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The walls of the root hairs are permeable, that is to say, water molecules are able to pass through them. The fluid inside the cells of the root hairs is packed with a high concentration of nutrients in the form of mineral salts, while the water on the outside contains a much lower concentration. In order to balance the two, water passes from the moist soil through the cell walls and into the root hairs, in effect, causing the dilution of the concentration contained within the root. As the water passes through the cell wall it carries along with it the nutrients it is holding in solution.

If the concentration of nutrients in the soil is higher than that within the roots e.g. if you have given your tree more than the recommended dose of fertilizer, water will pass from the roots back into the soil and the roots will die of dehydration. This is what gardeners call ‘root burn’, and it explains why smart gardeners allow farmyard manure to stand and rot for about a year, before applying it to the soil.

The thicker roots act as winter storage vessels for sugars that the leaves have produced during the summer months. The sugars are passed down to the roots for storage in late summer and remain there until the buds begin to swell in the following spring. At this point, the fine roots begin to take on water to pump into the swelling buds. As the water is passed upwards through the roots and into the trunk, it facilitates the growth of new shoots and leaves. Once they are properly established, the new leaves are able to support themselves fully and the same cycle begins all over again.

These nebari, or thick roots, anchor the tree in the soil and act as pantries for the plants by storing sugars over the winter months.