Non-Standard Size Grow-Box – Filling and Fertilizing

Q. I have built 2- 4’X4′ grow boxes that are 10″ deep. I purchased
on the Food for Everyone website 2 8 oz.packages of the micronutients. For 1 package I plan to mix my weekly feed ( w/ 3 lbs epsom salts and 1- 20lb. bag of 16-16-16.

My plan was to use the other micronutrient package for the preplant mix (mixing with gypsom,epsom and Borax)

Question #1- For the preplant mix, how much gypsom, epsom salts and Borax should I mix in to place in each each box? I am not
mathematically inclined, so any help on figuring out the measurements is VERY appreciated.

Question #2- Am I okay to use the micronutrients package for the
preplant mix, or is that just for weekly feed?

Question #3 I plan on using 1/2 Blowsand and 1/2 Peatmoss as my filler- how much should I buy to fill both boxes?

A. Ten inch-deep boxes are fine. However, they use more materials than necessary and don’t grow any better crops than 8″ boxes. We recommend boxes that are 8″ deep (actually 7 1/2″ is the standard size you will get at the lumber store).

Do NOT use the micro-nutrients in your Pre-Plant mix. It is unnecessary, wasteful, and might even be bad for the plants. The Micro’s are only to be used to create the Weekly Feed Mix.

Remember in mixing the Pre-Plant to use 80 parts lime or gypsum, 4 parts magnesium sulfate, and 1 part 20 Mule Team Borax.

The amount of Pre-Plant you need to use in a 4′-long X 4′ wide box is 2 ounces per running foot (1 ounce per running foot in an 18″-wide box).

1. On the soil underneath the box spread 8 ounces (that’s 2 ounces per running foot).

2. Mix another 8 ounces of Pre-Plant with the soil mix at the same time as or immediately after you fill the box and before you plant. And at the same time mix 4 ounces of Weekly Feed into the soil mix.

You will need 13.33 cubic feet of material in total. You will have a better mix if you use less sand, and add some Perlite. I recommend you use 50% peat moss (or sawdust – preferred) 15% Perlite, and 35% sand.