HELP! Stunted grow (first time growing autoflower)

[7ALA]

Dear all,

TLDR
Does anyone have an idea why my plant growth is stunted like this?

I'll try to give a short description of my situation:
- Outside if possible (20C/68F minimum + not cloudy), in my room otherwise (70F, in homemade cardboard box, 40CM from 10W LED growlight E27 (2/3s red, 1/3s blue, warm white, cold white, IR, UV)
- Growing in 'seedling soil' with 20% perlite added (picture of soil description added)
- Lower side of recommended 'slow release' nutrients added to bottom 2/3s of soil mix
- 12L/ 3.2gallon pot size (plastic, added holes in the bottom for drain-off)
- combination of water (tap water 7.8pH, Spa 6PH, mineral water 7.2pH)

Watering history (days)
1: 100mL/3.4oz (just sprouted, under mostly warm lamp)
2: 100mL
6: 100mL
7: 35mL (ground seemed very dry)
9: 100mL
11: 100mL
13: 150mL
15: 150mL
17: (today) haven't watered in the last couple of days since plant is indoors and sun is not shining (soil still moist below top layer)

Plant was mostly outside in the first 1.5 weeks, but has been staying in for the last week.
I've ordered an RH-meter, pH strips and pH meter for soil, these will not arrive for some time.

Pictures:
Days 3, 7, 9, 13 and 16 (twice) as well as soil.

She's still growing but things are moving along very slowly.

I hope to hear from someone more experienced soon!

 

[Canuck147]

They take a while to fill the pot with their roots - then grow up.
My autoflowers in 2 gallon pots sit like that for 7 to 10 days before they take off.
Let them dry out between waterings - don't drown them.

 

[bboyfromwayback]

That’s how mine were the first time I grew autos, took them until day 21-24 before they finally grew. The next time I sprouted them in 6oz styrofoam cups sitting on a heating pad with a bag over the top. I moved them into 2 gallon pots after 10days and they were all 4-6” tall and bushy. Be patient this round