Many novice gardeners never use a lawn fertiliser or use them incorrectly.

But fertilising your lawn needn’t be complicated.

I’m going to explain what lawn fertiliser is and how to keep your lawn healthy and green with minimal effort.

What is Lawn Fertiliser?

Lawn fertiliser, also known as lawn feed, is thought of as food for grass plants.

In actual fact, fertiliser products whether they are granular, or liquid based contain the chemical elements plants need to make food through photosynthesis. These important chemicals include:

Nitrogen (N)

  • Important for the formation of cells and stimulating grass growth
  • Helps create chlorophyll (which makes grass green) which is used in photosynthesis
  • Promotes healthy flowering and seeding
  • Improves the quality of root development and overall lawn health

Phosphate (P)

  • Required in the production of food
  • Important for healthy grass growth
  • Promotes strong root development

Potassium (K)

  • Helps in the creation of plant cells
  • Important for photosynthesis and other plant functions
  • Increases the cold and drought tolerance of grass
  • Is sometimes lacking in soil

The contents of all fertiliser products are shown as NPK values on their label. Learn how much lawn feed to apply.

Why Fertilising Your Lawn is Important

Time causes nutrients to be removed from soil.

If these nutrients aren’t replaced, the health and quality of your lawn will decline over time.

What Happens to a Lawn Starved of Nutrients?

Without a constant supply of nutrients, grass plants cannot function properly. Food production slows which causes growth to slow and leads roots to weaken.

Eventually grass will turn yellow or brown as it begins to die and is overcome by lawn disease.

Your lawn will become thin and patchy and weeds will grow in the absence of grass.

Why Do the Nutrients in Your Lawn Decline?

Nutrient decline is caused by two things;

  1. You Remove Them Every Time You Cut the Grass

Grass and other plants use photosynthesis to make food from water, carbon dioxide and the ingredients that are found in fertiliser.

Water on the surface of your lawn and in the soil dissolves the fertiliser. This allows grass to absorb these nutrients via its roots. Food is then produced and stored in the leaves of each plant.

Every time you cut the grass, water and nutrients are removed from the top layer.

If you cut the grass often and mow it to the correct height, the decline in nutrients will be gradual. If you let it grow long and then mow it too short, these nutrients will be removed as well as most of the water stored within the plant. This can devastate any lawn.

Those with a mulching lawn mower can mulch grass clippings back into the lawn. This helps recycle lost nutrients and slow their decline.

  1. They Get Washed Away by Rainfall

Water is important to the health of your lawn as it helps transport the nutrients in fertiliser into the grass plant.

Unfortunately, heavy rainfall can wash these nutrients away.

The result is the onset of lawn diseases like rust and fusarium patch.

Granular Fertiliser
Granular Fertiliser

Different Fertilisers for Different Seasons

Grass needs nitrogen, phosphate and potassium to grow.

More importantly, your lawn needs different amounts of each nutrient at different times of the year. Using the wrong type of fertiliser at the wrong time of year can do more harm than good.

Spring / Summer Fertiliser

During the spring and summer, your lawn is growing quickly and producing flowers and seed heads.

At this time, it needs a feed with plenty of nitrogen and potassium and a little phosphate.

Autumn / Winter Fertiliser

During the colder, wetter months of autumn and winter, grass growth and food production stops.

Instead of growing new leaves, grass plants focus on strengthening their roots.

The result is that they don’t need as much nitrogen. A good dose of potassium will help build thicker cell walls and increase the plant’s tolerance to cold weather.

The Danger of Applying the Wrong Fertiliser at the Wrong Time of Year

Applying the wrong fertiliser at the wrong time can have undesirable effects on your lawn.

If you apply a spring / summer lawn feed in autumn or winter, the large dose of nitrogen can cause the grass to surge in growth which is unsustainable. This rapid growth comes at the expense of tolerance to cold and wet weather, making grass more susceptible to disease.

Applying an autumn / winter feed in the spring or summer starves the grass of nitrogen and phosphate. This results in a grass plant that isn’t as strong and dense at it should be which increases the likelihood of weed seeds germinating in your lawn.

Final Verdict

Lawn fertiliser can be broken down into two types;

  • Spring and summer
  • Autumn and winter

You only need to apply lawn feed four times a year to maintain a lush, green and healthy sward. Take a look at our lawn feeding schedule for a detailed guide covering when to feed your lawn.

It’s also a good idea to learn how to feed your lawn with a granular fertiliser and how to apply liquid lawn feed properly for maximum efficiency.