Modern potting mixes are developed to overcome some of the short falls of traditional soil based mixes:
1. Non availability of standardized top soil and manure: too often we now get subsoil and low grade, sticky manure.
2. Media containing a large proportion of soil are heavy.
3. They are aesthetically unacceptable: everything: plants, pots, floors and buildings etc are stained by the soil and drainage water.
4. Plant growth is relatively slow: this is due to poor aeration causing relatively sparse root growth. This may be actually desirable once the plant is full grown but at the production stage it is too wasteful.
At the same time, we must keep in mind the advantages of our traditional mixes and try and incorporate these into new media:
1. Years of experience with traditional media means that everyone in the production-marketing-customer chain is comfortable using it. This is one of the biggest stumbling blocks to using new and improved soil less media; since we have been using the soil less media from 20 years, we have long experience with it and confidence that it can be used successfully in
2. Low cost: soil and manure mixes are cheap. However, as my calculations show, they are not as cheap as we would think. New media using coir, thermocole etc are expensive but again, not as much as we may assume. If seen in the correct perspective, the benefits far outweigh the added costs.
3. Easy availability: though it would seem that both are easy to get, actually the situation is that it is getting increasingly difficult to get good top soil and well rotted, fibrous manure even if one is willing to pay. Alternate media components are not easy to source either- we have had to develop most of them in-house. We hope to offer superior grade materials at honest and competitive rates soon.
4. Traditional soil based media gives slow but compact, hard growth- this is an important benefit because of the way even ornamental house plants are handled (or mishandled) by our postproduction systems. However, by using the correct components in new soil free media and implementing correct fertilization procedure, it is possible to have good growth control in these new soilless media too.
The bottom line is that the only way to compete in today's tight market is to innovate, use new marketing tools and generally give a better product than the others can. The current situation is that the gardener who starts up on his own has rock bottom overheads and because he is hands-on and totally in touch with the plants, does a better job than the old time nurseryman who employs his growers. The only way to compete with such low cost producers is to learn and adopt new and more modern technology: clean, light weight soiless media is corner stone of modern pot plant culture and needs to be adopted by all forward thinking and ambitious nurserymen.
The greatest difficulty in implementing a soiless media program for your nursery is that it requires a systems change at various levels. Just as it is not possible to jump a 10 feet gap in 1 foot increments, it is difficult to introduce soiless media in a small way in your nursery. Understanding the concepts, developing a suitable media and then using it on a substantial scale is the only way to bridge this gap.
MEDIA CONCEPTS
1. WATER HOLDING CAPACITY (WHC): this is the amount of available water held by the media after watering and drainage. It depends on the choice of components used and can be adjusted to suit your needs. Whether your media needs higher or lower WHC really depends on: a) Size of the plant in relation to the pot- a large, established plant will absorb water rapidly while a recently planted, small plant in a large pot will tend to need much less water. b) Watering regimen: if you tend to water freely, a media with lower water holding capacity is better. The reverse is true if there is a chronic shortage of water. c) Season and environment: plants potted up during wet months will do better in a medium with lower water holding capacity because of less risk of over watering. Similarly, if the environment is generally hot and dry, you may want to have higher WHC.
2. AERATION: as long as plants are getting enough water (they usually do because we tend to over water and plants will droop when dry), the most critical component in the media is air. There is an inverse relationship between WHC and aeration- increasing one will decrease the other and vice versa. It is better to have a media with higher aeration and lower WHC because watering more is generally easier and economical but air cannot be added once the plants are potted and with time the aeration of the media will decrease.
A critical concept to understand for aeration is the difference between structure and texture; Structure refers to the way individual particles of a component (usually fine clay particles), are associated together (with humus) to form small clumps- because these clumps act is relatively large particles, they give an aerated medium. However, if the structure of these clumps breaks down (for e.g. by adding Sodium from Sodium nitrate containing fertilisers), the individual clay particles are so fine as to give a media with very poor aeration indeed. Texture, on the other hand, refers to the size of individual particles of any component. A course texture means larger particles and so larger empty spaces between particles for air to occupy. Thus fine sand will have less air and so poorer aeration compared to course sand. In addition to size of individual particles, the more uniform the particle sizes in the component, the better the aeration. If different particle sizes are mixed, the fine particles occupy the space between the larger particles, at the expense of air and so reduce media aeration markedly. Thus adding fine sand to a media will usually decrease aeration because the sand particles fill the gaps or voids between the larger media particles. (That is the principle of concrete: the large spaces between stone chips are occupied by sand and the space between the sand particles by cement, leaving no air spaces).
3. pH and SALINITY: These are very important considerations. Traditional media are used primarily because they naturally have acceptable pH and salinity levels. When moving to soil less media raises two pH problems: the buffering capacity of soil is removed so that pH can swing more easily and availability of micronutrients in soil less media is better at lower pH so one needs a lower pH for these media. The pH to aim for is between 5 & 6 and luckily most of the components available locally fall in this range. Once you move out of this pH range, all sorts of micronutrient problems start to occur. If your water supply is alkaline, some acidification of the irrigation water may be useful. pH meters are available but are difficult to maintain and calibrate. It is better to use a good quality pH indicating solution as accuracy is not really required, just the confidence that pH is within the desired range.
Salinity is often a problem with manures (chicken manure is particularly bad) and some coir supplies. Salinity is measured as the Electro Conductivity (EC) and is generally a measure of the salt (and roughly the fertilizer) content of the media.. It is always better to keep it low initially; once plants are growing it can be raised with liquid feeding. Good quality portable EC meters are now easily available and are a vital tool for all growers; make sure you buy one with the correct range and use it regularly to test salinity of media components, final mix and liquid fertilizers.
CLASSIFICATION of MEDIA COMPONENTS
There are two useful ways to classify media components; both systems are complementary and help in understanding media properties and aid in media selection & ratios to achive the desired objectives.
All media components can be classified based on their origin into Organic and Inorganic materials. They can also be classified based on their interaction with water as water holding or non water holding materials.
ORGANIC/ INORGANIC:
ORGANIC: material of plant origin and include coconut coir, sawdust, rice hulls, groundnut shells, manure etc. Points to keep in mind with organic materials are: · the C/N ratio - if too high, bacteria ( which are much more efficient than plants) will quickly absorb all nitrogen, leaving plants starved · salinity- especially when using manure and coir · rapid decomposition leading to shrinkage and deleterious changes in physical properties · toxicities: when using some sawdust's or bark · pests & weeds: from manure, groundnut shells etc · inconsistent quality: most items will vary from lot to lot
INORGANIC: material often though not always of mineral origin. Include sand, perlite, vermiculite, stone chips, thermocole granules, etc. Points to keep in mind here are: · They can suffer from all of the above problems except poor C/N ratio · Though they do not decompose, they can collapse like vermiculite to greatly reduced aeration. · Pests or weeds are generally not an issue but if stored poorly they can pick up weed seeds or pathogens. · Toxicity can often occur depending on the mineral origin of the product e.g. some stone chips may cause micronutrient toxicities or pH issues. Vermiculite available locally is for industrial use and often contaminated by oil residue etc.
ABSORBENT/ NON-ABSORBANT MATERIALS: Another way of looking at materials would be to classify them as water absorbing or non-absorbing. Strongly absorbing materials include coir, vermiculite and manure while totally non absorbing materials include stone chips and thermocole granules. Some materials will fall somewhere in the middle, e.g. groundnut shells. Once understood, intelligent use of this concept will allow minor modifications of a basic media to increase or decrease WHC and aeration to suit various crops and conditions.
