Mexican marigolds as weedkiller


Hello, I am looking to plant something right on or next to my property line to prevent my neighbours’ weeds migrating over and under our fence. The neighbour property is over run with weeds and does not take care of his garden. A few years ago, I installed a plastic upright barrier under the fence. This hasn’t been successful as it has moved in time and left gaps. I read about the Mexican Marigolds (targeted minuta) as a possible solution. It’s suppose to destroy noxious weeds. My concern is that I’ grow roses and a variety of perennials in the same bed. Will this plant negatively affect the wanted plants in my garden. Are there other alternative plants suited for the same purpose in no man’s land. Thank you.


Thank you for contacting Toronto Master Gardeners.

Mexican marigold, botanical name Tagetes minuta, is a strongly scented, sun-loving annual plant that can grow to 50-150 cm. It has small white flowers.

Root secretions of Tagetes minuta have a herbicidal effect, inhibiting the growth of certain plants growing nearby. It has been found to be effective against perennial weeds such as Ranunculus ficaria (celandine), Aegopodium podagraria (ground elder), Glechoma hederacea (ground ivy), Agropyron repens (couch grass).

It could harm plants that you want to grow.

The root secretions also have nematocidal and insecticidal properties, so not just the weeds, but potentially useful animals and insects could be inhibited by the root secretions. The essential oils from this plant have also been shown to be bactericidal, so the Mexican marigold could harm beneficial soil bacteria too.

I think your best option is to install a metal barrier (not wood or plastic which will degrade) in the soil at the fenceline. Another Master Gardener has used grey rolled sheet aluminum for a barrier against goutweed from her neighbours. She dug down about 12 inches (30 cm) as close to the fence as possible, inserted the metal barrier and filled the trench with new, non-weedy soil. The barrier should extend 5-7 cm above ground level so you can see it and not kneel on it. The barrier must extend far enough at each end of the fence to avoid weeds spreading around the end of the barrier. Discard any weed infested soil you remove in heavy black plastic bags and put out for garbage, not yard waste.

Good luck with controlling the unwanted weeds in your yard.