The proper amount of space often depends on the growing method, but I like to use biointensive plant spacing for a more manageable and productive vegetable garden.
With a standard 4-foot-wide bed, you can easily reach the center, so planting intensively means you can plant in all directions and still be able to harvest.
Vegetable / Spacing (Inches) / Spacing (Centimeters)
Amaranth / 6 in / 15 cm
Asparagus / 12 in / 30 cm
Artichokes / 24-36 in / 61-91 cm
Arugula / 4-6 in / 10-15 cm
Basil / 12-18 in / 30-46 cm
Beans, bush / 3-4 in / 8-10 cm