So, you're already convinced that square foot gardening is the way to go and you've made your plan, now you can get to work!
Assemble all of your materials and tools before you begin building. You'll need the wood to construct the boxes, galvanized (or something equivalent) wood screws at least 3 inches long, weed cloth to attach to the bottom of the box, and staples or roofing nails. As far as tools, you'll need a drill, a circular saw (if you don't have one, the lumber yard should be able to cut your wood for you for free), a staple gun or hammer to attach the weed cloth, and a razor knife or scissors.
When making your shopping list for materials, keep in mind that lumber comes in 8-foot lengths and multiples of two thereafter (8', 10', 12', etc.). After you know the size of your box, you can figure out what length to purchase and cut into pieces to make your box. For example for a 4'x4' box, you can buy two 8' pieces and cut them in half to make the 4'x4'. For our 8'x2' box, we bought two 10-foot long pieces and cut them to make the 8'x2'. You get the picture...
You only need to fill your box 6" deep with soil, unless you're growing carrots or other longer root vegetables, in which case you can make a smaller box that is 12" deep. People are pretty skeptical about the six inch deep boxes, and I was too last year before we started. I worried that it just wouldn't be deep enough, especially for our beets, but we had perfect results. There's no need to go deeper than needed, and because the soil is kind of pricey, you don't want to use more than you need. We built one box that is 2'x2' and 12" deep for carrots and the rest of our boxes are 6" deep.
As far as the type of wood, you can use any type as long as it isn't treated. Treated wood is pressure soaked in formaldehyde (yuck!) and will leach chemicals into your soil, and you don't want that.
Here are the materials we bought for one 4'x4' box:
Two - 2'x8"x8' pine boards
$8 in New Mexico, but the cost of wood will vary depending on where you are located.
12 galvanized wood screws, 3.5" long (this is what we already had on hand)
About $15 for a box, which will be more than plenty. If you don't use this kind of thing regularly and don't want extras, you can just buy what you need at any good hardware store and pay by the pound.
One roll of natural weed cloth
$15 for a roll that is 40"x36'. We used what we had leftover from last year. A roll will be more than plenty so you can use the extra for future projects.
About 24 roofing nails
$3 for a box or buy what you need by the pound. We used the staple gun last year, but it is at the cabin and we didn't want to buy another one so we used roofing nails. They worked just as well as the staples.
Total: $42 for one 4'x4' box, but keep in mind that all of the materials except for the wood can be used again for future boxes or other projects. I've seen packages at Lowes for raised bed gardens that have all of the wood pre-cut and you just need to assemble it. They are made out of cedar and are only about $50. If you're only making one box or if you don't already have the tools, that may be a good (and easy!) option.
Instructions for building your box:
1. Measure your wood. Do it twice.
2. Using a circular saw, cut the wood into the lengths you need. Hopefully you have a better place than the top of the compost bins to do this...
|Note: please use safety precautions. Here you have what not to do...|
3. Optional: We bought 8" tall boards so that we'd have some space between the top of the soil and the top of the box (soil is only 6" deep). We used the table saw to cut a groove marking 6" so we would know how deep to fill the soil. If you don't have a table saw, you could probably just draw the 6" mark.
4. Assemble all of your materials and tools on a hard surface.
5. Begin with one corner of the box. Line the corners up so the wood is overlapping and drill in three screws per corner. Rotate the box and continue drilling the corners until the box is completed.
6. Turn the box upside down and roll out the weed cloth. Hold it tightly and staple or nail cloth along the edges. I used about 6 staples/nails per 4' side. Depending on the dimensions of your roll of cloth, you'll probably need to attach two pieces. It is ok if they overlap. Cut away excess cloth with a razor knife or scissor.
7. Carry the box to its location. Make sure you put it where you want it because once the soil is added, it is really difficult to move it and the weed cloth will probably tear.
Voila! You have your box, and now it is ready to be fill with Mel's mix. You still need to install the grid, but that is easier once the soil has been added.