POTTING COMPOSTS

Wairarapa Times-Age, 15 September 1938, Page 4

POTTING COMPOSTS

COMPONENTS AND BLENDING. Very elaborate and complicated mixtures of potting composts, such as were beloved of the early part of last century, are held in slight regard today, and we readily agree that simpler mixtures grow most things very well. Loam, leaf mould, peat, and sand are the plantsman’s chief requirements, maybe with additions of small quantities of organic or chemical fertilisers, which are varied in accordance with the particular plants to be potted.

Nevertheless, we see numerous instances where too little regard is shown to the selection and mixing of ingre* dients of composts which are to be the sole root-run of plants from which much is demanded. The common custom seems to be to recommend certain proportions of loam, leaf mould and sand, disregarding the fact that so much depends upon the character of the loam and leaf mould, whether those proportions should be varied, and whether much or little sand will be beneficial or the reverse. Sand, in the clean sharp condition required for potting purposes, provides no nourishment for plants. Its sole utility is to prevent the loam and leaf mould binding down to a compressed mass, excluding air and impeding the passage of water. Deficiency of sand will soon result in waterlogging and souring of the soil to the serious detriment of the health of the plant, but an excess of it will soon prove injurious, for two reasons. First, it will facilitate too rapid passage of water, necessitating continuous use of the water can to keep the plants from drooping; secondly, the pot space occupied by the sand reduces the bulk of soil which is capable of holding water and nourishment for the plant. It needs to be realised that loam varies tremendously in weight and texture. That which comes originally from a pasture on heavy, retentive soil will tend to bind and compress far more readily than the turf of a shallow, sandy soil. Some loam is almost entirely root fibre and decomposed grass blades. Material of that spongy, porous nature requires little or no addition of sand, but that from strong yellow clay soil may require double the quantity ordinarily required.

Much that passes under the name of leaf mould is too sour, and infested with spores or fungi to be really good for potting. Sweet, properly-made leaf mould of oak or beech leaves is good, wholesome, and helpful, especially to soft, young plants, which are required to make luxuriant growth in a short time. For plants of hard, woody nature and slow growth, good brown woodland peat is to be preferred to leaf mould. It is more fibrous, and, as it resists decomposition for a long time, it suits plants which occupy their pots for a year or two instead of two or three months. We place almost as much importance upon mixing compost well in advance of using it as upon selection of ingredients, particularly so if the mixture is to contain manures, fertilisers, or sweetening agents, such as charcoal or lime. Even loam and leaf mould or peat, when blended together, will immediately start a process of change of character. Bacteria and chemical contents of the different parts of the compost set to work to speed up the subtle, but important, changes, and until a good deal of their labour is accomplished, the condition of the soil in a pot is not conducive to formation and activity of new roots.