joannaqcw, the greatest advantage of a drip irrigation system is that it puts the water where it will be best used - at or near the roots of the plant. Ideally, the emitters will coincide with the spacing of the plant. As the root system grows larger, more water will be needed and this is accommodated by the length of time that the system is allowed to operate. One can determine this by checking the wet patch of soil around each plant. At first only a small area needs to be kept wet but as the roots grow out, a larger wet area would be needed. In a perfect state of affairs, at maturity, the roots of all the plants will occupy all the area (if not the volume) of the planted bed and the irrigation will be operated at its longest duration (even full time). All the listed plants will need adequate water for establishment but as time goes on, I imgine that the asparagus and beans will need more water than the onions and potatoes.