The simplest solution is to lay out drip line or drip tape (emitters every 6 or 12 inches) along rows. The problem with that simple approach is that every row gets watered together, and say, the tomato must get water if the lettuce needs it. Dividing the garden into zones, and watering plants with equal needs at the same time can help. A valve for each zone can adjust the flow to the zone. Or you can use more than one timer.

The ultimate adjustable setup would be an adjustable emitter for every square, but that would be crazy complex in the wiring, with 56 emitters.

A hybrid approach would be tape for small crops and adjustable emitters for big plants.

That is one of the common problems with Sq Foot Gardening - watering.

Everything with totally different water needs is so close together that Mel designed it for hand watering plants individually, not auto or whole bed systems. Of course with such small beds hand watering is easy to do and really works best for the plants. Same with nutrient supplements - different plants have different needs.

Why not post this over on the Sq Foot Gardening forum for suggestions from the folks who practice it. They may have figured out alternatives to watering by hand.

Otherwise, as John said above, the only alternative is very careful zone planting, lots of different shut off valves along the system, and a whole range of various GPH drippers.

Dave