH 5.8-6.2
You lock out both Ca, and Mg over 7pH, as well as Fe and Mn
This is why you’re getting interveinal chlorosis.
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Curious about the wood fiber ya used. Onky reason I ask is along with those others issues..some wood products can leech N from the soil too.
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You want your soil to drain well and not stay soaked constantly, starting with moist not damp soil, water in the sprout with a cup or two, after sprouting, water in a ring about 4-5 inches from the center around the plant to encourage root growth,don’t worry, it will find water if your soil isn’t completely dried out. I like to water that way with max 3 cups for the first week or two, usually watering every 2-4 days or when the soil dries back a bit. After that water it in. lastly raise the pots of the ground to help keep temps better also if you have a dome you can put it over the plants at night. I would just start over at this point with a high quality soil meant for cannabis like fox farm or coast of maine. I like seed starter mixes because they support the seedling for the first couple weeks, after that I have total control of my feeding. Others put a seed starter mix in the top half of the pot and a full strength at the bottom and use only water until it finishes. Start with a good foundation and master the early weeks and you will have great success, good luck!
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Basically everything you listed is not great. All advice so far is solid imo. Except I think 110 ppfd is pretty low for anything over a couple days old.
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Welcome to AFN @honkdor 
From the pix, the medium looks like it was packed down some. Leaving it loose makes it easier for young plants to spread roots. Little air pockets hold oxygen for the roots. Over time the medium will naturaly settle but by then plants should be well established.
I’d ask the living soil members above for recipes or ratios and start fresh. 
Wood chips used for landscaping often are treated with fungicide, preservatives, and even herbacide chemicals!
Also uncomposted wood chips mixed into soil robs it of nitrogen.
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@GasPlease is correct! I was thinking dli not ppfd. My bad!
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