Measure useful harvests
A productive plant is only useful if you eat what it produces. Choose crops based on your kitchen as well as garden performance.
Look for repeated harvest potential
Some leafy crops, herbs and fruiting plants can provide more than one harvest when grown and harvested appropriately.
Use space in more than one direction
Climbing plants can turn vertical space into growing space. Succession planting can also make the same physical area useful at different points in the season.