Chemical Fertiliser vs Vermicast
You may find chemical fertilizers may be a cheaper option to fertilize your plants. In most cases they will provide immediate nutrition to your plants as your plants are basically force fed.
You will see immediate responses from the plants which will absorb only what they require and then the rest is left in the soil. Many of the chemical fertilizers have now been proven to be toxic to the life in the soil and so great damage is done to the soil life and hence the soil aggregation (lack of crumbly appearance , no space for Oxygen and water penetration) as well. Being water soluble the fertilizers are also prone to being easily washed out of the soil. In areas where this is happening over a large scale there is the possibility of great harm to the natural eco-system in the surrounding areas ie rivers, dams, (algal growths), oceans(Great Barrier Reef for example). In the long term this is not the most sustainable option.
Plants have been on this planet for millions of years. We have been led by the big multi nationals to believe the only way to grow plants successfully is with the addition of chemical fertilisers, fungicides etc. But how have plants been fertilised by Nature in the past millions of years? Nature has provided a natural way to fertilize plants through micro-organisms breaking down organic matter into plant usable forms. Worm castings is largely about providing millions of micro-organisms and so build up that ecology naturally which in turn will support the surrounding soil. Our soils typically now contain far less life than prior to the introduction of chemicals. Worm casts contain an incredibly diverse set of micro-organisms which will grow and thrive when applied into a favourable environment (your garden?) Many of the thousands of different species of bacteria, archea and fungi have not been identified yet, nor their role understood. In fact this may always be the case as many of them will not culture in a laboratory and so cannot be studied in isolation.
We have all heard of humus and accept that it is good for our soil. Humus contains large carbon chains with many elements ie Nitrogen, Phosphorus etc which are bonded to the chains. It is the microorganisms roles to break these bonds and make the nutrients available to the plant. Each element may require a unique bacterium or fungi to release a particular chemical bond or to form a new bond. There is evidence now of plants responding to a need for a mineral by releasing exudates that will grow the type of microbe needed to release that particular nutrient. So it is a natural slow release of nutrients at the rate that the plant requires. Also the environment created around the plant root will become aggregated so that water and air can flow easily through the channels created.
You may be tempted to add large volumes of vermicastings (if you can afford the expense). It has been proven many times over that worm castings should not used on its own. I can share with you my experiences as to how I utilise castings in my garden. In an experiment I did with potted plants, different mixes of aged horse manure and worm castings were applied. The pots with 100% horse manure grew ok, the pot with 100% worm cast didn’t grow too well, but the pot with a mix of aged manure and worm castings had significantly better and healthier plants. The optimal ratio of the mix seems to be 1:4 worm castings to compost. This type of experiment has been repeated many times over in labs and fields with various mediums mixed with castings. The results are always the same. This is why I tell customers no more than 20% by volume of castings as a general rule seems to give consistently good results.
If we think about it, all earth worms produce castings to help supplement the surrounding soil, never in the natural environs was 100% of it used to grow a plant, it is slowly added over time. This is Nature at work.