By Kate Wall
We are aware of the need to fertilise lawns, but choosing a fertiliser is not always easy when there are many products to choose from. While there are many brands available, each making their own claims to greatness, understanding the basic types of lawn fertiliser and when they might be best used will help narrow the choice.
All commercially available fertilisers are required to display the nutrient analysis on the packaging. This is often reduced to the N:P:K ratio, which is the ratio of the 3 major plant nutrients; nitrogen (N), phosphorous (P) and potassium (K). Other important plant nutrients such as calcium, magnesium, manganese, iron and sulphur are also listed on the packaging if they are present.
Nitrogen is required for producing green leaves in plants. In a lawn nitrogen is important as the green leaf is the part which is regularly cut and removed when mowing, and the part which needs replacing if the lawn is to remain green. Lawn fertilisers are therefore usually fairly high in nitrogen. Phosphorous and potassium and the other major and minor plant nutrients are also required to allow for root development, plant strength, good health and disease resistance. Complete lawn care will be best achieved by providing a range of nutrients, not only nitrogen.
Fast Acting vs Slow Release
In general, a fast acting fertiliser will give a very quick flush of new green growth but that flush will not last long. By contrast a slow release fertiliser will not give such impressive instant results, although it will give reasonably fast results in a lawn. The great benefit of a slow release fertiliser is in its ability to deliver a small but constant feed over a period of months instead of weeks. This gives improved growth which is sustained over time as opposed to instant but short lived results. Slow release fertilisers are almost always better value for money, and give better results for your lawn. If a fertiliser does not say slow release on the label, it is likely not. Usually fast acting fertilisers are in powdered or very small pellet form. Slow release fertilisers are usually in the form of granules which dissolve and therefore release their nutrients more slowly.
An exception is organic fertilisers. Organic fertilisers are in plant safe forms and bound into organic matter which is naturally a slow release form of fertiliser, even if this is not stated on the product.
High Nitrogen Fertilisers
All high nitrogen fertilisers have the ability to burn sensitive plants and even lawns if used too heavily. Excess of nitrogen without sufficient balance of other nutrients can cause fast green growth which is weak and prone to drying out as well as pests and diseases. While nitrogen is required for a healthy lawn, a complete and balanced fertiliser is recommended for healthy plants and better long term results.
Organic fertilisers are usually in the form of pellets based on composted chicken or other animal manure. These fertilisers have the nutrients bound in organic matter which plays an important role in improving soil health and structure as well as providing nutrients to plants. The nitrogen level in these fertilisers is generally quite low (below 5%) and therefore there is almost no risk of burning the grass through over fertilising. These fertilisers work well on lawns, however they do often lack the complete balance of nutrients required for healthy plant growth and are best supplemented with either rock minerals or a balanced inorganic fertiliser occasionally. Some of the more expensive brands such as Seamungus or Eco88 contain additional sources of organic plant food and have a greater range of major and minor plant nutrients contained within the one product.
Blood and bone is another type of commonly used organic fertiliser. Nitrogen values in blood and bone vary between brands but can be surprisingly low. Blood and bone is a good source of phosphorous but contains no potassium.
Most organic fertilisers can be smelly for a day or so and in this time can be highly attractive to dogs. This can result in dogs digging in the lawn or garden and eating the fertiliser and becoming sick. They are best used when there is rain to water them in well or when there are no dogs around. An exception is to use rock minerals, usually available from produce stores or specialists rather than major hardware chains. Rock minerals products vary but usually contain a huge range of different major and minor plant nutrients as well as trace elements which not only enhance plant growth, but also greatly improve soil health. They can be used in combination with other fertilisers to increase the effectiveness of other fertilisers.
Inorganic fertilisers come in different forms and can be powders, pellets or granules. As these fertilisers are chemically produced, they have a repeatable and known chemical composition, which will be stated on the packaging in the nutrient analysis. Inorganic fertilisers can have high nitrogen levels (above 10%) and can often also have high salt levels, which can burn plants and lawns if applied too heavily. Err on the side of caution and use small amounts. Repeat the fertilising process a month or two later rather than apply more in one dose to reduce the risk of burning.
Dog owners often prefer using inorganic fertilisers as they are not attractive to dogs.
Inorganic fertilisers often have a handful of key plant nutrients contained within the formulation, not just the basic N:P:K. It is rare however that they will have a very large range of the smaller trace elements which are also required by plants. Each brand has a different make up of major and minor plant nutrients, and for this reason many lawn lovers will use a different brand regularly to provide different minor nutrients each time.
Inorganic fertilisers can be slow release and dissolve slowly to release nutrients to the lawn over many months. They do not contain additional organic matter or microbes and therefore offer no soil improvement.
A cross over product is called Lawn Blend by Earthlife. It contains inorganic lawn fertiliser in combination with rock minerals. This product therefore addresses the need for many different major, minor and trace nutrients, as well as giving significantly improved soil health.
For more information on Inorganic Fertilisers click here.
Weed and Feed
Combination products are becoming very popular as they are advertised as very easy to use. These products contain a broad leafed herbicide to kill broad leaved weeds in lawns at the same time as delivering a fast acting liquid fertiliser. Their effectiveness can be very variable as they can be unstable and degrade in hot conditions. It is often found that by fertilising the weeds at the same time as poisoning them, the weeds are better able to resist the poison and this not only does not effectively kill the weeds, but also assists them to develop resistance to the herbicide used. For this reason it is highly recommended to weed and feed a lawn as separate tasks.
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