Lawn Care Program: Weed Management

Weed management is a process of eliminating weeds in your lawn through a combination of weed control methods, awareness of growing conditions, and building a healthy, thick lawn. To get rid of weeds you need to care for and manage your lawn correctly.

Weed seeds are always present in the soil and lawn waiting for the opportunity to grow. Weeds are opportunistic. Weeds are either annuals or perennials. Annual weeds die at the end of the season and can leave bare spots in your lawn providing the opportunity for other weeds to take root in the spring. Examples of annual weeds are knotweed, oxalis, purslane and spurge.

dandelion managementDandelions can be annual or perennial. Perennial weeds re-grow from their roots annually and can spread on their own taking advantage of weak grass and bare spots. Perennial weeds include dandelions, plantain, creeping charlie and thistle. Even if you kill these weeds from the top they will still spread from their roots.

Being aware of growing conditions that weeds prefer is important in their management and control. Knotweed is an indicator of soil compaction and a hot growing environment. By changing the growing conditions knotweed can be managed by relieving compaction (thru core aeration, less foot-traffic and topdressing) and cooling the growing medium (with regular watering).

getting rid of knotweedSoil pH has a profound effect on growth of your lawn as well as their weeds. A soil test for pH should be done annually to give scientifically sound direction for your site specific lawn care program. There will be less dandelions in soils with a pH of 4.8 than in soils with a pH of 6.4. And dandelions will thrive at a pH level of 7.5.

Crabgrass grows in either acidic or alkaline soils. Crabgrass grows best in poor quality soils, lawns cut too short, lawns with disease and/or insect damage and in high traffic areas. Violets and ground ivy like soils that are slightly acidic. Normal soil pH is 6.5 to 7.0 which is slightly acidic. If lawn soil is too acidic then add dolomitic lime. If lawn soil is too alkaline then add elemental sulfur.

Weed management would include ensuring growing conditions of specific problematic weeds are addressed. Weed management and control includes hand pulling and removal of annual as well as perennial weeds and ensuring that any bare spots are filled with grass seeds via over-seeding and re-seeding.

Mowing the tops off of weeds prior to going to seed will help control weed infestations also. Harmony Gardens Landscaping Inc. recommends the use of Turf-Maize corn gluten herbicide to prevent weed seed germination.

turf maizeTurf-Maize is effective at preventing germination of seeds for up to six weeks time. Be aware that it prevents germination of grass seed as well as weed seeds and so timing of applications is vital to ensure building of a healthy lawn. Turf-Maize is highly effective at preventing weed seed germination and thus weed infestations thru new weed growth. Turf-Maize does not kill off existing weeds.

With the pesticide and chemical herbicide ban effective in Ontario the killing off of weeds is now more complicated. There are “organic” herbicide products such as Fiesta also called Weed B Gone and horticultural vinegar available to address specific control of weeds.

Success of these organic herbicides depends on many factors such as timing, temperature, application rates and targeted weeds. “Softer” types of weeds such as dandelions, thistle and white clover can be effectively controlled with an application or two of Fiesta or horticultural vinegar whereas woodier rooted weeds such as oxalis, creeping Charlie and knotweed see no reduction from applications of Fiesta.

The third aspect of weed management is to build a healthy, thick lawn that is resistant to weed growth and prevents weeds taking hold by not providing them the opportunity. To build a healthy, thick lawn one must have a lawn care program based on soil test results and good maintenance practices.

dethatching lawnA healthy lawn will need to be maintained by de-thatching to remove thatch, core aeration, proper fertilization, top dressing, over-seeding, weekly mowing at a height of 2.5 to 3”, watering lawns 1” per week, and supporting normal dormancy periods to decrease lawn stress. A thick lawn is your greatest defense against weeds.

Healthy lawns are effective in weed control as well as pest/disease control. For specific lawn maintenance practices please refer to other articles in our “Ask an Expert” »

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