Soil Needs for Filling My First Square Foot Garden

Apparently soil used in a square foot garden needs to be quite specific in its blend if success is to assured.  Mel, from the Square Foot Gardening Foundation gives this recipe he has used with fantastic results:

Total Soil Needed for 4' x 4' x 6" Bed:  8 Cubic Feet

• 1/3 Coarse Grade Vermiculite (Palmetto Vermiculite in SC)
• 1/3 Sphagnum Peat Moss (bag is compressed, when opened it about doubles)
• 1/3 Blended Compost (a variety of types -- 5 preferred)

From my reading it appears as if the Vermiculite is often hard to find locally and expensive to ship.  They suggest possibly finding it at Commercial Nurseries or swimming pool companies if local home and garden centers do not have it.

Since my first garden is being paid for by birthday and Christmas gifts I am taking the easy route and buying pre-mixed, bagged soil.  Instead of jewelry or lovelies of some sort I will request dirt!  Both Lowes and Home Depot have it listed on their websites, but it is not yet in stock in the stores (shipping from HD is $10 a bag and Lowes does not ship it).  I am hoping my local Lowes will stock it soon.

• Garden Time 32-Quart Organic Potting Soil from Lowes
• Nature's Way 1.5 cu. ft. Square Foot Gardening Potting Soil Mix from Home Depot

Both of these are the exact mix developed by Mel Bartholomew (they even have his image on the bag).

Soil upkeep from year to year is simply to add homemade compost.