Once the beds are constructed and set in place, it is time to fill them with Mel’s Mix, the perfect synthetic (and organic) soil mix. Three 4x4 foot boxes require 24 cubic feet of Mel’s Mix to fill them (4 x 4 x 0.5 x 3 = 24). This much Mel’s Mix requires one 4 cubic foot bale of compressed peat moss (expands to 8 cubic feet), two 4 cubic foot bags of coarse vermiculite, and eight 1 cubic foot bags of 5 different kinds of compost.
First you need to locate and assemble the ingredients of Mel’s Mix. Compressed bales of peat moss are available at garden centers and the big box stores. Just as with groceries, the amount of peat moss in a “four” cubic foot bale has shrunk to 3.8 cubic feet. I found that some garden centers still have 4 cubic foot bales, but at a cost of double the big box stores. If you are worried about sustainability, Canadian peat is not threatened, being produced at a rate greater than it is being harvested.
Next, you need to assemble the ingredients for a ”blended” compost. If you do not have your own compost and are planning to purchase it, you should look for at least five different types of quality compost. I found that the cheap bags of “compost” at Lowes contained a disgusting grey sludge (was this sewage sludge?). Be careful to check ingredients since many bags of “compost” contain up to 50% of peat as filler, which will throw off the proportions in the mix. During assembly of the Mel’s Mix, your 5-6 types of compost will have to be blended together to form a balanced compost.
Finally, you need to find a source of coarse vermiculite. Mel prefers vermiculite to perlite, despite it’s cost and availability. Vermiculite has better water retention, appearance, tactile feel, and it doesn’t float to the surface like perlite. You can find vermiculite at garden and agriculture supply stores, greenhouse and hydroponic suppliers (e.g., Worm's Way), and some shipping suppliers (e.g. Uline). When you visit your supplier and don’t find the large 4 cubic foot bags, ask them if they can order it. Try to get the #3 coarse grade rather than the finer “horticultural” grade since it has better water absorption properties.
Once you have your ingredients assembled, spread a large tarp on the ground near your raised beds. Empty the eight bags of compost on the tarp, one or two at a time and blend them together until thoroughly mixed.
Next, pour the vermiculite over the compost. Be careful to wear a dust mask when adding the vermiculite because it is very dusty and you do not want to inhale the dust. And obviously, you do not want to do this on a windy day. It will not only increase the dust problem but may even blow away your expensive vermiculite. Mix the vermiculite and compost until completely blended.
Finally, add the bale of peat moss to the mix. Again, the peat may be dry and very dusty, so wear your dust mask. It may help to mist the mix if you have a hose available. Thoroughly mix all ingredients. Mel’s book says you can do this by picking up a comer of the tarp and rolling the mix over on itself. I calculated the weight of 24 cubic feet of mix at being 300-440 pounds. My son and I were not able to roll the tarp so we used a shovel to mix the ingredients by shoveling from one pile to another.
This is the completed pile of Mel’s Mix for three 4x4 beds. The next step is to transfer it to the raised beds. You are not going to pick up a tarp with 300-400 pounds of mix and carry it to your raised beds, no matter what the book says. I used the blue muck bucket which held enough mix to fill a bed about 2 inches high. You want to add the mix in shallow layers, watering thoroughly between additions. You need the mix to be uniformly moist from bottom to top, so this step is essential.
Here’s a bed filled with the mix. It should but does not come completely up to the top of the box. This is probably because the volumes of the ingredients I used did not really come up to specs. I plan to add additional compost next season and hopefully that will help. In addition. Mel’s Mix tends to settle, so it needs to be stirred up when adding compost before each planting.
Your garden beds are now assembled. The next step is to plant seeds or seedlings and enjoy the results. I have found Square Foot Gardening to be easy (once construction of the beds is done) and very rewarding. My garden plot is neat and virtually weed free and the beds have produced a huge amount of fresh produce this year. I am looking forward to next year, when I will be gardening with all of the experience I gained from this first year.