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Horticultural Perlite for Commercial Growers

Horticultural perlite is a grade of perlite developed for soil conditioning and other horticultural uses. It has been tested successfully at University Experimental Stations in various parts of the country. The use of horticultural perlite has gained wide acceptance with nurserymen, commercial growers, landscape architects and florists. Much of the knowledge accumulated through these tests, experiments and uses is presented in this booklet. Recommendations for the horticultural uses of perlite are based upon scientific data believed to be true and reliable but because conditions of use are beyond our immediate control, no warranty is expressed or implied concerning this material


Horticultural perlite is available nearly everywhere and it is packaged under various trade names. Most products fall into one of several gradations or classifications.


Commercial growers often use the terms "soil structure" and "soil texture" interchangeably in discussing soil characteristics, but this is neither accurate or correct. Soil texture refers to the size of the soil particles present in any mass of soil,while soil structure refers to the arrangement of these particles. Texture is more or less a permanent property of a basic soil a grower uses which he can usually change very little. Soil structure may and usually does change however. These changes are brought about by variations in the nature of the materials present in the soil which bind the particles together in several arrangements. These changes are accomplished by the manner in which the soil is cultivated, handled or used.

The maintenance of proper soil structure is equally or more important to the commercial grower than the maintenance of soil fertility. From a practical growing standpoint three types of soil structure are readily identified by the commercial grower, landscaper, or homeowner--single grain structure, crumb structure and "puddled" soil.


    Single grain structure is typified by sandy soil. It is loose, open, easy to cultivate and has many large individual pore spaces which allow a ready circulation of air and water through any volume of soil. Such soil structure is too loose and open, however, to absorb and hold sufficient moisture or nutrient material for maximum plant growth. There is only one satisfactory way of remedying this structural condition and that is to add organic matter of some sort, such as peat moss.

    When any organic matter undergoes satisfactory decomposition after it is incorporated in a soil, it will act as a binding material for the soil particles, and increase the nutrient holding and moisture capacity of the soil.


    Crumb structure is the type of soil structure that is most ideal for good plant growth, and is usually most likely to occur in a good loam soil. When crumb structure exists or is developed in a soil by the addition of soil conditioners it contains soil aggregates-large particles that function separately and medium to very small particles that may cluster together to form soil granules. When this occurs there are large pore spaces such as are found in a sandy soil, which provide excellent drainage and air movement in the soil, combined with many small pore spaces in which moisture and necessary plant nutrients are retained.


    Puddled soil, the third type of structural condition, is found in heavy clay soils where all the soil particles are extremely small and have a tendency to pack together so that poor air movement and poor drainage exists. Too much moisture and nutrient material is retained for maximum plant growth unless such soil is expertly handled.

While soil texture is a more on less permanent characteristic of any soil, texture can readily be changed to provide conditions for maximum plant growth by the addition of soil amendments or soil conditioners. The addition of these materials changes the arrangement of the particles in the basic soil, so that a suitable mixture for growing plants is developed that has the ideal crumb structure necessary to produce maximum plant growth.

The addition of soil amendments or soil conditioners is a common practice followed by most commercial growers in preparing soil for growing plants in pots, containers, greenhouse benches, nursery beds or nursery stock in the field.

Soil structure is often modified by adding organic matter, a good soil conditioner, gypsum, sulphur, and through the use of proper cultural procedures.

Horticultural perlite has proven to be an excellent material to use as a soil conditioner because it has certain characteristics Which provide the follow- ing results:

  • Soil structure is improved due to the near ideal air-water relation- ship that is developed in the growing media.
  • The air holding capacity of the soil is increased and adequate drainage is assured.
  • Overwatering and underwatenng losses are reduced due to the surface structure of the particle which retains 3 to 4 times its weight in water without penetrating the particle. Excess water will drain off.
  • Cracking and crusting of soil surface is reduced or prevented.
  • Soil compaction is prevented.
  • A more even distribution of the root system throughout the entire growing media is made possible.
  • Production costs are reduced in that the material is easy to handle, does not require sterilization and mixes may be accurately dupli-cated because of consistent perlite quality.
  • Shipping weights and transportation costs are reduced.
  • Uniform growing and propagating media are insured regardless of season or location.



  • Lightweight Soilless Growing Mix
    This growing medium is composed of 50% coarse sphagnum peat moss and 50% horticultural perlite by volume. The materials in this mixture are practically inert and it is important that adequate nutrients (fertilizer) be added to the mixture and that a fertilizer program be established during the growing period. To prepare a cubic yard of this lightweight potting mixture use the following ingredients:
    • cu. yd. Horticultural Perlite
    • cu. yd. Coarse Peat Moss
    • 3 lbs. 20% Superphosphate
    • 7 lbs. Dolomite
    • 4 oz. Fritted Potash
    • lb. Muriate of Potash
    • 3 lbs. Complete fertilizer with a 5-10-5 ratio
  • Growing Mix Containing Soil
    For growers who prefer to use some soil in their mixture this mix can be prepared in the following proportions for one cubic yard of potting mixture:
    • 1/3 cu. yd. Horticultural Perlite
    • 1/3 cu. yd. Coarse Peat Moss
    • 1/3 cu. yd. Soil


  • Perlite-Peat Mixtures
    Be sure the mixture is thoroughly wet when plants are potted. Do not pack the mixture when potting; water well after potting.
  • Soil Mixtures
    Be sure that the mixture is moist when potting is done. Do not pack mixture too firmly when potting; water plants well following potting. Do not water heavily again until new roots have begun to form.


