My Lawn Is Full of Weeds

Updated November 21, 2016

Lawns full of weeds may indicate underlying issues. Over-fertilising, low mowing heights and thick thatch build-up contribute to an unhealthy yard. Fixing these problems will help reduce future weed problems, yet you must remove your current weeds to help restore the lawn. Weed identification is also imperative when selecting the right herbicide to use.


Gardeners often fertilise their lawns before their grass has had time to green up for the growing season. Because the lawn is still in dormancy, grass cannot use the fertiliser. Instead, weeds absorb the nutrients and start spreading throughout the yard. Without competition from the grass, weeds are free to germinate seeds and impede dormant grass. Wait until after two to three weeks of grass growth to apply fertiliser to the lawn. Use the right amount of fertiliser for your grass type. Typically, 0.454kg. of fertiliser should be applied every 1,000 square feet.


Cutting your grass too short will cause weak root systems. Grass with weak root systems cannot spread or compete with weeds for the soil's nutrients. All grass varieties have their own mowing height requirement. For example, tall fescue should be kept at 2 inches during the fall and spring. Raise your mower's blades in the summer to keep tall fescue at 3 inches in height, according to Texas A&M University. Never take off more than one-third of the grass blade, because it will result in weak roots.


Thatch is the interwoven organic material that sits between your grass and soil. A thatch build-up of more than 1/2 inch can encourage weed growth. A thick layer of thatch prevents proper air circulation and absorption of fertiliser and causes fungal disease. Before weed removal can begin, gardeners should dethatch their lawn. You can rent a dethatcher from your local gardening supply store. After your remove thatch, you may notice bare areas in the lawn. Seed those areas before weeds take advantage of bare soil.

Choosing Herbicide

There are two types of herbicides that you can use: broad spectrum and selective. Broad spectrum will kill any vegetation that it comes in contact with. Selective herbicide is chemically formulated to kill only specific types of weeds like grassy weeds, sedges or broadleaved. These herbicides can be safely used within you lawn. Identify the weeds growing in your lawn. Sedges have rounded tips, grass has triangular tips and broadleaved weeds are more colourful. Choose a herbicide that kills your weed type.

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