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Lecture 4 – CS 5120
Propagation MediaCharacteristics, components and
Preparation
1
Introduction
• The health and quality of horticultural crops rest largely with the growing medium
• The growing medium is the material in which plants are grown
• In field production and homegardens,
soil is the growing medium
• Soil is used for plant propagation and
in horticulture nursery from ages
• Different growth media are prepared and used successfully in modern nurseries
Introduction cont’d..
Growing Medium
• A growing medium can be defined as …..
“A substance through which roots grow
and
extract water and nutrients”
Growing Medium Cont’d….
• Selecting the proper growing medium is one of the most important considerations in nursery plant production
Growing media
• Should provide adequate drainage and aeration
• Should meet the needs of plant roots for air, water, nutrients and support
• These needs will vary….
depending on the plant type and its stage of growth
Growing Media cont’d..
• Plants can be grown in different media, if proper management is provided
• An ideal medium should be
– sterile,
– Light weight,
– porous,
and consistent in quality
• Vary depending on the plant and its stage of growth
6
Functions of the Growing medium?
Growing medium serves 4 basic functions for plants
1. Growing medium holds water for plant use
2. Growing medium provides nutrients for plant
growth and development
3. Growing medium permits the exchange of
gasses to and from the plant roots
4. Growing medium provides support for the
plant by giving roots firm anchorage
Good Medium • Must be firm to hold the plant and volume of media
should be constant under wet or dry condition• Should be porous, drain out excess water and provide
aeration and at the same time retain sufficient moisture in it
• Should be free from weed seeds, nematodes and harmful pathogens
• Must have a neutral pH • Must be capable of being sterilized without deleterious
effect in porosity, structure and texture
Properties of a Good Growth Medium
Criteria for Selecting Ingredients for Media
1. Hygiene status
Must be free of all pests, diseases and weeds;
• Some materials are sterile –
eg. perlite, vermiculite
• Some may need treatment
eg. compost9
Criteria for Selecting Ingredients for Media cont’d…
2. Available Air
- The “air-filled porosity” (AFP)
the percentage of the container which contains air
• Need to be in the range of 25-40%
• It is the non-solid portion of the volume
10
• A higher percentage of pores or porosity in a media results in better water drainage and aeration
• The higher the AFP, … more water needed
• Good garden soils have about 50 % pore space
• Organic media used in potting media have between 75% and 85 % pore spaces
• Should have sufficient pore spaces to allow an exchange of carbon dioxide and oxygen
2. Available Air cont’d…
• Adequate media aeration is vital to root
growth
• Water-holding ability is also important,
though secondary to aeration
• Since roots require oxygen to function
properly, a poorly aerated media will
restrict root growth and lead to root
death
• Available Water- Available water is water that can be
absorbed by the plant roots- Available water is found in the pore spaces of the medium
The amount of water available in the mix will determine the frequency of watering needed
14
Criteria for Selecting Ingredients for Media cont’d…
• The amount of water held in a particular
medium is dependent upon
- the particle size distribution and
- the container height
• Root distribution in container media can
be influenced by the particle size
distribution.
• A medium with high water-holding
capacity and low aeration may result in a
concentration of roots in the top portion
of the container
4. Correct pH
The pH should be in the range 5.0 – 7.0
1. Adjust upwards with dolomite
2. Adjust down with Sulphur
16
Criteria for Selecting Ingredients for Media cont’d…
pH and Nutrient Availability
• Low pH causes toxicity for certain
micronutrients (Zn, Fe, and Mn)
and
deficiency of Mg
• High pH reduces availability of
certain nutrients such as P, Zn,
Mn, Fe, and B
5. Soluble salt levels
Young plants are very sensitive to high salt levels;
Salinity arises from:
• potting mix ingredients
• the fertilizer program
• the irrigation water19
Criteria for Selecting Ingredients for Media cont’d…
5. Consistency of Quality
Each batch of a given material should be consistent in quality
20
Criteria for Selecting Ingredients for Media cont’d…
6. Ease of Mixing
All materials should be capable of being mixed easily
21
Criteria for Selecting Ingredients for Media cont’d…
7. The presence of toxic substances
Wood based materials may contain Phenolic compounds which can be toxic to small plants
The materials must be properly composted to allow them to leach out
22
Criteria for Selecting Ingredients for Media cont’d…
8. The problem of nitrogen depletion in wood based products
- N may be temporarily depleted as a result of bacterial decomposition,
which
requires the uptake of nitrogen by the bacteria
23
Criteria for Selecting Ingredients for Media cont’d…
Selecting Ingredients for Media
9. Cost
Imported materials such as peat and vermiculite are expensive;
Growers are looking for cheaper, locally available materials
eg. Cattle manure, compost, decayed leaves etc.
