>>620795When they're grown, one to a bottle will be tight. If you leave them as close they will be competing for the same light and you will get as much spinach from 20 plants as you would from 1. The leaves will be smaller and better suited for salad.
But I assume the plan is to plant them into the ground once they're bigger. This will be damaging to the plants once their roots are interwoven and you have to cut them apart. You will get much better results with healthy roots aplenty.
It doesn't look like your equipment is expensive. Just put them into separate bottles, and be careful not to damage the roots, or any part. Damage now multiplies during growth.
