Notes on Fertilisers
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Why do we need to fertilise our plants?
For a start, unless you are growing pldants in their natural habitat and returning all waste matter to the soil, the soil will need to be fertilised to replace lost nutrients.
As well, those plants that originate in soils with higher nutrient content will need to be fertilised to grow happily.
Another reason for fertilising is that, in time established plants use up all the goodness in the surrounding soil.
 
And some plants, such as fruit trees, vegetables and roses, have been bred to be super productive and need extra. Lawns are other good examples. Every time the lawn is mowed and the clippings removed, the plants have to begin growing their leaves again. 
It is important to be aware that fertilisers are not ' food ' for plants - plants manufacture their own sugars from the sun - but are necessary to enable plants to function effectively. However, generally, the term ' plant food ' is commonly used when referring to fertilisers.
Types of Fertilisers:
Animal Manures - These are excellent for improving soil structure when used in relatively large quantities, but their nutrient value is relatively low and very variable, depending on the type of manure and the animal's diet.
 
Pelletised Poultry and Sheep Manures - Manure has been compressed into pellets and dried so that, as the pellets break down, the nutrients release gently over a long period.
Blood and Bone - This is the original  'slow  release '  fertiliser. It is made from waste products of abattoirs and provides a very gentle, long-term feeding. It does not contain potassium.
 
Green Manure Crops - A leguminous plant such as peas, is grown (because it can trap atmospheric nitrogen ) and dug into the soil after flowering. The use of green manure crops is limited by the space available.
 
Powdered and Granular Fertilisers - Come in different formulations to suit different types of plants. These usually contain a high proportion of soluble nitrogen so can be very damaging to roots unless there is plenty of water available to assist the nitrogen to dissolve. Always supply to a moist soil and water well after application. Specific formulations are recommended for particular plants ( e.g. potatoes, onions, lawns ). 
 
Water Soluble and Liquid Fertilisers - These types of complete fertilisers are designed to dissolve rapidly in water and applied directly to the plant by watering can or a hose-spray attachment.
Controlled Release Fertilisers - These are a relatively new developments in fertilisers and they have revolutionised fertilise application. They consist of a soluble fertiliser particle surrounded by a protective coating. Water penetrates the coating and dissolves the fertiliser, which then begins to seep through the coating. The rate of nutrient release is controlled by temperature, which means that more nutrients are released when the plants are actively growing.
Calcified Seaweed - Is a calcareous algae resembling coral, known to marine biologists as Lithothamnium Calcareum. It is dredged from the sea bed mainly off the Brittany coast, dried at low temperatures and crushed to a fine powder, which is readily assimilated by the soil. It contains about 46% calcium oxide, 5% magnesium oxide, sulphur, copper, iodine, cobalt and some twenty trace elements. It is an ideal soil conditioner and clay breaker, and can be used on lawns, beds and borders as an alternative to lime to correct soil acidity. It is highly favoured by chrysanthemum, sweet pea, dahlia, leek and onion growers.
Superphosphate - Is a rich phosphorus fertiliser for stimulating root growth in trees, shrubs and lawns. Superphosphate is gradually decomposed in the soil, providing soluble phosphorus which is absorbed by roots and translocated within the plant. It is ideal for feeding root vegetables such as carrots and beetroot it also assists seed germination. 
Sulphate of Ammonia - A rich nitrogen fertiliser for healthy green leaf  growth for plants and greening lawns. It is fast acting and gives quick visible results. It can be used dry or made into a liquid fertiliser. Precautions: Wash any fertiliser off foliage and water in well if applying dry.
Sulphate of Potash - Is a rich source of potassium for encouraging flowering and fruiting in all plants, as well as promoting disease resistance. It improves flower and fruit quality and is ideal for mixing with Blood and Bone for an organically based complete fertiliser