Question on Soil for 15 plants

I am going to be growing roughly 10 AK47, and 5 White Widows... I've done some research but some parts are unclear which is why i am making this post. I dug a 4x4ft hole yesterday to see how the texture is of the ground at the spot. It is near a water source. I would say another 2 feet i would be at water table, but it gets a little difficult digging deeper.

My question. Filling 15 wholes that are 4x4 ft with quality soil will be far too expensive. Considering the texture of the ground soil there isn't too bad, what would be the best bet for a mixture to create that can be mixed with some soil that is already there? I understand you can use perlites, peet moss, etc... but can i buy bags of that? I was planning on transporting the plants from their 16 oz cups to a 5g pot of Fox Farm Ocean/Light warrior 50/50 mix, then transport them with that soil into the hole. Hope this makes sense

Also i plan on using chemical Nutes, and watering when needed. Watering will not be a problem. I do however plan on covering around the plants with Mulch. I am just worried the soil will be too dense or something. This is my first grow, thats why i am nervous about which soils to use.

This is super good soil and probably the most cost effective for you https://www.rollitup.org/subcools-old-school-organics/338384-2010-revised-super-soil-recipe.html

Thanks. Is there some calculator i can use to determine how many bags i would need, and would it be okay to mix with some of the ground soil there. Might be hard transporting all of those bags. Harvest moon interests me, I will take a few minutes to try to locate some dealers around here.

if your in the mountains thats some good soil already years and years of dead leaves etc. maybe just ad perlite to airiate it a little but then again i dont know were your growing. good luck.

It seems like most of the other spots i have to grow are like sugar sand. It isn't too dry though, it seems somewhat moist. I purchased Mulch and peat moss to help retain moisture. I dont think water is going to be a issue. I've looked around, it looks like i need to get Fish bone meal, Bat guano, and blood meal. It is still a good to mix chemicals with Mg, P, and N and other trace elements even though the soil contains it? I do not want to burn the plants

I would fill it in with pea gravel and use pots for optimal drainage. Unless you plan on growing trees

From what i read i would get a much better yield planting into the ground. Im going to transfer them out of the 5G pots directly into the ground that way they do get a bit bigger. I just want to make sure the soil is right for bigger buds, just way confused on mixing all of these items together and such.I can see the point about the pea gravel... but holy crap just taking back several bags of mulch kicked my ass today!

Here's a more straight forward question. Lets say i end up digging 3x3 ft holes. enough for each plant. I want to use 50-60% of the original ground soil, and the rest my own i purchase.I was looking at Fox Farm Ocean Forrest. I noticed the bags are only 12QT each. It would cost a fortune to do it this way. I have been reading around i am just way confused on how much i need to buy to make sure i make enough mixture. I'm also a little confused on what i need to buy. I understand i need the fish bone meal, blood meal, bat guano, and a bottle of trace elements, but i dont know how much i will need for each hole. I know a lot of soils expand when you add water. This is difficult!

Get some potting soil with a peat base, thin it out with coarse perlite, and add your own nutrients into it.
Some recipes:
http://www.420magazine.com/forums/how-grow-marijuana/71774-vics-super-soil-recipes-notes.html
http://www.onlinepot.org/grow/goodsoil.htm

I've spend all my time after creating this post doing some reading. A lot of people growing in "Sugar Sand" say they cant believe the yield they get for just planting into it. I am going to still alter the soil but not as much as i did the math and we were talking A LOT of money. I am going to still dig the 3x3 holes, and i am going to add that sugar sand to the mix with the following items.

2 gallons of Fox Farm Soil (Light Warrior/OF 50/50 mix) per hole which comes from the pots the plants are already in. Figured this is less shock.
Since the sand has a mild retention problem, i am going to add Peat Moss to the mix
Perlite equal to 1/3 of the added Peat Moss
Bonemeal for the Phosphorus
Bloodmeal for the Nitrogen
Kelpmeal for the Potassium and Trace Elements
If i can find it, Bat Guano for the Nitrogen ( i believe )
and
Epson Salt

I am going to also use chemical nutrients made by Fox farm. I haven't determined which ones yet as i have not researched that far.

Is there any other nutrients i am missing out in the soil mix? I believe it is very solid