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When should I fertilize my lawn?

If you need to fertilize, the following are some suggestions:

  • Fertilize with slow-release fertilizer from mid-August to mid-September, then late October to early November, followed by late Spring.
  • Apply less fertilizer in the spring and early summer than in early and late fall.
  • Organic fertilizers release more nutrients as the temperature and moisture levels increase. Avoid fertilizing when conditions are likely to be hot or dry, usually from mid-June to early August.
  • Your Naturally Green Calendar ( Adobe Portable Document Format (PDF) 3MB) is a guide to the best times to perform lawn maintenance activities.

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Types of Fertilizer

Use Phosphorus-free Fertilizers

The overuse of phosphorus fertilizers causes toxic algae blooms , which negatively impact marine plants and

Help protect our local lakes, rivers and streams and use a phosphorus-free fertilizer. Only use a fertilizer with phosphorus if:

  • You have a newly seeded lawn.
  • Your soil has been tested and results show a phosphorus deficiency.

For more information on phosphorus and algae visit Halton's Lake Ontario Shoreline Algae Action Advisory Committee (LOSAAAC) page.

  • Finished compost is a great fertilizer that supplies your lawn with nutrients needed for plant growth.
    • Compost can be applied at any time of the season.
    • Mix compost into the soil before seeding or laying sod.
    • Spread a thin layer over the existing lawn.
  • Commercial fertilizers usually contain three major nutrients:
    • Nitrogen (N) to promote leaf growth
    • Phosphorus (P) to promote root growth,
    • Potassium (K), which is essential for stress resistance.
    • The three numbers on the packaging represent the proportions of these nutrients.
      For example, 21-7-7 formulation contains:
      • 21% nitrogen
      • 7% phosphorus
      • 7% potassium
    • Fertilizers with a slow-release form of nitrogen are preferred because they release nutrients slowly and there is less risk that excess fertilizer will leach away from the root zone.
    • All purpose turf fertilizers usually have a 4-1-2 N-P-K ratio.
    • Rates and timing of fertilization can vary with the type of soil, grass, site and weather conditions.

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Combination Products

  • Combination products containing a herbicide and a fertilizer (weed and feed type) should only be used if your lawn has a widespread weed problem and a nutrient deficiency.
  • If you choose these combination products, use according to directions.
  • Check with your local municipality regarding by-laws regulating the use of these products.

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Analyze your soil

  • Have your soil analyzed every few years by a professional laboratory.
  • This will tell you what type of fertilizer you may need and how much to use. It will also indicate if the pH of your soil is ideal for growing grass.

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