Here are pictures of a vegetable garden in a 100 sq. ft sand box, a SpritzWiz intermittent pulse valve to run four micro-sprinklers , and Osmocote® slow release fertilizer sprinkled on top.
The sand does seem to leach out fairly quickly though. I had mistakenly been using water from my water softener and realized that I was getting too much salt. I turned off the water softener and flushed out the sand ... and it was OK.
Sorry .I keep coming up with new questions. What would you think would be a reasonable period of time for a slow release fertilizer for the vegetative state? And then use a different fertilizer for the flowering state how long for that.
Maybe also here is another idea.
Use different beds for the two different growing phases. Sort of like an assembly line. I have been scooping my vegetables out of my sand completely intact with all their beautiful roots. I think it should be easy enough to remove the plants from the first sand bed and then plop them into a second sand bed that is already going strong with the flowering type fertilizer. Intermittent sprinkling would reduce the shock of the change.