Growing media for horticultural crops
Authors: Poonam Kumari, Sapna Panwar and Namita
Division of Floriculture and Landscaping
ICAR- IARI New Delhi- 110012
Correspondence address:

The production of horticultural crops involves a number of cultural inputs. Among these, the most important is the type of growing medium used. Media (Substrate) is the substance, provides anchorage to the plants by holding the root system. It also provides the essential plant nutrients required for the metabolism, growth and development of the plants. Either single medium or the combination of two or more media is used as substrate. Due to the relatively shallow depth and limited volume of a container, growing media must be amended to provide the appropriate physical and chemical properties necessary for plant growth.

Criteria for selecting media

  1. Dense and firm enough to hold the root system intact
  2. Enough nutrients in reserve
  3. Should have neutral pH (5.6 to 6.5)
  4. Should not shrink or expand easily
  5. Good drainage, porosity, aeration, etc.
  6. Easily available
  7. Economic
  8. Should be sterilized easily
  9. Free from pathogens, pests and weed seeds etc.
Description of some of the most commonly used growing media for the production of horticultural crops

Soil: Soil is the basic material/ ingredient of the media. It forms the major portion in the combination of different media. It is cheaply available, economic and easy to handle. Forest soil which contains good amount of humus and organic matter is preferred. It is easy to carry out sterilization and disinfestations.

Sand: Sand is a naturally occurring granular material composed of finely divided rock and mineral particles, ranges in particle size from 0.05mm to 2.0mm in diameter. The most common constituent of sand is silica (silicon dioxide, SiO2), usually in the form of quartz. Because of its chemical inertness and considerable hardness, it is most commonly used as a component in media. Medium and coarse sand particles are those which provide optimum adjustments in media texture. Although sand is least expensive of all inorganic amendments but it is also heavier in nature. This may result in prohibitive transportation costs. Sand is a valuable amendment for both potting and propagation media.

Sphagnum moss: Sphagnum moss is the dehydrated remains of acid-bog plants from the genus Sphagnum (Sphagnum papillosum). It is light in weight and has the ability to absorb water 10 to 20 times of its weight. This is attributed to the large groups of water holding cells, characteristic of the genus. Sphagnum moss contains specific fungistatic substances which accounts for its ability to inhibit damping-off of seedlings. Sphagnum moss is the most desirable form of organic matter for the preparation of growing media.

Compost: Compost is the well decomposed organic matter obtained by aerobic/anaerobic decomposition. The compost soil is a soil conditioner, a fertilizer to add vital humus or humic acid, and acts as a natural pesticide for soil. Cardboard paper, coffee grounds, coir, garden waste, night soil, leaves, seafood, manure, mushrooms, spent mushroom substrate, tree bark, eggshells, fruit and vegetable wastes, seaweed etc. can be effectively used for composting. Compost is generally recommended as an additive to soil, or other matrices such as coir and peat, as a tilth improver, supplying humus and nutrients. It provides a rich growing medium, or a porous, absorbent material that holds moisture and soluble minerals. Provides the support and nutrients in which plants can flourish well. It is rarely used alone, but being primarily mixed with soil, sand, grit, bark chips, vermiculite, perlite, or clay granules to get better results.

Cocopeat: Cocopeat is a versatile natural fiber extracted from mesocarp tissue, or husk of the coconut fruit. The husk contains 20-30% fiber of varying length. After grinding the husk, the fibers are removed and used for preparation of coco- pith which is commonly used as medium. Cocopeat is known as coir pith or coir dust. Cocopeat holds 8-9 times its weight in water. Cocopeat has the ability to store and release nutrient to plants for extended periods of time. Cocopeat can be reused for up to 4 years. Cocopeat disintegrate very slowly, only begins to break down when it is 10 years old. The properties of cocopeat make it resistant to bacterial and fungal growth.

Charcoal: Charcoal is the blackish residue consisting of impure carbon obtained by removing water and other volatile constituents from animal and vegetation substances. It is usually produced by slow heating of wood, sugar, bone char, or other substances in the absence of oxygen. The resulting soft, brittle, lightweight, black, porous material resembles coal and is 85% to 98% carbon with the remainder consisting of volatile chemicals and ash. It is commonly used as potting medium for growing orchids.

Shredded bark/wood bark: Fir Bark is the most popular orchid potting medium. It is fairly light and easy to handle. It has a rough surface and does not compact, allowing air and water to be obtained by the plant's roots. Fir bark is available in three grades:

  • Fine -- Used for orchid seedlings or mature plants with fine roots.
  • Medium -- Used for epiphytic orchids.
  • Coarse -- Used for Vandas and large Phalaenopsis orchids.

    Redwood Bark is similar to fir bark, but is more resistant to decay. Since redwood bark is imported, it costs more than tree fern fiber so it tends to be used more as an addition to potting mixes. Crushed Cork is another mixture additive. It should not be used alone as it tends to break down quickly.

