There are two main types of fertilisers: inorganic (man-made) and organic (derived from plant or animal).
Inorganic fertilisers: These are synthetic, artificial forms of plant nutrients or naturally occurring mined minerals. Inorganic fertilisers are usually more concentrated and faster acting than organic fertilisers. Examples of inorganic fertilisers include: Growmore, Miracle-Gro, Phostrogen, Sulphate of Ammonia, Sulphate of Potash, and Superphosphate and Tomorite
Organic fertilisers: These are derived from plant or animal sources and contain plant nutrients in organic form. Organic products tend to be slower acting, as large organic molecules have to be broken down by soil organisms before the nutrients within them are released for plant use. Examples of organic fertilisers include: seaweed, hoof & horn, dried blood, fish blood & bone, bone meal, poultry manure pellets and liquid comfrey or nettle feeds.
Inorganic and organic fertiliser can be found as the following types of products:
Compound fertilisers: These contain a mixture of different nutrients, and may be balanced (containing similar proportions of all the major plant nutrients) or may supply more of some nutrients than others, as per the requirements of different crops. They may be organic or inorganic, or contain both.
Straight fertilisers: These contain only one or mainly one nutrient. They are usually used to provide different nutrients at different times of the year, or to correct particular nutrient deficiencies. They are usually inorganic.
Controlled release fertilisers: These are almost always granules of inorganic fertilisers coated with a porous material such as sulphur or synthetic resin. Water enters the granule and the fertilisers leach out into the surrounding soil. The warmer the soil, the faster the leaching; this corresponds to plant growth which is faster in warm weather. By varying the thickness of the coating granules can be designed to feed plants for different periods of time.
Slow release fertilisers: These degrade slowly, usually under the influence of soil micro-organisms to release their nutrients and again are dependant on soil temperature. These are usually organic and include hoof & horn and bone meal.