plant spacing

Seemingly contradictory statements:
Most plants can be grown in containers.
vs. Allow 12" between rows.

Our veg patch could be enlarged a bit, but there are also sunny/warm spots where I'd be inclined to try containers instead. Having also heard of the phenomenon called 'square foot gardening,' I am well-confused about how densely to plant out the veg patch.

Thinking of sowing perpetual spinach in a rectangular container... but would that be only one row?

 

Or sow/plant thickly and thin out?

 

Once sowed perp spinach in a 2' trough-type container by scattering seed over soil surface. Result: crowded plants all ready at the same time. Love greens but can't scoff that many @ one go.

Continuing to sow basil on windowsill 5 seeds/station, 15-16 stations/container. This avoids the problems of fussiness growing it outside; little plants all bunched up don't quite 'mature,' leaves don't grow as large, but still delicious and plentiful enough for freezing to keep us in Italian-American dishes through winter.

Not much point in growing two 36" rows of beetroot except as experiment; if successful, OH will want to know the reason why more weren't sown (me too, I never saw a beetroot I didn't like). Outdoor-actual-mother-earth patch this year I'm hoping will accommodate runner beans (12 plants/wigwam, OH's non-negotiable crop), 3 courgette plants planted with companion cornflowers for better pollination, beetroot, and maybe tomatoes.

Tomatoes: @Lolimac continues to manage her tomatoes from containers, although there is much watering, or so I read. My devotion to worthy tomatoes encourages me to think I might do the same, but my love of them pulls me towards letting them have space in the ground. Companion planting with basil also being considered, in tandem with essential windowsill basil cultivation.

So these are weighty matters in my mind: how densely to plant for maximum yumminess. Patch can be enlarged, but the question of by how much will need answer for next year; meanwhile, containers.