What is Lawn Fertiliser

Having a basic understanding of your lawn care fertiliser is a good thing. You can take it to the extreme and make life very complicated, so, unless you are after a degree in agronomy or green keeping I suggest the basics will do nicely.

Lawn fertiliser products are not food as such but the basic chemical elements required by plants to make food. Photosynthesis (means making things with light) is the process where sun light is used to make starches and sugars (food) from carbon dioxide (CO2), water and your lawn feed. Soil water dissolves these fertiliser nutrients enabling them to be taken up by the roots. The availability of sun, CO2, water and fertiliser has a big impact on the grass plants. Carbon dioxide and sun light are pretty much out of your control but are readily available and, in a good year, sun shine is plentiful. Water is also somewhat out of your control; you may be able to turn the hose pipe on but you can’t stop it raining!

This leaves us with the mineral nutrients (fertiliser) as the factor that can be controlled and may be in short supply. Not all nutrients may be short as the soil; clay, silt, sand, age, organic content, treatment, location and living content (bacteria, fungi, insects, worms etc) will all impact nutrient levels. One thing is certain; the primary nutrients (used in all plant processes and structures) will need to be added because you mow the lawn thereby removing masses of plant material AND stored food.

Primary Nutrients:

Nitrogen (N)

• Important for cell formation and therefore grass growth
• Forms part of chlorophyll (the green colour) so important in photosynthesis
• Important for flowering and seeding
• Improves lawn health and root growth
• Can be lost from the soil into the air or washed out by excessive rain
• Grass needs a regular supply either by frequent applications or by slow release ‘trickle’ feeding

Phosphorous (P) or Phosphate

• Essential for food production
• Assists in grass growth
• Encourages rooting – will also assist weed seeds to root!
• Excess use can cause build up of thatch
• Organic forms (manure) can be washed into waterways causing algal bloom
• Organic, loam or clay soils may well contain adequate long term supplies
• Some turf professionals apply very little phosphate for the above reasons
• Lawnsmith fertiliser programmes for clay and sandy soils vary for some of these reasons

Potassium (K)

• Helps build plant cells
• Involved in photosynthesis and plant functions
• Control stomata which control water within the plant – affects drought tolerance of your lawn
• Quite mobile in soil so needs regular applications

Secondary Nutrients

Though these are far less in demand by the grass compared to Primary Nutrients they are still essential and rarely incorporated into lawn feed due to cost. Therefore if you find a fertiliser with these components then grab it quick. Sulphur used to be abundant due to coal burning fires but today with smokeless fuels there is far less in the environment and is now often deficient in soils thus the need to add as part of your lawn care feeding program. An annual dose or two of iron or ferrous sulphate in solution, as a turf hardener and tonic is one way to see that the grass gets an adequate supply of both iron and sulphur.

• Calcium – essential part of plant cell structure
• Magnesium – associated with photosynthesis, chlorophyll (and therefore colour) and plant functions
• Sulphur – used in proteins within the plant:
  • Promotes formation of enzymes, chlorophyll and vitamins
  • Helps in growth and resistance to cold
  • Also involved in root growth and seed production

Trace Elements

There are other essential elements such as iron, boron and zinc which are normally found in adequate levels in most soils. An occasional feed with a fertiliser containing seaweed usually keeps the lawn well topped up.