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Potting mix [ Horticulture ]
Synonym: Potting med
ium or Potting mix or Growing substrate or  Container compost etc..

Dictionary of botanic terminology
index of names

  A potting medium is a mixture of various raw materials designed to be used in horticulture as a substrate to support the roots of plants cultivated in pots and containers.  

A good container compost should offer the plant a substratum for both stability, a high water capacity, good nutrients supply and a sufficient air space for ample root respiration allowing water and nutrient uptake. The balance of these needs will vary, however, depending on the plant being grown and the stage of growth. When a substrate is saturate of water most of the air is drove out. If it is too dense, without air, roots suffocate and lead to rot, otherwise a soil that is too porous, will dry out too rapidly and the plant either has to be watered daily or suffer the consequences of desiccation.
Potting mixes resolve problem combining different ingredients with opposite qualities, some that holds water and other that keeps the mix open and light. But usually container media in horticulture serves primarily as mechanical support for the plant. They have only small reservoirs of water supply and short substrate columns that affect drainage of water
The trend in conventional gardening for many years has been the increased use of soil-less media. A major reason for this has been concern about soil-borne plant diseases and the excessive density of mixes where soil is a dominant ingredient. However, soil is still used in some organic blends.
There is no single perfect potting soil. If one works for you, then it works for you. Experiment! Working from tried-and-true recipes is a good idea, especially at the beginning, don’t be frightened to experiment with different blends for different plants. When experimenting, begin by making small batches and give them a thorough evaluation.

Potting soil for cactus and succulents:
Known the ample variety of cactus and succulent plants, there is no one perfect formula for potting soil, but the majority of these plants are rather tolerant.
The major characteristics to look for are good drainage and aeration, for the reason that standing water and a insufficiency of air circulation in the substratum easily make rotting the root.
A suitable potting soil must have superior drainage - a traditional potting soil will retain some moisture between watering thus increasing the chance of root rot and should not have a large amount of organic matter such as peat, compost, manure. High columnar specimens should be planted in a potting substrate that is firm as much as necessary to prevent them from tumbling. coarse sand or gravel may help to increase the soil compactness. The medium should be slightly acid, with a pH of 5.5 to 6.5.
Most commercial potting mixes for cactus and succulent available on sale contain too much organic material and have unsatisfactory drainage. It is best to amend them with pumice grit or perlite.

See also: Mineral substrate

Ingredients for culture substrate:






Holdfast roots  [ Botany  ]

Dictionary of botanic terminology - index of names

  Some species of climbing plants develop holdfast roots which help to support the vines on trees, walls, and rocks. By forcing their way into minute pores and crevices, they hold the plant firmly in place.  
Climbing plants, like the poison ivy (Toxicodendron radicans), Boston ivy (Parthenocissus tricuspidata), and trumpet creeper (Campsis radicans),  develop holdfast roots which help to support the vines on trees, walls, and rocks. By forcing their way into minute pores and crevices, they hold the plant firmly in place. Usually the Holdfast roots die at the end of the first season, but in some species they are perennial. In the tropics some of the large climbing plants have hold-fast roots by which they attach themselves, and long, cord-like roots that extend downward through the air and may lengthen and branch for several years until they strike the soil and become absorbent roots.

Major references and further lectures:
1) E. N. Transeau “General Botany” Discovery Publishing House, 1994




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