Science and Experiments 2011
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 tubers (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 3 or more inches above the surface, and not earthed up until this time, then the conversion to a shaw cannot be reversed.
The photographs below describe the experiments conducted in 2011.
This shows the experimental growing station. The earth is contained between two sheets of glass about two inches apart. Boards on the sides keep the soil dark. The chamber was divided into four sections, divided from each other by wooden slats. The four labels pinned to each section are labeled, from the left, "Earth up immediately", "Earth up at 1", "Earth up at 2 ", and "No earthing up."
As the earthing up occurred during the growing season, so addition boards were added to the first three section, to keep the stolons and basal roots below the surface in darkness. But it was possible to remove these for a short time to observe how the root system and the potatoes were developing.
This shows the experimental chamber with the boards removed.
The results are shown above. The seed potato on the left, which was "earth up immediately" produced potatoes all the way up to the eventual soil surface. (NB the seed potatoes were planted at the bottom and the original soil surface was approximately at the level of the top of the label on the right. The second chamber, labelled, "earth up at 1 in" produced potatoes above the original soil surface but not as high up as the "earth up immediately chamber." The third chamber labelled "earth up at 2 in" produced potatoes to a slightly lower height, and the last chamber, labelled "No eathing up" produced all its potatoes near the bottom.
The initial conclusion from this experiment is that the sooner one can earth up the better. As soon as the stolon appear, earth up to a depth of maybe 2-3 inches. This means that the roots remain roots, and so are capable of producing stolons, where potatoes come from and do not convert to shaws.
However, earthing up in this way means that the potato plant cannot form leaves and so cannot get energy from photosynthesis. So ideally one wants a way of allowing some of the roots to convert to shaws as soon as possible so that the plant can derive energy for growing, while other roots can be earthed up as soon as the appear at the soil surface so that more potatoes are able to grow above the original level of the soil surface.
This is precisely the point of the Henley Potato Tower - it has holes in the sides so that some of the roots may be encouraged to grow through these holes and so to develop into shaws on the outside of the tower, while others may be earthed up on the inside of the tower.
The photographs below show the harvesting of a four-er in early September
However, as the soil was brushed away after the bottom layer of the tower was removed, so the number and size of the potatoes that appeared increased markedly. In particular, there was a huge grouping of potatoes, much larger than others elsewhere in the tower, which had all been fed by the huge shaw which grew through the hole at level 1 of the tower.
The harvesting of a two-er. Variety Lady Balfour: Planting date Mid May. Harvesting date early September.
With shaws removed. First level of three level tower beneath ground level.
63 potatoes, plus some tiddlers from two seed potatoes.
Total weight: 4,874 grams, from two seed potatoes.
Video of the harvesting of a Henley Potato Tower