New Grower Think different guerrilla grow (what soil mix?)

[Dubboy]

Hi everyone,
good to be part of the auto crew,
first time growing autos and using soil,
I've got 16 think different all come through in 4'' rockwool, 8 are going in nft trays and the rest I'm putting outdoors guerrilla style,
my plan for the outdoors is to dig around 10ltr holes and fill with either plagron bat mix of biobizz all mix, my concerns are these mediums might be to strong for my babies cause there only 3'' tall, I won't be able to feed them again so I need a medium which will last to the end,
any information appreciated,
PEACE

 

[Somerset]

I want to hear these answers too, I'm a similar boat! https://www.autoflower.org/f6/outdoor-uk-first-time-journal-ref-34201.html