Whilst I do not have the weighed volume of potatoes that I am growing, yet, (I will have, and will post them when I have them), it is now obvious that growing potatoes in tyres is much more productive than just growing them in a bed. I'm only up to tyre 4; hopefully I'll get to tyre 6!
To create a potato tower: Have a ready supply of tyres (or tee up your local garage to save you some when you need them); Place the tyre on the ground, or concrete, brickworks, pavers - doesn't matter. Add half a tyre of soil; place 3 seed potatoes in each tyre. Cover with soil and water in. When the shoots appear, add another tyre and fill around the foliage with lucerne hay or straw. Pea straw might also work, although it is expensive. When the shoots are level with the second tyre, fill in with hay or straw. Place another tyre on top and fill again; When the shoots are level with that tyre, place another tyre on top and fill the spaces with hay or straw. Keep going until you have about a 6-tyre tower. When the plant starts to flower, remove the top 2 tyres and 'bandicoot' - this means, digging for small new potatoes. (don't forget to weigh your crop and keep a record!). You'll find lovely, CLEAN, potatoes in this straw. 'New' potatoes can't be bought - let me tell you - new potatoes have a taste all of their own and are astronomically gorgeous!!
Don't forget to water your potatoes regularly. If you are going away, invest in orange plastic inserts for bottles that you'll find in any gardening section, and put in a bottle per tower. The bottles will slowly drip the water into the spuds whilst you're away.
Leave your potatoes in the ground and only dig them up when you need them. They will be protected in the ground which can now be called 'a root cellar'.[You'll only need your hands, not a shovel!] You'll now need to protect them from rain, so they can be covered with a small tarp.
Click on photo to better view the towers; download 'garden' to see the potato flowers.