Notes on some commonly used organic ferts:
Blood Meal : 13 - 0 - 0
Blood meal has one of the highest concentrations of Nitrogen of any organic fertilizer, and is consequently a popular choice for the vegetative growth period. In its dry and slow-acting form, it can be mixed in with the soil at a rate of 1 to 2 tablespoons per gallon of soil mix. However, many growers prefer to use it as a soluble fertilizer as it acts very quickly without much danger of burning - much like the action of a chemical fertilizer, but without the risks.
To make blood meal tea, soak 1 tablespoon of blood meal in a gallon of water for 5 to 7 days. The longer you wait, the higher concentration of N the tea will have. Shake well, then strain out the solids and water your plants with the tea.
Bone Meal : 1 - 11 - 0
Bone meal is high in Phosphorus, and is most suitable for the flowering period. However, as it is a slow-release fertilizer, it is fine to add to the soil earlier in the grow period. (Perhaps the best course of action is to add it to the mix you perform your final transplant into.) One caution about bone meal, especially in Europe, is that many growers will not use it for fear of spreading Mad Cow Disease. Although this has not been proven, it is wise to bear this in mind.
Fish Emulsion : 5 - 1 - 1
Fish emulsion is a liquid solution made from decomposed fish and sometimes other ingredients. It is an exceedingly gentle fertilizer and is thought by many growers to be the best "first fert" to use on young plants. Its NPK ratio is also ideal for vegetative growth. It is usually mixed with water at a rate of 1 to 3 tablespoons per gallon.
Worm castings : 0.5 - 0.5- 0.3
Also known as worm compost or good ol' worm sh*t, this may be the single best all-purpose fertilizer. Although the nutrient levels are relatively low, worm castings somehow have amazing effects on plant vigor, and anyone who has used them can testify to their effectiveness. They are very gentle on plants, making them ideal for seedlings, and also contain micronutrients. Worm castings can be used as part of the soil mix (no more than 15% total volume is suggested) or can be made into tea (1 part WC to 5 parts water) and applied as watering solution or as a foliar fertilizer.
Kelp meal: 1 - 0.5 - 2.5
Kelp meal provides over 60 trace elements, plus growth promoting hormones and enzymes. As such, it is often used to ensure the plant is properly supplied with micronutrients. Can be used as part of the soil mix (1-2 tablespoons/gallon) or brewed into tea at the same rate.