Hollie Sidon, of Ardgowan School, asks :-

How long do roots from trees grow?

David Burritt, a botanist at Otago University, responded.

The ability of plants to obtain both water and mineral nutrients from the soil is related to their ability to develop a large root system. The annual production of roots by a plant often easily surpasses that of shoots. In trees planted 0.5 m apart the major root systems reach a total length of 12 to 18 km, but if the minor root systems and the root hairs are added to this the length would become considerably greater. Because they are so large the root systems of trees are hard to study, but the roots of smaller plants such as rye have been studied in great detail.

In the 1930s, a scientist called H.J. Dittmer examined the root system of a single winter rye plant after 16 weeks of growth and estimated that the plant had over 1.3 million roots, extending more than 500 km in length and providing 200 square metres of surface area. This plant also had more than a billion root hairs, providing another 300 square metres of surface area. It is also interesting to consider how deep roots can grow down into the soil to reach water. The roots of most annual crop and garden plants usually grow between 0.1 and 2.0 metres in depth, but the roots of some desert dwelling plants may extend down more than 50 metres to reach groundwater.

So just like an iceberg, which has much of its mass hidden beneath the water, many plants have much of theirs hidden beneath the soil.