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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
GRADING
Horticultural perlite is available nearly
everywhere and it is packaged under various trade names. Most products fall into one of
several gradations or classifications.
PERLITE AS A SOIL CONDITIONER
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
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
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
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.
POTTING PLANTS AND CONTAINER
GROWN NURSERY STOCK
TYPICAL MIXES
- 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:
- ½ cu. yd. Horticultural Perlite
- ½ cu. yd. Coarse Peat Moss
- 3 lbs. 20% Superphosphate
- 7 lbs. Dolomite
- 4 oz. Fritted Potash
- ½ 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
POTTING PROCEDURES
- 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.
NUTRIENT FEEDING OPERATIONS
- 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 ½ oz. of potassium nitrate and ½ 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
- ½ oz. Iron Chelate
- 100 gal. Water
GREENHOUSE BENCHES
A mixture of 1/3 perlite, ½ 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.
PERLITE AS A PROPAGATING MEDIUM
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.
CONVENTIONAL VEGETATIVE PROPAGATION
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.
MIST PROPAGATION
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
SEED FLATS
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.
SEED BEDS
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.
USE OF PERLITE FOR DRAINAGE IN
CONTAINERS
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.
OTHER HORTICULTURAL USES OF
PERLITE
- 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).
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