lecture 4 cs 5120 propagation media · preparation 1. introduction •the health and quality of ......

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

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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

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• 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

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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

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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

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Criteria for Selecting Ingredients for Media cont’d…

6. Ease of Mixing

All materials should be capable of being mixed easily

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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

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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

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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.

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Factors that determine the cost of a

growing medium include …….

• transportation,

• labor,

• equipment,

• materials

and

• handling

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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

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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

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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

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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

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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

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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

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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

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• 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

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• 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