    Vemicompost: Vermicompost is the organic manure also known as worm castings, worm humus or worm manure, is the end-product of the breakdown of organic matter by the earthworm. The process of producing vermi compost is called vermi composting. Vermicompost is rich in many nutrients than compost produced by other composting methods. It can also outperform a commercial plant medium. It improves the physical structure of soil and enriches soil with micro-organisms (adding enzymes such as phosphatase and cellulose). Microbial activity in worm castings is 10 to 20 times higher than in the soil and organic matter that the worm ingests. It enhances water holding capacity, germination, plant growth, crop yield, and root growth.

    Leaf mould: Leaf mould is a form of compost produced by the fungal breakdown of shrub and tree leaves. It is generally dry, acidic, or low in nitrogen for bacterial decomposition. Leaf mould is a type of soil conditioner. The addition of leaf mould increases water retention in soils by over 50%. It also improves soil structure and provides a fantastic habitat for soil life, including earthworms and beneficial bacteria.

    Perlite: Perlite is a unique volcanic mineral which expands to about 13 times its original volume when it is heated to a temperature of approximately 1600 F (871C). During the heating process, the mineral particles pop like popcorn and form a granular, snow-white material that is so light in weight it weighs only about 5 to 8 pounds per cubic foot (80-128 kg/m3). Each particle of perlite is comprised of tiny closed air cells or bubbles. The surface of each particle is covered with tiny cavities which provide an extremely large surface area. These surface cavities trap moisture and make it available to plant roots. In addition, air passages are formed in the growing media thereby providing excellent aeration. Perlite acts as an insulator to reduce extreme soil temperature fluctuations. It is sterile and free of weeds and disease. It is clean, odorless, lightweight, and safe to handle.

    Vermiculite: Vermiculite is a micacious mineral produced by heating to approximately 745oC. The expanded, plate-like particles which are formed have a very high water holding capacity and aid in aeration and drainage. Vermiculite has excellent exchange and buffering capacities as well as the ability to supply potassium and magnesium. Although vermiculite is less durable than sand and perlite, its chemical and physical properties are very desirable for container media. It is used as soil additive for plants, together with perlite for potted plants. It is suitable growing medium for hydroponics.

    Pumice: Pumice is a textural term for a volcanic rock that is solidified frothy lava. Typically created when super-heated, highly pressurized rock is violently ejected from a volcano. It can be formed when lava and water are mixed. This unusual formation is due to the simultaneous actions of rapid cooling and rapid depressurization.

    Rock-wool: Rock-wool is a horticultural growing medium made from natural ingredients - basalt rock and chalk. Rock-wool for hydroponics is formed when heated at 1600oC, into lava. The rock-wool lava is next blown through a large spinning chamber. It is pulled into fibers, which resemble cotton candy or the same lava fibers that fly around in a live volcano. After the rock-wool fibers are spun, they are compressed into mats that can be cut into slabs or cubes for hydro growing
  • Hydrophilic rockwool or hydrophobic granulate rockwool: it is often incorporated into peat moss soil in order to improve the tilth of the soil. Hydrophilic and Hydrophobic granulate rockwool are water absorbent or water repellent respectively.
    • Rockwool rigid slabs, blocks or cubes: fibers are held together with a binding agent, which makes the blocks and cubes stiff and brittle. It is used in displays of cut flowers.

      Peat: Peat is an accumulation of partially decayed vegetation matter. It is formed in wetlands or peatlands, variously called bogs, moors, muskegs,pocosins, mires, and peat swamp forests. Peat forms when plant material, usually in marshy areas, is inhibited from decaying fully by acidic and anaerobic conditions. Peat is an important media. The most important property of peat is retaining moisture in soil when it's dry and yet preventing the excess of water from killing roots when it's wet. Peat can also store nutrients although it is not fertile itself.

      Different types of Peat:
  • Moss peat
  • Reed - sedge peat
  • Peat humus

    Commonly used soilless mixtures for production of horticultural crops
Components Volume Ratio
Peat, Perlite 2:1
Peat, Perlite, Vermiculite 2:1:1
Peat, Sand 2:1
Peat, Sand 3:1
Peat, Perlite, Vermiculite 3:1:1
Peat, Bark, Sand 2:1:1
Peat, Bark, Perlite 2:1:1
Peat, Bark, Sand 3:1:1
Growing bag technique using soiless media

Growing Bag is a long tubular bag that has growing media (like coco peat) filled in it. Small holes are made on the top at a distance of 30 to 40 cm, depending upon requirement. Fertigation is given through these holes using inline drip irrigation system. 30- 45 mm long slits are made at the base of the growing bag in order to drain out excess water. This system is very efficient as it minimizes the chances of getting any disease through soil and enhances the productivity of the area and other inputs. This system can also be used on sloppy or undulating surfaces. Coco-peat (Coir) growing bags are widely used in hydroponic industry. It is very good alternative to traditional peat moss and rock wool. The coco-peat/coir grow bags can be used up to 3 years. It is commercially utilized under protected cultivation in capsicum, tomato, lettuce, strawberry etc.

About Author / Additional Info:
I am currently pursuing Ph.D in Floriculture and Landscaping from Indian Agricultural Research Institute, New Delhi.