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 and the potato plant from this height and above will not produce potatoes.
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 results are recorded below:
|Experimental rig|| Results from left to right:
It is clear that earthing up allows more potatoes to grow and to grow a long way above the height of the original soil level. Earthing up works and the more frequently you earth up the better.
However earthing up like in this experiment means that there is a poor leaf / potato ratio and so the plat cannot get enough energy through photosynthesis to allow the potatoes to grow large.
This is precisely the point of a Henley Potato Tower. It has holes on the sides so that some of the roots can be trained through and develop into leaves while others can remain within the tower and continue to grow potatoes.