Lawn Weed Control in Ontario: What's Legal Under the Pesticide Ban
Ontario bans the cosmetic use of pesticides on lawns, so products such as 2,4-D and glyphosate cannot be used to kill weeds in a typical residential yard. You can still use products whose active ingredients are all on the province's Allowable List, such as corn gluten meal, soap or acetic acid, and iron-based herbicides are widely used by Ontario lawn care professionals. The most reliable weed control, though, is a thick, healthy lawn: mow high, fertilize in spring and fall, aerate and overseed thin spots.
Fall is a good time to act. Perennial weeds like dandelions are storing energy in their roots, and grass is recovering from summer. Here is what London-area homeowners need to know.
What the Cosmetic Pesticide Ban Covers
Under Ontario's Pesticides Act and its regulation, using a pesticide for cosmetic purposes is prohibited unless an exception applies or every active ingredient in the product is on the province's Allowable List. The current version (Version 5) took effect on November 28, 2022. You may still see older references to "Class 11" pesticides; that classification was replaced by the Allowable List in 2020.
The province's guide to pesticides for home lawns and gardens names 2,4-D, glyphosate and diazinon as examples of ingredients that are banned for cosmetic use on lawns, gardens, patios and driveways.
Exceptions
The ban has exceptions, including:
Golf courses, under conditions
Agriculture and forestry
Public health or safety, including plants poisonous to the touch such as poison ivy, and invasive giant hogweed
Specialty turf, cemeteries and sports fields used for national or international events
Natural resource management
A weedy front lawn is not one of them.
What about London's own by-law?
When the province brought in the ban in 2008, the Pesticides Act was amended so that municipal by-laws addressing the cosmetic use of pesticides are inoperative. In other words, the provincial rules apply in London and across Ontario, rather than a patchwork of local by-laws.
Weed Control Products You Can Still Use
Products are only allowed if every active ingredient is on the Allowable List. Examples named by the province and by York Region include:
Corn gluten meal, which is used as a pre-emergent on lawns
Soap-based products
Acetic acid (vinegar-based) herbicides, which burn foliage and are non-selective
Borax and sulphur
Mineral oil
Iron-based herbicides
Iron-based herbicides, sold with the active ingredient FeHEDTA, have become the go-to selective broadleaf product for Ontario lawn care professionals. In a 2010 trial by an Ontario Ministry of Agriculture turf specialist, an iron product applied in October controlled dandelion and black medick, with a second application about four weeks later sometimes needed.
University extension research describes how these products work. Treated weeds blacken within hours. They work best on small, actively growing weeds in cool spring or fall weather, and repeat applications are often needed. Grass may darken briefly after treatment. A study by the Guelph Turfgrass Institute reached about 95% weed-free turf after three applications.
Before you buy anything, read the label and check that it is permitted for lawn use in Ontario.
Why Fall Is Prime Time for Weed Control
Late September through October is a valuable window in southwestern Ontario:
Weeds are pulling energy down into their roots, so treatments that damage the leaves have more effect.
Cool weather suits iron-based products, which work best on actively growing weeds in cool conditions.
Grass is recovering from summer heat and can fill gaps before winter.
Overseeding in late fall helps thicken the turf, and thick turf leaves less room for weeds in spring.
If your lawn is thin, our guide to dormant seeding in Ontario explains how to seed late in the season so the seed sprouts in spring.
Cultural Controls: The Habits That Crowd Out Weeds
The province's guide to managing pests naturally recommends habits that build a dense, competitive lawn:
Mow high. Keep grass 2 to 3 inches tall with a sharp blade. Taller grass shades the soil and makes it harder for weed seeds to sprout. Never cut off more than one-third of the blade at once.
Water deeply, not often. About 1 inch per week, generally in one watering early in the morning, encourages deep roots.
Fertilize in spring and fall. Natural or slow-release fertilizers feed the grass so it can outcompete weeds.
Aerate. Core aeration in spring or fall relieves compaction, which is common on London's heavier soils.
Topdress and overseed. Spreading a thin layer of quality soil and overseeding in early spring and late fall fills thin areas.
Fix the soil. Low spots, compacted clay and poor topsoil all favour weeds. Adding screened topsoil where the soil is thin gives grass a better start.
Common Ontario Lawn Weeds and What to Do
Dandelions: Dig out young plants, including the taproot, or spot-treat with an allowed product in fall. Thicken the turf so seedlings cannot establish.
Clover: Clover often signals low nitrogen. Regular fertilizing helps grass compete. Many homeowners now leave some clover, because it stays green and feeds pollinators.
Black medick: Thrives in thin, dry, compacted lawns. Aerate, fertilize and overseed; iron products have shown control in fall trials.
Crabgrass: An annual that fills bare spots in hot weather. The best defence is dense turf and mowing high. Corn gluten meal is used as a pre-emergent in spring.
Creeping Charlie (ground ivy): Loves shade and damp soil. Improve drainage and sunlight where possible and consider shade-tolerant grass.
Weed Control Checklist for Fall
Mow at 2 to 3 inches until the grass stops growing.
Hand-pull or dig larger weeds while the soil is moist.
Spot-treat broadleaf weeds with a permitted product, following the label.
Aerate compacted areas.
Overseed thin areas, or plan for dormant seeding.
Apply a fall fertilizer.
Check for grub damage, which leaves thin patches that weeds invade; see our article on fall grub damage in Ontario lawns.
Rake or mulch leaves so they do not smother the lawn over winter.
When Weeds Mean It's Time for New Sod
If more than half of a lawn is weeds, bare patches or moss, it may be faster to start over. Stripping the old turf, correcting the grade, adding good topsoil and laying fresh sod gives you a dense lawn right away. Our comparison of sod vs. seed in southwestern Ontario can help you decide which route fits your budget and timeline.
FAQ
Can I use 2,4-D or Killex on my lawn in Ontario?
No. Ontario bans the cosmetic use of pesticides, and the province names 2,4-D as one of the ingredients that cannot be used to control weeds on residential lawns.
What weed killers are legal in Ontario?
Products whose active ingredients are all on Ontario's Allowable List can be used. Examples include corn gluten meal, soap, acetic acid, borax and sulphur. Iron-based herbicides (FeHEDTA) are widely used by Ontario lawn care professionals. Always check the label.
Is fall a good time to treat lawn weeds?
Yes. Cool weather suits iron-based products, perennial weeds are storing energy in their roots, and a 2010 Ontario trial found an October iron treatment controlled dandelion and black medick.
How high should I mow to prevent weeds?
Ontario's guidance is to mow at 2 to 3 inches with a sharp blade. Never remove more than one-third of the blade at a time.
Does London have its own pesticide by-law?
The provincial ban applies across Ontario. The Pesticides Act makes municipal by-laws that address the cosmetic use of pesticides inoperative.
Is a weedy lawn worth saving?
If weeds are scattered, overseeding, fertilizing and mowing high can turn it around. If more than half the lawn is weeds or bare soil, new sod on improved topsoil is often faster.
Get a Thicker Lawn Next Spring
SPM Landscape & Excavation has installed sod and repaired lawns across London since 2006. We are WSIB covered with $1 million in liability insurance. Call (519) 474-0008 or email spmlandscape@gmail.com for a free quote.
Comments