V. Puustjärvi
What are the fundamental factors governing the cultivation of pot plants? They are light, temperature, free circulation of air and growing-medium, which if well aerated is easily penetrated by roots, contains plenty of easily available water, provides an adequate and balanced supply of nutrients and is free from organisms and substances harmful to the growth. These factors are the same for all plants, whether grown in beds or pots.

There is one very essential difference between the pot and bed culture. In bed culture, the area of the leaf cover and growing-medium are of the same size. In pot culture on the contrary, the area of the leaf cover may be manifold compared to the area of the growing-medium. Pot culture sets, due to this, great claims on the growing-medium. The roots have to absorb large amounts of water, nutrients and oxygen from a small volume of growing-medium. Let us imagine for example a 5" pot, where the volume of the growing-medium is 0. 64 1. The diameter of the leaf cover of the plant in the pot may easily be about 20 cm, and the area over 300 sq. cm. For every sq. cm of the plant cover the volume of the growing-medium will be only 2 ml. If the thickness of the growing-medium in bed culture is 20 cm, the corresponding volume would be 20 ml, i. e. ten times more. The plants water requirement, however, is in both cases the same, because the water requirement is determined by the solar radiation reaching the leaf cover. This, therefore, means that the plant has to take 10 times more water from a pot than from the same volume in bed culture.

In the light of the facts stated above it is easy to understand that in pot culture a special attention has to be paid to the water economy of the medium. Another fact to be considered is the oxygen economy of the medium. Without sufficient aeration the roots are not able to take up the large amounts of water required by the plants, although the medium would contain it sufficiently. So, an ideal growing-medium should be as follows:

  1. Pore volume should be as high as possible.
  2. It should be possible to divide the pore volume between water and air in such a way that it corresponds to the requirements of the plants. Evidently in this case the general rule, that the water and air spaces should be equal, is valid.
  3. Water in growing-medium must be easily available. It means that the suction force of the medium must be as low as possible.

Moss peat fills all the aforementioned claims rather well:

  1. The pore volume of moss peat varies from 94 to 97 volume-%.
  2. By changing the structure of peat moss, the pore volume can be divided in a wanted way between water and air. It is easy to achieve a
Puustjärvi, V. (1973). MOSS PEAT AS POTTING-SOIL. Acta Hortic. 31, 161-162
DOI: 10.17660/ActaHortic.1973.31.22

Acta Horticulturae