Lawn & Yard Weeds

Healthy grass is tough, resilient and able to out-compete most weeds. Good turf management is based on the approach that some weeds are beneficial. For example:

  • Daisies or dandelions look attractive and can attract beneficial insects to the garden
  • Weeds with deep roots, like White Dutch clover, break up compacted soil and bring nutrients to the surface

Here are tips and techniques to minimize lawn and yard weeds.

Mowing Practices

Mowing is the key to weed control:

  • Mow to a height of 6 - 8 cm – this will help:
    • Grass roots to grow stronger
    • Prevent fallen weed seeds from germinating
    • Your lawn be more resistant to fungal diseases or drought
  • Mow often with a sharp blade – it's best to clip small amounts frequently (less than a third of the length)
  • Leave clippings on the lawn as fertilizer (except for long clippings)

Fertility

Weeds common to turf are indicators of poor fertility, compacted soil and either droughty or waterlogged conditions. Provide proper nutrition to give your lawn a competitive advantage:

  • Use slow release fertilizers or top-dress every year or two with good quality compost
  • Do not over fertilize with soluble nitrogen – this stimulates soft, lush growth which is more susceptible to disease, contributes to the build up of thatch and makes more frequent mowing necessary
  • Have the soil acidity (pH level) tested by a garden centre – apply dolomitic lime as needed to maintain levels between 6.5 and 7.0

Watering

  • Water turf deeply, but not often
  • Soak to the root zone (about 6-8 cm deep)
  • Don't water again until the top 2 cm of soil has dried out
  • Do not over water – this will create waterlogged conditions that kills grass roots and leaves room for weeds to become established

Aerating

Compacted or heavy clay soils may need to be aerated mechanically every year or two:

  • Rent a lawn aerator for large areas or, for smaller lawns, repeatedly spike the soil at a slight angle with a garden fork
  • After aerating, top-dress the turf with fine sand (0.25-1 mm) from a gravel company – this is especially recommended to improve drainage and aeration for heavily-used lawns

Thatching

Thatch is the layer of un-decomposed organic material that accumulates at the base of the grass plants. Some thatch is beneficial – it shades roots and reduces water loss. Thatch should be removed if the layer becomes more than 1 cm deep – grass begins to root in thick thatch rather than the soil, making it more susceptible to diseases, bugs and drought. Thatch is naturally removed by earthworms – rakes and thatching equipment are also useful for manually removing it.

Earthworms

Thriving earthworm populations are important for healthy lawns. They burrow in the soil and break down the thatch layer and other organic material, turning it into rich fertilizer. They mix this fertilizer deep into the roots and aerate the soil. Rake or scatter large accumulations of earthworm castings that become visible.

Weeding

Well-established rosettes of dandelions, thistles and plantain lie low enough to be missed by the mower and must be removed:

  • When the soil is moist, dig out the entire root using a sharp weeding tool
  • If a large weed leaves a gap, level the soil and sprinkle grass seed into the bare spot
  • Longer mowing heights and improved lawn care will prevent new ones from becoming established

Seeding New Lawns

  • Have a soil sample tested for pH levels and fertility
  • Prepare your soil type according to local recommendations for proper liming, fertilization and compost
  • Choose an appropriate seed mix for soil type, shade or sun, heavy or light use, etc.
  • Consider incorporating varieties of perennial ryegrass or fescues with endophytes (beneficial funghi) in the seed mix, because of their increased vigour
  • Include a small proportion of white Dutch clover in the mix on poor or compacted soils – it stays green, resists drought, increases soil fertility and breaks up compaction
  • Stimulate weed seeds to germinate before planting – prepare the soil, wait for two weeks to allow weeds to germinate, then repeat the process
  • Seed the lawn after the second or third "weed seed" germination and cultivation cycle

Grass with Endophytes

Endophytes are fungi that can benefit grass by producing toxins that kill or repel insects and provide some resistance to disease. Turfgrasses with endophytes are generally more vigorous, more tolerant of heat and drought and more competitive.

  • Check turf seed suppliers for varieties of perennial ryegrass and fescues with high levels of endophytes
  • Make sure seed is fresh because endophytes may die after prolonged storage
  • Do not plant endophyte-infected grasses where horses or other grazing livestock may eat it

Change the Site

Some areas are weedy because grass will not grow well there:

  • In shady areas, like under a large tree, consider using shade-tolerant groundcovers, bark mulch, gravel, stones or pavers laid over landscaping fabric
  • Heavy traffic areas or "short-cut" paths can become weedy because of compacted soil – try:
    • Changing traffic patterns using fencing, hedges or other barriers
    • Mulching or paving the pathways
    • Laying turf blocks – hollow concrete pavers that allow grass to grow in the centre

Weed Prevention

Reduce the number of weed seeds entering your yard:

  • Watch for flowering weeds along roads, driveways and fence lines or waste areas and make sure they are cut down before they go to seed
  • Request that property owners in your area remove noxious weeds (e.g. Canada thistle)