How long ago did you plant your starts ?
The optimal mix according to the square food gardening method is 1/3 peat 1/3 vermiculite (or perlite ) 1/3 compost. I use a 1/2 compost (if store bought it is two type any two types will do just to get a well balanced compost ) 1/2 peat based potting mix. I also mix in there a wide spectrum trace mineral called Gia green glacial rock dust. You can replace that with azomite in the US. Or my garden I find that mix in just regular pots works best. If it is self watering I change it.
The reason I ask is if you just plants them you have a fair chance you can re-pot them. I have a video on potting on my YouTube channel below.
From the looks of it that is a tomato and you can plant it deep as well
(tomorrow's video will show that)
Good luck my friend