Plants leaning at soil line

Hey all, I guess I spoke too soon about my plants looking great :frowning:
Today is the second day of hardening them off to move these clones outdoors for the rest of their grow. Yesterday everything went fine, kept them outside for an hour in a shaded area. Today, same place for two hours. Went outside to bring them inside and they were all leaning over to some degree the worst being about a 45 degree tilt. The bending is happening at the soil line or maybe just below it. I brought them in tied them up with bamboo and soft tie plant support wire.
I’m guessing the wind caused this but also probably the roots are weak or my medium is to thin. Besides supporting them like I have what can I do to help this from happening in the future when they’re outside for good in about a week? Is there something I can give them to increase root strength?
I’m growing in promix perlite and coco. 50/25/25 but will be switching to 100 promix when I transplant them into 20gal pots
Any ideas would be greatly appreciated.
The red line is where it looks like it was hinging, green line was where it was leaning before I tied them up.

Side note- I will be doing a horizontal trills after they get into their final pot. I’m just worried about moving them in and out during hardening, when I repot them and just having weak roots in general.
I laced the medium with a good dose of mycorhize when I moved them from 2 to 5gal pots root ball was full in the 2gal almost a month ago. Going to be transplanting them on July 1st into either 10 or 20 gal smart pots.
Again, thanks for the time and ideas

And yes I have two fans blowing medium on them while inside under t5’s before anyone asks

Not only has it not developed a strong enough root system most likely the stem is probably week? I’m not a pro and not really sure but from what I understand you can bury the stem even deeper add more soil even past those bottom leaves that you have that bottom growth. Then water it lightly and the base of the stem should start to sprout new Roots underneath the soil within a week’s time to secure strength and hopefully help with the upward vertical growth and prevent it from leaning in the Wind. I might be wrong but it’s a suggestion at least.