Why are the leaves turning yellow?

Here is a look at the garden today.

Allot of the plants are turning Yellow. So I applied some Epsom salts around them to see if this will green them up a bit. I found that to much or to little water can be the cause of the yellow leafs. Also temperature change . We have had too much water the last week or so. And temps up and down. Also this could be a lack of nitrogen or iron. As to much rain could have washed all the minerals or nutrients out of the soil. You may click on photos to enlarge.

The bottom photo is 2 days later. The new growth is greener.
After the Epsom salts. We have had 2 more inches of rain though.

These 2 photos are melons and cukes

You may ask why the clover is in the above photo. It is a good source of nitrogen so I let it grow freely and pull it to add to the soil.

The new pepper plans are looking well so far.

The Lunar planting calendar for this month is located at the bottom of the page.