Watermelons, cukes, and cantaloupes

I have about 1000 sf where I have pine trees about every ten feet in rows. A bubbler is run to each, as well as a couple are out there for trees that didn't make it. The soil is sand just like the beach, with the exception of lava rocks every two or three feet, some the size of cantaloupes, some the size of large Xerox copiers.
I got some big metal rings that surround the trees at the base. I put a stall manure mix in there, as it was free.
Now I want to plant melons and cukes. Do you think it would be better to plant in the rings in the enriched soil, or to till in some peat moss and potting soil next to the rings where the water runs out, and wets the soil? I have heard that melons grow in sandy soil, but I find it hard to believe these will do well without any amendments or fertilizer, as the virgin soil has very little organic matter in it.
I have one place where two trees didn't make it, and I have two water spouts about 10' apart. I'm thinking of making a big rock circle around it, and tilling in good soil down to about a foot deep, plus 6" high above grade. Do melons need that much dirt to root in?
Can anyone with melon growing experience help me out?
Steve
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SteveB wrote:

They are heavy feeders and subject to wilting on hot days if the soil doesn't hold enough moisture so i would not bother planting into just sand as it will serve neither purpose.

They send out long strong roots looking for nutrients and water. Depending on cultivar they can be yards long.
David
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Then you have like ten tiny seedlings.
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