my thoughts is why not stick em in the ground now you have the option of growing outdoors ?
make all the different when they have unlimited space for the roots, also transfer from soil to a soilless medium might curse you some problems, PH need to be much lower in a soilless medium (5,8 instead of 6,5) so no matter what I would stick to soil now you started them out in it, even if you do decide to stick em in the ground (only reason I can think of not to is Bc. of thieves or low night temps) I would still make a nice soil mix and dig a big hole and fill it with the fresh soil mix of your own to give em a perfect start ..