If you grow potatoes in open soil then you need to build up a mound of earth around the plant as it grows. When growing potatoes in tyres or containers the earthing-up process is aided by the containment.
There follows a description of an experiment in potato growing in tyres.
1) In this photo we see a piece of cleared earth with cardboard placed on top of the soil to keep the weeds down.
2) The tyre is fully filled with compost. Make sure that the inside of the tyre rim is filled too so that there is plenty of compost for the tubers to grow in. Press a seed potato into the compost to a depth of four inches or so. Cover the seed with compost and then water.
3) When the plant has grown to about 10 inches (25 cms) tall place a second tyre over the first and earth up, again making sure that the rim is filled too.
4) Three or four tyres will be needed for the plant to fully develop and yield a good crop of potatoes. You don't need to earth up with your best compost, almost anything will do. I use compost that hasn't yet fully rotted down, grass clippings, weeds that have been semi-rotted in a black plastic bag, old tea bags. Earthing up uses a lot of matter and you will soon use up compost that could be used elsewhere.
At harvest time just kick over the tyres and separate them to reveal the crop. Make sure all the compost (including any stuck in the rims) is removed to where it can be used to grow a different crop the following season. Use new compost to grow next year's potatoes.
During this experiment some problems were noted.
- Ordinary car tyres are quite small and make gaining access to the plant stems difficult. Often, stems are damaged when rearranging stems following earthing-up.
- There is much written about contamination from the materials used to construct tyres. Toxic heavy metals are used in tyre manufacture and may leech into the soil. One idea is to just use tyres as a holder, for a plastic sack, in which the potatoes grow. However, that would leave less room for the plant as the inside of the tyre rims are not being utilised.
- Overall, car tyres are probably too small for potato growing. A larger container, such as a 55-gallon blue plastic barrel cut in half (with drainage holes drilled in the bottom), is probably better suited to the task.
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