Well it seems that there is a bit of discussion on what fertilizers are best organic vs inorganic, so I thought I would write a bit about what I know concerning plant nutrient uptake and community interactions.
As Charlie stated previously, fertilizers are nutrients for plants, plain and simple. Plants need Nitrogen, Phosphorous and Potassium (and a few micronutrients Mn, Zn, Mo, Fe, etc..) for good growth and flowering. When plants are grown in the ground, in the wild without human interaction, these nutrients are supplied via decomposition byproducts of dead material. There is a complex composition of microorganisms which make up the rhizosphere (root area) of plants. As long as there is a continuous application of these nutrients from any source, usually via decomposition, there will be good growth and flowering. As Darren has shown with his plants last year, a generous supply of organic matter to the soil gives all the nutrients they need and leads to great growth and flowering. (Yes all those amazing pictures he showed were without the use of any application of fertilizer, only great soil chemistry!) With increased concentration of certain nutrients, potassium in particular, we can augment the flower pigment production and cell wall composition of our plants. If these vital nutrients for growth are not present in the soil, then they will need to be added via fertilization. Plants in the ground can actively grow additional roots to seek out missing nutrients.
This differs from pots, where the environment is confined and nutrients limited.
So what is happening in the potted environment? As plants grow, roots begin to replace soil as the soil and nutrients in potting soil break down. After this occurs, there is no longer sufficient nutrients to support growth and it must be supplied externally, via fertilization.
So what is the difference between organic and inorganic fertilizers? To the plant, as long as it gets the N-P-K ratio it requires to grow, the source doesnt matter.
Inorganic fertilizers are usually bound to different salt ions, which is where the problem of salt burn stems from. With inorganic salt-rich chemicals, (usually Chloride salts) if you over fertilize your plants, they become hypotonic and essentially dry out. This is why when you observe salt burn in plants the symptoms include browning of the leaves. The manufacturing of these fertilizers is also very energy intensive and requires the use of raw materials. Since the chemical nature of these compounds are simple salts, they are very fast acting and very water soluble. Inorganic fertilizers also do not stick around in the soil, requiring more consistent application.
Organic fertilizers are produced either by waste excrement by animals (cow and chicken manure) or decomposition of plant material. As Charlie has stated, these fertilizers seldom have the right N-P-K ratio required for hibiscus separately, as usually animal based fertilizers are high in nitrogen and phosphorous and low in potassium. However, seaweed based fertilizers do contain high levels of potassium. Therefore you could easily apply an animal based fertilizer, in conjunction with seaweed, to produce a ratio that is ideal for hibiscus. These seaweed fertilizers also contain the micro-nutrients required for growth as well. Organic fertilizers also tend to last longer in the soil when compared to inorganic salt-based fertilizers. This is likely due to the fact they usually exist as bigger molecules and are often a more "bio-available" form of the nutrient. Although there are a few cases of overuse of concentrated chicken manure causing ill effects, I have not been able to find any evidence to support that this is true for other sources of organic fertilizers. Bottom line, natural sources of these nutrients do not exist in high enough concentrations to cause problems and do not contain the salts associated with synthetic fertilizers.
With that being said, I have used both HVH special blend and the organic fertilizer previously offered by HVH with equal results. Organic fertilizers allow a bit more wiggle room as far as "hickups" in dosing are concerned, but both provide the nutrients required for good growth and blooming.
Over-fertilization can cause environmental problems associated with nutrient leaching, but a well structured and accurate dose of nutrients will keep both your plants and environment happy
