If your finding it difficult to choose the right Fertiliser for your landscape jobs, we have the information to help you choose. Robert Megier from Everris Australia has kindly answered all of these questions to make it a bit easier for you.

What is an organic fertiliser?

In scientific terms, an organic compound is anything that contains carbon regardless of its source. In fertilisers, it has come to mean fertilisers from a natural source such as manures, composts, seaweed extracts, etc. Organic fertilisers are often not very cost effective if just measuring the nutrients provided but they can provide other advantages such as improving soil structure and microbial activity.

What’s this soil structure and microbial activity actually do? How do these organics help? What circumstances will they be of benefit?

Soil structure is referred to as the physical characteristics of the soil and microbial activity is referred to as the biological characteristics of the soil. Both are important to encourage good root development and therefore plant establishment. Organics will add organic matter (carbon) to the soil which can be particularly helpful in marginal soils such as very sandy soils or clay soils.

What is a compound fertilizer?

A compound fertiliser is one that has several elements included. Typically they contain nitrogen, phosphorus and potassium but few if any trace elements. They have no slow or controlled release characteristics other than the speed at which they dissolve. An example of a compound fertiliser is No. 17 Lawn Food.

Where would you use a compound fertiliser?

You would use a compound fertiliser where you want a quick, short term response. Typically you will need to irrigate after application to dissolve the product and avoid burning of foliage or turf.

What is a slow release fertiliser?

Organic fertilisers can be slow release due to their microbial activity. Inorganic slow release fertilisers are usually granular and they rely on the action of water (hydrolysis) or microbial activity, or both, to release their nutrients. Often only some of the nutrients (usually nitrogen) are actually released slowly. They typically have longevity of no more than 3 months. Examples of slow release fertilisers are Lawn Builder and Agriform planting tablets. See http://www.everris.com.au/landscape/nutrition/garden_planting_and_maintenance/agriform.html

What is the benefit of using slow release over organic?

There is a cost benefit of using slow release over organic fertiliser. The nutrient content of slow and controlled release fertilisers is much higher per unit of weight compared to organic fertilisers.

What is a controlled release fertiliser?

A controlled release fertiliser is typically a coated, prilled product. Each prill can contain either a single element or a complete range of major and trace elements.  The rate of release is “controlled” by the temperature and hence the name controlled release. Stated longevities are matched to average temperatures. For example, a product that states 8-9 month longevity at 21°C is likely to last 10-11 months at 16°C and 4-5 months at 31°C average temperature (day and night). Examples of controlled release fertilisers are Osmocote and Sierrablen: http://www.everris.com.au/landscape/nutrition/garden_planting_and_maintenance/sierrablen_flora.html

How does a controlled release fertiliser work?

Water penetrates through the semi-permeable coating and dissolves the nutrients inside the prill. The dissolved nutrients are released through the coating due to differences in osmotic pressure inside and outside the prill. The rate of release is influenced by temperature but not by soil pH, microbial activity, water quality or rainfall.

What are the benefits/downsides of using controlled release fertiliser compared to slow release or compound fertilisers?

Controlled release is the most technically advanced product and will give the greatest amount of control over the release of fertiliser. It is also able to provide the greatest longevity of release of all the fertiliser types. It will be of greatest benefit where the organic matter and cation exchange capacity of the soil is low. It is also the safest of all the products with no chance of adding excess salts if used as per the label instructions. The downside is that it is more expensive than the other forms of fertiliser.