With so many different types of fertilizers available for garden plants, the choice can be a little confusing. Each type is made for particular plant growth needs. Many gardeners use a number of different fertilizers during the year. An all-purpose type is effective for basic gardening, but some plants, such as cacti or orchids, have particular needs and benefit from a specific fertilizer.

However, there are really two main types of fertilizers; including both organic and inorganic fertilizers.

  • Organic fertilizers are those made from purely natural processes and ingredients, including seaweed, worm castings, manure and other products.
  • Inorganic fertilizers are made by a chemical process and include many of the popular ‘slow release fertilizers’ used in gardening.

How do fertilizers work?

Fertilizers can be broken down into liquid and solid types of fertilizer, both having their advantages. All fertilizers are designed to provide plants with essential nutrients to help promote healthy growth.

Many inorganic and organic types of fertilizers are defined by the ratio of NPK. This is the ratio of the elements Nitrogen (N), Phosphorus (P), & Potassium (K).

  • Nitrogen helps promote Foliage Growth (leafy growth)
  • Phosphorus is for the Roots and Flowers
  • Potassium (Potash) is for general plant health; promoting flowering and fruiting and helping to prevent diseases

Slow release type fertilizers, are generally inorganic and are designed to release nutrients over a period of time, generally three to nine months.

Fish and Seaweed Fertilizers

  • Fish Fertilizer is a widely used type of organic ftype.
  • Fish fertilizer is said to increase microbial activity in the soil, as well as to encourage earthworm activity
  • Fish fertilizer provides an excellent, easily available source of nitrogen for plants. It is a favorite with tomato growers who often use it every 2-3 weeks to promote growth
  • When combined with other type such as Seaweed fertilizers and extracts, efficiency is improved
  • Seaweed or Kelp is another organic product that has been used in gardens for hundreds of years. Readily available in both liquid and powder form, Seaweed fertilizer contains many of the important nutrients required to promote healthy plant growth.
  • Seaweed or Kelp is used to promote seed germination and promote root growth in new plants. Seaweed or Kelp also is said to assist with the uptake of nutrients.

Rock and Mineral Fertilizers

These are a little different to most fertilisers. They are naturally slow release, organic and do not leach from the soil. They improve soil condition and enhance microbial activity.

They are make from a range of different rocks and provide a range of different minerals depending on the rock used. They are often used in conjunction with other types of fertilizer.

How to Use of Fertilizers

Plants will alert the gardener that more nutrients are needed to allow healthy growth. Watch foliage for signs of lack of nutrients.

  • Leaves turn yellow when nitrogen is deficient.
  • Leaves will turn purple or red if they don’t have enough phosphorous.
  • A lack of potassium will cause older leaves to burn and drop.
  • Nutrient deficiency is also indicated by weak or slow growth and smaller leaves and flowers.
  • However, other factors such as lack of light, over watering and temperature changes can also cause similar symptoms so make sure you eliminate these factors first, so you don’t over fertilize your garden plants.