The best way to use the Plant Booster system for plants in along planter is to set up a series of individual pots, each on their own Plant Booster control device.  As they grow, the foliage all blends and it looks like one long plant.  This way all the plants are individually watered and you can be 100% sure that they will all be watered correctly.
The picture below includes three pots in a 3ft long cedar planter box.