Which fertiliser provides best value?

Controlled Release Fertiliser

What is the difference between the many Controlled Release Fertilisers available these days? How do we work out which one gives us the best value?

There are many controlled release fertilisers available these days, and it has become somewhat confusing for the grower to decide which product to use to achieve the best overall outcome in nursery production. It is definitely a case of the cheapest NOT necessarily being the best. The cost of the fertiliser in the production of a quality plant is very small, and only very small benefits are required to make it worthwhile using a more expensive fertiliser. It is very important for growers to trial the different products for the full growing cycle to see which product gives them the best results in the number of saleable plants in the shortest time with the least amount of labour inputs.

As an example:
An 8mth release fertiliser, which is commonly used for 140mm nursery stock, is used at around 5kg/m3. Therefore, one 25kg bag will be sufficient for 5m3 of growing media. A 140mm pot requires around litre of growing media, so this one 25kg bag is going to feed 5000 x 140mm plants. These generally wholesale for around $5.00, so one bag of fertiliser is going to produce $25,000.00 worth of stock. As you will see, to pay an extra $20-$30 for a quality fertiliser can easily be made up in better results.

  • If there are more than 6 extra 'saleable' plants in any 5000, the grower is in front.
  • If the crop is ready for sale 1 week earlier, the grower can earn/offset $25 in interest (@ 5% rate) with the earlier sale.
  • If the fertiliser grows a better more robust plant with less labour input of pruning etc., only 2 hours of labour needs to be saved (maintaining 5000 plants) to be in front.

It only requires ONE of the above scenarios to make it worth paying extra for a quality fertiliser; a premium quality fertiliser will combine ALL these benefits at greater quantities than mentioned, which puts the grower way in front financially by using a quality fertiliser.

What makes a 'quality' fertiliser? Many things . . .

  1. THE INGREDIENTS: The nutrients which make up a fertiliser are available in many different forms. To be available to the plant, they must firstly be soluble enough to be released through the very small openings in the coating, and secondly, they need to be in a form that is easily 'available' for the plant to take in through the root system. Higher grade, more soluble ingredients cost more, so most cheap fertilisers use cheap ingredients. It is also important to make sure that the trace elements are included at sufficient levels to meet the plants requirements; while the NPK is clearly displayed, most products are marketed as just 'plus trace elements' - many cheap fertilisers have low levels, or an incomplete range, of trace elements.
  2. THE COATING: Many different products and methods are used to achieve a 'Coated Controlled Release Fertiliser'. A quality fertiliser will have a coating that will maintain its integrity in any of the varying situations which apply to the production and use of growing media; it must be durable enough to withstand the media blending process without damaging the coating; it must be flexible enough to withstand packing, shipping, and being dispensed through a potting machine without cracking the coating; it must be able to sustain the effects of high temperatures without the excessive release of the nutrient; and it must provide even and consistent release of nutrient throughout the growing period.
  3. THE RELIABILITY: The grower must be able to depend on the results being consistent for every production run. Therefore the fertiliser manufacturer MUST have a proper QA system to ensure that all product released for sale will perform in a consistent manner.