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  MG Manual Reference
Ch. 9, pp. 10 - 12
[Selecting an Interior Plant: selecting | environmental factors | media ]

Media Top

The potting soil, or media in which a plant grows, must be of good quality. It should be porous for root aeration and drainage, but also capable of water and nutrient retention. Most commercially prepared mixes are termed artificial, which means they contain no soil. High-quality artificial mixes generally contain slow-release fertilizers, which take care of a plant’s nutritional requirements for several months. However, commercial mixes are often misleading as to content, and unsatisfactory for proper plant health. It is better to mix your own if possible.
Preparing Artificial Mixes
Artificial mixtures can be prepared with a minimum of difficulty. Most mixes contain a combination of organic matter, such as peat moss or ground pine bark, and an inorganic material, like washed sand, vermiculite, or perlite. Materials commonly used for indoor plants are the peat-lite mixtures, consisting of peat moss and either vermiculite or perlite. Here are some comments concerning the ingredients for these mixes.
Peat Moss is readily available baled or bagged; sphagnum peat moss is recommended. Such materials as Michigan peat, peat humus, and native peat are usually too decomposed to provide necessary structural and drainage characteristics. Most sphagnum peat moss is acid in reaction, with a pH ranging from 4.0 to 5.0 It usually has a very low fertility level. Do not shred sphagnum peat moss too finely.
Vermiculite is a sterile, lightweight, mica product. When mica is heated to approximately 1800° F, its platelike structure expands. Vermiculite will hold large quantities of air, water, and nutrients needed for plant growth. Its pH is usually in the 6.5 to 7.2 range. Vermiculite is available in four particle sizes. For horticultural mixes, sizes 2 or 3 are generally used. If at all possible, the larger-sized particles should be used, since they give much better soil aeration. Vermiculite is available under a variety of trade names.
Perlite is a sterile material produced by heating volcanic rock to approximately 1800° F. The result is a very lightweight, porous material that is white in color. Its principal value in soil mixtures is aeration. It does not hold water and nutrients as well as vermiculite. The pH is usually between 7.0 and 7.5. Perlite can cause fluoride burn on some foliage plants, usually on the tips of the leaves. The burn progresses from the tip up into the leaf. Fluoride burns can be prevented by adding 1 1/2 times the recommended amount of lime when mixing the soil. A good formula for artificial mix follows.
  • 1 bushel shredded peat moss
  • 2 bushels perlite or vermiculite
  • 1/2 cup finely ground agricultural lime
  • 1/3 cup 20% superphosphate
  • 1/2 cup 8-8-8 or similar analysis mixed fertilizer
  • 1 level teaspoon chelated iron

Makes 2 bushels of media
Artificial mixtures are usually very low in trace or minor elements, therefore, it is important to use a fertilizer that contains these trace elements.
Soil Mixes for Specific Plants.
Soils must have the most efficient composition for the type of plant to be grown. According to generally accepted standards, we can divide indoor plant soils into four distinct groups, according to the type of plant to which they are most suited.
Foliage Plants:
This soil should be moderately rich, have a good base of clay loam, and hold moisture and fertility adequately. It must be a crumbly, well-textured soil. It is generally made up of one part of good garden loam, one part of clean sand or perlite, and half to one part of either peat moss, compost, leaf mold, or vermiculite. Mixing about 1 teaspoon of superphosphate with each quart of mixed potting soil is desirable and encourages good root growth after repotting. If the garden soil is alkaline, sphagnum peat moss will have enough acid reaction to neutralize the mixture. This soil is used for all foliage plants and some flowering plants that do not prefer a rich soil.
Flowering House Plants:
This soil is often referred to as humus soil because it contains about 50% humus-rich materials or similar ingredients. It is important that the soil does not become so rich that it is soggy after watering. Two parts of sphagnum, or one part sphagnum and one part vermiculite, are added to one part garden loam and one part clean sand. Also add 1 tea-spoon of superphosphate per quart of soil mixture. This soil is generally used for African violets, gloxinias, begonias, calla lilies, and other tropical flowering plants.
Cacti and Succulents: This soil does not need any humus material. It is composed of equal parts of sand, garden soil, and vermiculite or perlite. It is preferred for cacti and other fleshy leaved, desert-type succulents.
Orchids: Fir-tree bark or Osmundum fiber is generally used in glazed or plastic pots. The container should be large enough so that new growth is 1 to 2 inches from the rim of container. Broken clay pieces can make up the lower inch in the container.
Any soil containing garden loam should be pasteurized. This can be done easily at home. Spread the soil on a cookie tray and bake it at 180° F. for 30 minutes. Do not heat it longer than 30 minutes, and be aware that it will smell unpleasant while baking.

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