Fertilizers are used to supply extra nutrients to growing plants when needed. They are applied in two ways, either before planting or sowing as a base dressing, which is raked or forked into the soil, or as a top dressing, which is sprinkled around the growing plants, or, if in liquid form, applied with a watering can around the base of a plant.
Plants need the following nutrients plus some trace elements to grow.
NITROGEN — N This is important for leaf growth, so brassicas require large amounts of nitrogen.
PHOSPHATE — P This is necessary for root growth and for young plants and new shoots.
POTASH — K This aids the production of flowers and fruit and keeps plants healthy.
To provide supplies of one or all of these nutrients you can use a chemical or organic fertilizer.
These can contain one major nutrient or are a compound, a balance of all three. They are easy to use, produce quick results and promote high yields but organic growers would argue that flavour suffers and plants are more prone to pests and diseases. Furthermore, artificial fertilizers do not put anything back into the soil itself for the next generation of plants.
These are usually gentler in action and so there is no danger of giving plants too much, which can occur with a chemical fertilizer.