By Kate Wall
For information on different types of fertiliser and when each are suitable, please click here. Once you have decided that you wish to use a slow release inorganic fertiliser, there are still many different products available to choose from. This review will assist you to narrow your choice.
A slow release fertiliser feeds your lawn over a period of months. Just how many months will be dependent on the product and on local weather conditions. All fertilisers are designed to work in ideal conditions. Too much or too little water will affect their performance. In dry conditions the fertiliser will not dissolve and will be releasing less nutrient to be available to the lawn. Too much water can cause the fertiliser to dissolve more quickly or even wash away, shortening the time the nutrients are available. Both scenarios will cause lawns to be stressed. Stressed plants are not able to take up fertiliser even if it is available, so good lawn care which ensures the lawn is not under stress will greatly assist the uptake and effectiveness of any fertiliser applied.
Some fertilisers are developed for use on buffalo lawns. These are perfectly fine to use on all lawn types, however when it comes to weed and feed type products as opposed to fertiliser only products, it does matter. The weedkiller used in weed and feed products for non-buffalo lawns has the ability to severely damage a buffalo lawn, so when it comes to weedkillers, choose according to your lawn type.
Understanding the N:P:K ratio on fertilisers
In general lawn fertilisers are designed to be high in nitrogen (N), as nitrogen is the nutrient required for healthy leaf growth. With regular removal of green leaf from lawns (mowing) nitrogen is required to help keep the lawn green. In small amounts the minor nutrients iron (Fe) and sulphur (S) also play a role in keeping the lawn green. Fertilisers which are very high in nitrogen and very low in everything else will tend to cause a flush of green growth which is sweet and tender and highly attractive to pests. High nitrogen levels which are not in slow release form can often be washed out of the soil before the lawn can use it and cause problems in our waterways.
P is the symbol for phosphorous which is required by plants for strong root growth. A strong lawn needs strong roots and therefore does need phosphorous. Phosphorous is not readily leached from the soil (as is nitrogen) and therefore is not needed in large amounts. Most lawn starter fertilisers have some phosphorous to assist in root growth of the new lawn but phosphorous is very low or lacking in most lawn fertilisers. Choosing a fertiliser with a small amount of water soluble phosphorous will be beneficial to your lawn.
K is the symbol for potassium, which is required for thicker cell walls and stronger more diseases and pest resistant plants - including lawn grasses.
Other minor plant nutrients and trace elements are sometimes included in lawn fertilisers and will ensure a more complete and well balanced feed for your lawn. It should be noted that most problematic lawn weeds prefer calcium (Ca) deficient soils, so by selecting a fertiliser which includes some calcium, not only will your grass be healthier with this essential plant nutrient, but the weeds will be disadvantaged.
Fertilisers which contain organic matter, high silica, humic acid, bio stimulants, or soil microbes will all assist with improving the soil in addition to feeding the lawn. A healthy soil also contributes significantly to the overall health of the lawn, therefore fertilisers which assist with soil health should be considered above those which lack any of these additional organic inputs. Artificial wetting agents can be beneficial in poor soils, however all of the organic inputs mentioned will also act as wetting agents in addition to improving the soil.
It should also be considered that a high nitrogen fertiliser is more likely to burn the lawn when used heavily, especially in hot weather. The presence of soil microbes and other organic inputs will reduce the risk of burning, or of salt build up.
The table below gives a summary of the nutrient make-up of the major lawn fertilisers available in hardware chains, and also includes some which are only available in produce stores, nurseries or online.
Of the high nitrogen fertilisers which are designed for frequently mown or high use lawns, Ozbreed is the only one which also contains significant trace elements and humic acid (organic matter) therefore contributing to the overall health of the lawn, rather than simply causing green growth. These fertilisers are true slow release fertilisers and will not burn the lawn when used in the right dose rates. The Ozbreed fertilisers are formulated with different N:P:K ratios to best support lawn growth at different times of year, giving consideration to what the lawn needs at different times. The formulation into season labelled products makes this easy for the gardener to know which to apply when, aiding the lawn lover to get the best possible fertilising program for their lawn. The Ozbreed fertilisers are available online here
The Earthlife and Troforte lawn fertilisers are the only ones which offer a very complete range of trace elements as well as soil microbes. These products will both be highly effective soil improvers in addition to good lawn fertilisers, and will play a role in reducing the incidence of pest, disease and weed problems. Both are available through produce stores, nurseries and online.
The remaining fertilisers compared below are all available readily through major hardware chains. Of the products compared, the Scotts Lawn Builder with Organics is the most complete product in the range with trace elements and organic matter. The other fertilisers will help with greening and lawn growth but will not give as much long term health to frequently mown lawns. The Yates Dynamic Lifter Lawn Starter will be highly beneficial to lawns which are not high use or do not get mown frequently.
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