24
Factors that determine the cost of a
growing medium include …….
• transportation,
• labor,
• equipment,
• materials
and
• handling
25
10. Weight of the finished mix
Heavy materials difficult to use;
Extraction of
- seedlings or
- rooted cuttings from trays is
difficult with a heavy mix26
Criteria for Selecting Ingredients for Media cont’d…
11. Simplicity of the mix formula
• Complex mixes are difficult to prepare
• The complexity often leads to mistakes
27
Criteria for Selecting Ingredients for Media cont’d…
Examples
Orchids
different growing material needs from other plants like trees or
vegetables.
instead of organic soils and composts, Orchids need an appropriate
mix of water retaining and aerating materials.
The ratio depends on the type of orchid.
Coconut Husks among the first fibers to be used for orchids. -
- Inexpensive, light weight, holds water moderately
well,
but decays more quickly
Anthuriums
Whether in pot or bed,
• grows well in a medium of high organic, well
aerated with good water retention ability, with
good drainage
• should be light,
• Ingredients –
wood shavings,
saw dust,
leaf prunings,
wood charcoal and
farmyard manure
• Availability of material
• Cost/price (production and transportation)
• Steady production- quality and quantity
• Environmentally-friendly
• Suitability to provide desirable physical
and chemical properties for production of
nursery and greenhouse crops
Selection of Alternative materials
32
1. Porous and well drained, 2. Retentive of sufficient moisture to meet
the water requirements of plants 3. Relatively low in soluble salts, but with an
adequate exchange capacity to retain and supply the elements necessary for plant growth
An effective program should produce a growing media that is
33
4. Free from harmful soil pests; pathogenic organisms, soil insects, nematodes and weed seeds
5.Standardized and uniform with each batch to permit the use of standardized fertilization and irrigation programs for each successive crop
6.Biologically and chemically stable following pasteurization
Testing the Media before a crop is planted….
Test the media for 1. pH, 2. soluble salts, and 3. Available nutrients
Testing the Media
34
Imported potting soil should test to determine the need for
– amendments/nutrients
Monitor soils for pest organisms
container soil mix shall be of proper composition
and
appropriate media for specific plant growing needs
35
Sterilization of Media
• Chemical fumigants or steam heat are typically used to sterilize media.
• Fertilizers or other chemical amendments are sometimes added to growing media during the mixing process.
• Dolomitic limestone is used to supply calcium and magnesium and
• To raise the low pH
36
Characteristics of ideal substrate for germination and rooting of cuttings
• Firm and dense to hold cuttings or seed
in place
– volume must be fairly constant when wet or
dry
– excessive shrinkage after drying is
undesirable
• Highly decomposed and stable to prevent n
immobilization and excessive shrinkage during
production
20 : 1 Ratio of C : N Preferred
• Easy to wet and retain enough moisture to
reduce frequent watering
Characteristics of Ideal Substrate for Germination and Rooting of Cuttings
• Sufficiently porous so excess water drains away,
permitting adequate penetration of oxygen to the
roots
• Free of pests—weed seeds, nematodes, other
pathogens
• Low salinity
Characteristics cont’d..
• Capability to be steam pasteurized or
chemically treated without harmful effects
• High CEC for nutrient retention
• Consistent quality from batch to batch
• Readily available and economical
Characteristics cont’d..
