Brochures
Lawn and Yard Weeds
 Most homeowners groan when confronted with the task of removing weeds from their lawns. Although applying herbicides is not difficult, the risks and precautions involved in mixing, using and storing chemicals, especially in yards where children and pets play, are unacceptable to many people. On the other hand, the prospect of spending hours digging out weeds is not an attractive alternative. This brochure describes how to minimize both hand labour and herbicide use by managing the lawn so that the grass controls the weeds. Healthy grass is tough, resilient and able to out-compete most weeds, therefore, the best weed control program is actually a good turf management program.
Mowing Practices
Mowing correctly is the key to weed control in lawns.
- Mow lawns (except for bentgrass turf) to a height of 6-7 cm or about 2 1/2 inches. The
greater leaf area of longer grass makes its roots grow stronger while at the
same time shading fallen weed seeds and preventing them from germinating. For
example, a recent study found that crabgrass and broad-leaved weeds covered 53%
of the area in plots mowed at 3-4 cm height, whereas in plots mowed at 6 cm,
weeds comprised only 8% of the area. People generally do not notice turf weeds
until they invade 5-10% of the area, therefore, increasing the mowing height
alone can maintain weeds at an acceptable level. Longer turf is also more
resistant to fungal diseases and is more drought resistant because it has deeper
roots.
- Mow often with a sharp blade and leave the clippings on the lawn to fertilize the grass.
This does not contribute to thatch accumulation. Although all mowing is
stressful to grass, it is much better to clip a small amount (less than a third
of the length) frequently than to remove a large amount at longer intervals.
Long clippings should not be left on the lawn as they will shade the grass and
increase disease problems.
Fertility
Most of the weeds common to turf, such as dandelions, English daisy, plantain and thistles are
indicators of poor fertility, compacted soil and either droughty or waterlogged
conditions. Correcting poor growing conditions makes conditions unfavourable for
the weeds and strengthens the grass so that it is more competitive.
- To supplement nutrients from the lawn clippings, use slow release fertilizers or
top dress every year or two with well made, fine compost. Do not over fertilize
with soluble nitrogen because this stimulates soft, lush growth, which is more
susceptible to disease, contributes to the build up of thatch and makes more
frequent mowing necessary.
- Make use of the soil testing service provided by some garden centres to check the soil Ph
(a measure of soil acidity). Apply dolomitic lime as needed to maintain the soil
Ph between 6.5 and 7.0. This is necessary to make soil nutrients available to
plants.
Watering
Water turf deeply, but not often. Soak to the root zone (about 6-8 cm deep) and don't water again until the surface 2 cm has dried out. This promotes deep rooting, drought resistant turf. Do not overwater and create waterlogged conditions, which kills grass roots and leaves room for weeds to become established.
Aerating
In compacted or heavy clay soils, it may be necessary to aerate the soil mechanically every year or two. A lawn aerator can be rented for large areas. On small lawns, repeatedly spiking the soil at a slight angle with a garden fork will suffice.
For the best results, after aerating, top dress the turf with sized sand (.25 - 1 mm), which is available from local gravel companies. This is especially recommended for lawns subjected to heavy use to improve drainage and aeration.
Thatching
Thatch is the layer of undecomposed organic material that accumulates at the base of the grass plants. Some thatch is beneficial, shading roots and reducing water loss, but it should be removed if the layer becomes more than a centimetre deep. Grass begins to root in thick thatch rather than the soil and becomes more susceptible to diseases, chinch bugs and drought stress. Thatch management is best left to earthworms (see box) but can be done mechanically with a heavy rake or thatching equipment.
Earthworms: True Lawn Care Professionals
A thriving earthworm population is important for a healthy lawn. Earthworms burrow in the soil, breaking down organic material into rich fertilizer, mixing it deeper into the root zone and aerating the soil. They are important decomposers of the thatch layer and save the homeowner a lot of work by aerating and removing thatch. Earthworm castings rarely show in grass kept over 6-7 cm high, however, if large accumulations make bumps in the lawn they should be periodically raked or scattered over the grass.
Seeding New Lawns
- Have a soil sample tested for pH and fertility. Follow local recommendations for preparing
your soil type for lawn grass, including proper liming, fertilization, and
incorporation of well digested compost or other organic matter into the soil.
- Weed seeds can lie dormant for years until cultivation brings them to the surface,
therefore stimulate as many weed seeds to germinate as possible before planting.
Cultivate and water the soil, wait for 2 weeks to allow weeds to germinate, then
repeat the process. Seed the lawn after the second cultivation, or better yet,
after a third cycle of germination and cultivation.
- Choose an appropriate seed mix for the conditions: soil type, shade or sun, heavy or
light use, etc. You might consider incorporating varieties of perennial ryegrass
or fescues with endophytes 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 is low growing, stays green, resists drought and works to increase the soil
fertility and break up compaction. Under good management, the soil eventually
becomes so favourable for grasses that they will smother the clover.
Grass With Endophytes
Endophytes are fungi that infect some grasses and live symbiotically in the leaves. They benefit the grass by producing toxins that kill and repel insects and confer some disease resistance. Turfgrass varieties with endophytes are generally more vigorous, more tolerant of heat and drought and more competitive than the same varieties without endophyte infections. Several varieties of perennial ryegrass and fescues with high levels of endophyte infections are now available from turf seed suppliers. When buying, check the lot numbers to make sure seed is fresh because the endophytes may die after prolonged storage even though the grass seed itself remains viable. Do not plant endophyte infected grasses where horses or other livestock might reach it as the endophytes are harmful to grazing animals.
Other Controls
Manual Weeding
Well-established rosettes of dandelions, thistles and plantain lie low enough to be missed by the mower and must be removed. The good news, however, is that longer mowing heights and an improved management program will prevent new ones from becoming established. Dig out the entire root using a sharp weeding tool, a process that is much easier in moist soil. If a large weed leaves a gap in the turf, level the disturbed soil and sprinkle grass seed into the bare spot so that the turf fills in before weeds germinate.
Changing Perceptions
Reduce the weeding problem by changing your idea of what is a weed. Many people like the look of English daisies or dandelions and these weeds do attract beneficial insects to the garden. Weeds with deep roots break up compacted soil and bring nutrients to the surface. White Dutch clover, in particular, should not be considered a weed because it is of long-term benefit to turf.
Modifying the Site
Some areas are weedy because grass simply cannot grow well there. Shady areas, especially under large trees that absorb the available water and nutrients could be planted to shade-tolerant groundcovers or covered with bark mulch, gravel, stones or pavers laid over landscaping fabric.
Heavy traffic areas and "short-cut" paths across lawns are often weedy areas of compacted soil. Change the traffic pattern by fencing, planting hedges or using other barriers. If this isn't feasible, consider mulching or paving the pathways or laying turf blocks in the travelled areas. Turf blocks are hollow concrete pavers that allow grass to grow in the centre, while the weight of traffic is supported on the concrete.
Weed Prevention
Reduce the number of weed seeds entering the yard. Watch for flowering weeds along road sides, driveways and fence lines or waste areas and make sure they are cut down before they go to seed. If there is a patch of noxious weeds going to seed in your neighbourhood, the owner can be forced to remove the weeds under the Provincial Weed Control Act (contact local B.C. Ministry of Agriculture, Fisheries and Food staff) or under municipal bylaws. Although the list of noxious species varies between regions and municipalities, Canada thistle occurs on all lists. It must be cut down before the flowers start to bloom or the seed will continue to ripen in the cut heads and scatter on the wind.
1992
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