  • Two-Week Feeding Schedule
    For growers who prefer not to feed with each watering, the following mixtures can be applied in liquid form every two weeks. You may use either a 15-30-15 soluble fertilizer applied I oz. to 2 gallons of water or apply oz. of potassium nitrate and oz. of calcium nitrate to 2 gallons of water. Iron chelates should be added to the fertilizer mixture at the rate of 1 oz. to 25 gallons of water about once a month.
  • Dry Feeding Program
    For growers who use dry fertilizer, the same program of feeding that has been used successfully for present soil mixture can be used on perlite-peat moss mixtures.
  • Feed at Every Watering Program
    For growers who prefer to apply fertilizer with every watering the following formula has been used very successfully.
    • 12 oz. Calcium Nitrate
    • 6 oz. Potassium Nitrate
    • oz. Iron Chelate
    • 100 gal. Water


A mixture of 1/3 perlite, peat moss and 1/3 soil is a good growing medium for these crops, or the stan4ardized medium can be used with nutrients added as recommended for container mixtures.

Prepare a mixture of one-part wet hor-ticultural perlite and one-part wet peat moss or other organic matter and spread in a layer two and one-half or three inches deep over the area and mix or cultivate well into the top six or eight inches of soil and add nutrients in the amounts recommended for con-tainer growing.


When used as a medium for propagation perlite will:

  • Provide excellent drainage while assuring adequate moisture hold-ing capacity.
  • Not compact or become soggy.
  • Prevent root losses when cuttings and seedlings are removed from the medium because of its capacity to cling to roots. This also reduces transplanting losses.
  • Last for indefinite periods because it resists breakdown with con-tinued and repeated use.

Mix one part wet perlite and one part of wet coarse peat moss by volume and fill propagating bench or flats. Stick the cuttings into the mix, firm lightly into place and water well.

Mix three parts of wet perlite and one part of moist peat moss by volume and fill propagating bench or flat and fol-low usual mist propagation proce-dures. Perlite used alone without the addition of peat moss is also used by some commercial propagators

Mix one-half wet perlite and one-half wet peat moss by volume. Fill seed flats or pots with mixture. Screen one-sixteenth inch of sphagnum or peat moss through a fine screen onto surface of flat or pot and sow seeds. Use screened material for covering seeds when required.

Spread one inch of wet perlite and one inch of wet peat on surface of seed bed and work well into top six inches of seed bed. Level surface of bed carefully and sow seeds in usual manner.


Before potting plants in pots or nursery containers place two inches of wet perlite in the bottom of the containers. This will insure adequate drainage and maximum root growth.


  • Packing, Storing, and Shipping
    Perlite is an excellent material for use as a lightweight packing material for rooted cuttings, dormant plants or bulbs.
  • For Plants and Cuttings
    Mix one-half wet perlite and one-half wet peat moss by volume, squeeze dry, and package plants or cuttings in the conventional manner.
  • For Bulbs
    Use dry perlite as packing medium for those requiring dry conditions, and for those requiring moist conditions use mixture recommended for plants and cuttings.
  • For Bulb Storage
    Perlite is an ideal material for use in maintaining a thermal and moisture barrier around stored bulbs, roots and tubers. Fill storage container to a depth of one inch with perlite. Place bulbs on this one inch layer and cover with perlite. In instances where some moisture is required, moisten the material very lightly with fine mist at very infrequent intervals.
  • Filler for Planters
    Perlite will serve to overcome a major problem in the proper maintenance of plants used in planters in residential and commercial applications.
    Plants used for this purpose should be well established and well watered before placing into planters or permanent tubs. Place two or more inches of perlite in the bottom of the planter or tub. Use enough additional perlite under plants to raise them to within two inches of the top of the planter. Using a mixture of one-half wet perlite and one-half wet peat by volume, fill all the remaining area around and above the plants and pack the material lightly.
    In maintaining the plants after planting keep the material surrounding the plants uniformly moist but not wet. Planters using perlite/peat moss weigh about 35 lbs/cu. ft. (560 kg/rn3) as opposed to planters using a conven-tional wet sandy loam that weighs about 120-140 lbs/cu. ft. (1920-2240 kg/rn3).

Information given herein is from sources considered reliable, but no guarantee of accuracy can be made or liability assumed.  Your supplier may be able to provide you with more precise data.  Certain compositions or processes involving perlite may be the subject of patents.
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