• There is no single, ideal mix
• Appropriate mix depends on
the plant species/propagule type
(seed vs. Cuttings),
season,
propagation system (fog vs. Intermittent mist,)
cost,
availability of components
• Organic Components
– Peat
– Softwood and Hardwood Barks
– Sphagnum Moss
– Sawdust, Leaf Mulch, Rice Hulls
oxidize readily,
compact easily and
have high C:N ratio
Propagation Media cont’d..
Ingredients
• Coarse Mineral Components
– Sand (Avoid Fine Particle Sand)
– Perlite
– Vermiculite
– Clay Granules
– Rockwool
• Synthetic Plastic Aggregates
– Chemically Neutral
– Do Not Absorb Water
– Do Not Decay
– Environmental Problems with Production and
Disposal of these Materials
• Rockwool
– Rock Materials that Are Melted then Spun into Fibers
and Pressed into Blocks with a Binder Added
– Available Shredded, as Pellets, Slabs, Blocks, Cubes, or
in Mix with Peat Moss
• Soil
– If used as a propagation medium,
– must be amended with other components to
improve aeration and to prevent compaction that
occurs when mineral soils are placed in a container,
and must be pasteurized to kill soil borne pests
• Coconut Fiber—Coir dust
– Derived from Coconut Husks
– Economical Peat Substitute
Coir Dust
• It is high in P, K, Na, and Cl
• While coir dust serve as a source of these mineral elements, Na and Cl levels
may cause problems when used with
irrigation water that has
higher levels of Na and Cl
• Provides a good buffering capacity
Sand
Sand is often used in media mixes to add
bulk density and improve drainage
Choose particle sizes of 0.05 to 1.0 mm
with at least 90 % of the particles towards
the finer range
No nutrients or buffering capacity
50
51
• Bi-product of the rice milling industry • extremely light in weight, • very effective at improving drainage • N depletion is not a serious problem in
media amended with rice hulls
Rice Hulls
Animal Manure
• Heavy
• expensive to transport long distances
Potential dangers of manure include:
• Soluble salt damage from high nutrient content,
• Ammonia damage to roots and foliage,
and
• Weed seeds, insects, pathogens and nematodes contained in non-pasteurized or non-fumigated manures
52
• Compost
– Compost is produced from biological
decomposition of bulk organic wastes under
controlled
– Potting mix should not contain no more than
30% by volume compost
• Compost prepared primarily from leaves may
have high soluble salt content which inhibits
plant growth
Can lower salinity by leaching compost before use
In compost piles
• Usually find high numbers of bacteria, fungi,
nematodes, millipedes, soil mites, beetles,
springtails, earthworms, earwigs, slugs etc.
If use compost,
• make sure to use high-quality compost at the right stage of maturity
• Unfinished compost may release volatile organic acids that can negatively affect seedling growth and development
• One classic method of evaluating compost readiness is by smell
• Finished compost has a sweet smell
Sphagnum peat moss
• Sphagnum peat moss comes from mosses
(Sphagnum hypnum, etc)
• Contains long fibers which resist
decomposition
• Sphagnum moss is acidic,
with pH ranging from 4.0 to 5.0, and
• Usually has a very low fertility level
Perlite
• Perlite is a granite-like volcanic
material,
• Crushed and heat treated to
pop into white, hardened
particles
• Its role potting mixture is
aeration
• Does not hold water and
nutrients
• pH is between 7.0 - 7.5
Physical and chemical properties of the substrate
A substrate should:• be light in weight to ease transport to the
planting site• hold cuttings or seedlings firmly in place• retain enough moisture to avoid need for
frequent watering• be porous enough for excess water to drain
easily• allow sufficient aeration of the roots
Physical and chemical properties cont’d…
• free from seeds, nematodes and diseases• able to be sterilized without changing
its properties• have enough nutrients for a healthy initial
development of plants• not have a high salinity level• a suitable pH• be stable and not swell or shrink
excessively or crust over in the sun
Summary
It is important to formulate media mixes that:
- Provide optimum physical and chemical
properties
– Promote plant growth
– Retain water and reduce loading of nutrients
in leachates and runoff water
– Reduce fertilization and irrigation amounts
through efficient use of water and nutrients
– Environmentally and economically sustainable