Step 1: Materials
A poly-boy is a 1m x 1m x 1m plastic cube with a reinforcing cages around it. It is used in industry to hold and transport 1000L quantities of liquids. I removed the plastic insert and just took the cages.
You also might need:
Castors (if you want to move it)
Some outdoor fabric (I used outdoor umbrellas I found on the side of the road)
Dirt & plants
Step 2: Give it Some Wheels
The castors I used are a little small for the weight of the garden, I would recommend assuming the soil will weight the same as water (1 cubic centimeter of water = 1 mL = 1 gram).
To get the weight, measure the volume (length x width x height) of the soil in cm and divide it by 1000 to get the weight in kilograms AND the volume in Litres. Soil and compost are sold in litres so this is a handy number to have. Don't forget to divide this weight by the number of wheels to get the weight on each wheel.
If you are in an Imperial country, measure the volume in inches (length x width x height) and multiply by 0.03606 to give you the weight in pounds (lb). As to the volume - I'm sorry, I'm an engineer and even I find it confusing to use inches, pounds and gallons!
Step 3: Cut the Wood for the Base
I used a circular saw to cut a series of lines at the same depth as close together as I could. It was then easy to just knock out the slivers of wood with a hammer.
I did this to ensure the wood couldn't slide out - but in hindsight this is not strictly necessary.
Step 4: Chuck It All Together
Place a couple of notched sleepers (or simply pieces of scrap wood) through the cage to support the soil.
Step 5: Line It!
I did not add any drainage holes - I assumed that there would be enough gaps between the plastic bags to allow excess water to drip through.
Step 6: A Load of B.S.
Step 7: The Fun Part
Plant your plants - Look up some of the great Square-Foot Gardening Instructables to get the most out of your plot.
Mulch - It's quite important for weed suppression, water retention and insulation for your plants.
And most importantly, enjoy it!
Extra Ideas to Try:I would like to cut holes in the side of the fabric and plant creeping & climbing plants which can climb around the outside without disturbing the top plants.
If you are in a cold climate, you could try enclosing this in the winter as a sessional green house.Have a look on Instructables, there are hundreds of space saving plant ideas.
Good luck and add any ideas you think might be interesting!
Step 8: Update!
If this works, when the carrots are ready for harvest, I will replace them with something creeping like tomatoes and cucumbers as we come into spring!