Potatoes grow from seed potatoes which put out shoots which develop into large main roots. Under the soil other roots, known as stolons, branch off from these main roots and potatoes form at the end of these stolons and sometimes at nodes which form along their length. The main roots grow upwards through the soil and eventually reach the soil surface. If they are allowed to continue to grow upwards into the air and the light, they change into shaws which produce leaves. Research has shown that if the emerging stolon is covered in earth, the conversion to a shaw will not occur and the stolon continues to grow upwards and continues to produce branches and nodes from which potatoes may grow. However, if the stolon is left until it is three or more inches above the surface then it will convert into a shaw, an irreversible process, and the potato plant from this height and above will not produce potatoes.
However if all roots were covered in earth each time they emerged the plant would never be able to produce leaves and, the energy within the seed potato being finite, the plant would run out of energy and so die without producing a single potato. The whole point of the Henley Potato Tower is that it enables one to train some of the early emerging roots through the side of the tower into the air and light. They then produce leaves which bring energy into the plant. Meanwhile the roots inside the tower are still under the earth and have energy to grow upwards enabling them to produce more potatoes throughout the tower.
Earthing up Experiment
According to the science earthing up regularly is key to the success of a tower. To prove this we did an experiment. We grew four potato plants in identical conditions. We then earthed up one plant immediately, one plant when it was one inch above the ground, one plant when it was two inches above ground and didn’t earth up the other at all. The final level was the same in sections one, two and three. The results are recorded below:
|Experimental rig|| Results from left to right:
The purpose of this experiment was to show that by earthing up it is possible to produce potatoes all the way up a tower. It is clear that earthing up allows potatoes to grow a long way above the height of the original soil level. Earthing up works and the less time the emerging shoot has in the light before you earth up the better.
However in this experiment all emerging shoots were covered in earth and so no leaves were produced until the earthing up was complete, which was very late in the season. This meant that although potatoes were produced throughout the tower when the plants were earthed up frequently, there were not more potatoes and they weren’t significantly larger.
The whole point of a Henley Potato Tower is that it has holes in the sides so that some of the roots can be trained through these holes and develop into leaves while others can remain within the tower and continue to grow potatoes.
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