I make sure they get a steady supply of water.

I topped off the bed with about 6 inches of compost (made from mesquite chips, leaves and beans, the fuel pellets we use for kitty litter, kitchen scraps and lawn clippings)

I applied soil sulfur liberally and a small amount of ammonium sulfate before planting the seeds.

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That's it for them.

You don't list what city/area you live in on Your Page so I will infer from the hot comment that it is Phoenix area, Tucson or Yuma.

Assuming you used your soil for the garden bed it will be lacking in nitrogen and carbon and little else. IMHO no further supplementation is needed beyond adding a scoop or two of finished compost mixed into the planting hole between plantings and occasionally around any annuals that decide to grow into year 2 and longer. Hence the importance of maintaining a compost pile to make your garden produce even more cost effective.

Anything else is a waste of money. The fish fertilizer ($$$$!!!!) is a great source of slow release nitrogen. As per the directions telling you to divide it up and add more often in hotter areas---nitrogen is volatile and will gas off so it needs to be replaced. The hotter the faster it evaporates.

If you choose to continue fertilizing figure out the total amount likely to be added the entire season for that plant(s) divide the amount to add it in smaller amounts more frequently weekly or every other week. Keep in mind as well that some plants fertilizer should be discontinued at some point, others increased both to maximize yield. I get you want organic. Ammonium sulfate is a pure product, cheap and works well, especially if mixed into water. Just sayin.

Over fertilizing or fertilizing past a point can be worse than under fertilizing. It can push vegetative growth instead of fruiting, increase pests.

http://ag.arizona.edu/pubs/garden/az1020.pdf
http://cals.arizona.edu/pubs/garden/az1005.pdf

A good layer of organic mulch built up as the plants grow up (so you don't initially block them out or damage them) will preserve moisture, block weeds and cool the soil slowing nitrogen off gassing. Additionally the decomposition of the mulch while initially depriving the first inch of soil of nitrogen used to decompose the mulch the breakdown material will then release available nitrogen and carbon into the soil.

Adding powdered soil sulfur is a good suggestion too to try and keep the pH as near neutral as possible.

If those are small radishes consider growing them in trays. They produce so fast it is kind of a shame to take up space in a garden.

Be sure to get a paper plate under each of the melons if they are not kept off the ground.

Here is a link that might be useful: Ten Steps to a Successful Vegetable Garden

The radishes are 2 feet from the watermelons so I figured they would be done and eaten before the watermelon took up that needed space.

I'm curious to what you grow each spring season?

Thanks!