The whole benefit of square foot gardening arises from the use of a rigid grid to divide the garden up. The grid is a positive control on the way you will work your garden and plant your seeds.
Step 1 – Decide the Size
Decide on the size of the grids. They will need to fit exactly into or onto the garden boxes you are going to use. Probably the largest will divide a four feet square garden box into sixteen one foot squares. The smallest you will use will divide a two feet square garden box into four one foot squares.
Step 2 – Decide on the Material
It is important that the grids are strong. They should last as long as the garden box. Ideal materials are wood lath or narrow bore plastic piping. In reality, any rigid material will do but make sure that it does not contain any paints, stains or varnishes that could be hazardous to your plants. Although you won’t be doing heavy digging work in your box gardens, you will be actively gardening, so the grids also need to be rigid enough to stay in place
Although it might seem an attractive option, avoid the use of rope and string. These materials will start off reasonably well, but will soon stretch out of position and cause the garden design to fail.
Step 3 – Set up the Grid
Setting up the grid is very simple. All you need to do is cut the material into the correct lengths (the length of one side of the garden box) and arrange them to make a grid of 90º intersections with each intersection one foot away from the next. It isn’t necessary to have an outside edge to the grid – that will be provided by the garden box.
Step 4 – Fix the Grid
The grid needs to be secured at each intersection. Any form of fastener will do, although small nuts and bolts with wide washers offer a stronger join. The materials you are using are narrow, so it will be safer to drill the holes for the fasteners. The joints do not need to be particularly tight, but they do need to be secure. Once the grid is attached to or placed in the garden box it will be held rigid by the box.
Step 5 – Fit the Grid
Fit the grid into the garden box or onto the top edges. The neatest and most convenient position is to have the grid resting on top of the soil mixture. This will prevent plants damaging themselves against the grid in windy conditions. Having the grid resting on the soil mixture will also make working in the box easier.
Grids resting on the soil can be removed at convenient times to be cleaned and check for damage.