Gardeners everywhere understand how annoying and frustrating perennial weeds can be. For years people have turned to chemicals to solve the problem but as fewer chemicals are now available and more of us want to grow organically could growing a particular plant, Tagetes minuta, be the answer.
Annual weeds maybe the bain of a gardener’s life, especially in spring when the increasing light levels and warm soil mean they appear all over the place. However, a spot of regular hoeing is all that is needed to keep on top of these weeds.
Perennial weeds are another matter. Some, such as daisies and plantain are easily removed but the discovery of some perennial weeds can strike terror into the heart of a gardener. There is a sinking feeling when you come across ground elder, bindweed and, heaven forbid, Japanese knotweed. Most of us would probably turn to glyphosate, a systemic weedkiller, which means it travels through the leaves, into the main body of the plant, where it is transported through to the roots killing the whole plant. Although glyphosate is deemed to be a fairly safe chemical because it is broken down quickly in the soil, there is talk that it may be banned by Europe in the coming years and I think most of us would ultimately prefer not to use any chemicals.
So could this be where Tagetes minuta comes into it’s own. It’s common name, which I love is ‘stinking roger’ because of the smell given off by it’s leaves. A native of South America it is a half hardy annual which can grow up to 2 metres. It certainly isn’t a looker with tiny nondescript flowers but it’s what is going on in the soil that is important. Tagetes minuta exudes chemicals from its roots which repel weeds such as couch grass, bindweed and ground elder. This is a biological phenomenon called allelopathy, when one organism produces one or more chemicals which influence the growth and ultimately the survival of other organisms.
Tagetes’ ability to cleanse the soil was discovered by a bulb grower in Holland in the 1940s. After the bulb harvest and before he planted his next crop he grew some African marigolds (Tagetes erecta) to sell as cut flowers. He started to notice that land where the marigolds had been growing no longer had problems with eelworms, tiny worms that burrow into bulbs and tubers. Over the next couple of years he continued to clear strips and grow these marigolds, curing his soil of ‘root rot’. He told the local agricultural research team who studied the marigolds and produced a report which became known as ‘The Tagetes Effect’. The Henry Doubleday Research Association (HDRA), now known as Garden Organic, then took up the baton and started their own research to see if there were other members of the Tagetes family that could combat problems such as potato cyst eelworm. Their quest led them to South America where the first potatoes had been grown by pre-Inca civilisations. Land was limited with crops being grown on terraces. There wasn’t the space to rotate their crops and yet they had no eelworms in the soil and this was down to Tagetes minuta which had sacred status amongst these early people.
Working with Swansea University the Henry Doubleday Research Association discovered the 5 important compounds in Tagetes minuta and then a member of HDRA grew some in the hope it would also cure a wireworm problem. It didn’t, but it did clear the soil of ground elder. It seems that the same chemical compounds that deter pests in the soil also interfere with the life cycle of some particularly invasive weeds. Sarah Raven has recently used it to clear a bed of ground elder.
A note of caution however, Tagetes minuta itself is actually considered a weed in over 35 countries, including the USA. It is only a problem though if allowed to set seed which is unlikely if grown in Britain because it flowers late, in September/October. It could be used as a green manure, grown in an area with pests or weed problems and then cut down in autumn with the bushy green foliage being added to the compost heap. Chemicals released from the plant when touched can cause dermatitis so it is advised to wear gloves when handling.
Many of us have used members of the Tagetes family as companion plants for tomatoes to repel aphids but it’s fascinating to discover that plants themselves could hold the key for future ways of controlling pests and diseases.
Seed available from Sarah Raven, Chiltern Seeds and Nicky’s Nursery.
Information taken from The Ecologist Vol 2 No. 3 1972
The Green Lady said:
Have never heard of this. What a great tip! Thanks Wellymoman. Isn’t nature just incredible.
Flâneur Gardener said:
I love how science sometimes come up with such simple solutions, sometimes to a different problem than the scientist set out to solve.
Set a weed to catch a weed – amazing. I have a big veg patch – its around 1000 sq m and I’m aiming to be self-sufficient. I looked at it yesterday and was filled with dread at the amount of weeds and clearing I have to do. Last year I was really enthusiastic, out there every day, this year with a new job I’m just wondering how on earth I am going to cope! http://www.thegoodlifefrance.com/cottage-garden-life-in-france-where-do-i-start/
This plant could be the answer to my dreams especially if I use it like you say as gren manure which I was going to start this year as I need to be more scientific even if it is a cottage garden approach. Thanks for sharing this one, Janine
Pauline Mulligan said:
What an amazing solution, must try it here! Isn’t nature wonderful, we can learn such a lot from her.
Thanks for fab post.Great information.Did you comes across any weedkilling plants for mare’s tail on your travels? V.best Naomi
Bridget Foy said:
Japenese Knotweed in the garden is one of my worst fears!!! There is a patch of it about half a mile away which is spreading rapidly. Deadly stuff!! I don’t believe that glyphosate is as harmless as the purveyors as it would lead us to think. Very interesting post.
Isn’t there a chance that it becomes the new Japweed though? It probably can’t set seed here… but if it did it could be another name to put on the list of problem invasive species.
Very interesting, but I think these miracle cures need to be treated with caution, especially as the plant is non native, as you say in your post it’s considered a weed itself in 35 countries. It’s amazing how one plant can eradicate another though.
Have read about this and almost have had finger poised to order a couple of years ago but for some reason didn’t. Have you tested it out WW ?
Hi Anna, Fortunately I haven’t had the need to try it. There was a small patch of ground elder in my garden when I first moved here. I put down a piece of weed membrane after getting as much of it and it’s roots out as possible and then covered the membrane with some soil and a log pile. Five years later it hasn’t reappeared (touching wood as I write this).It is something I would look at trying but would be careful with it, as several have commented no point replacing one problem with another.
If this works, and the Tagetes doesn’t become a nuisance in its own right, there will be many happy gardeners.
The seeds are also on sale at Chiltern Seeds (no affiliation, etc other than they are fairly local to me) and I’ll be giving them a try at Bag End. Thanks for the info.
Well, we are always learning something new, very fascinating. I have used Tagetes in the greenhouse for the aphid problem and yes it does work. As for weeds, I am very strange I enjoy this job. Mind you some of the borders are wide and it is a concern that I may damage the protruding Lilium shoots.
Thanks wellywoman. I have just written a post about a back breaking weekend trying to remove couch grass. Wish I’d read this first! When would be a good time to plant this tagetes?
It’s half hardy so I guess you could sow it in April with the view to planting it out in mid to late May depending when your last frost is likely to be. You could take a look at the Natural Gardener’s website they have a section about all the different tagetes you can grow and how they can help gardeners.
thanks, will take a look. I’ve always grown one variety of tagetes (don’t know which!) for flowers, so will try this too. Don’t suppose you know of any plants that also kill slugs, do you?!
I wish, allotmentmummy, I wish.
We tried this last year. Our first seeds didn’t germinate and the second sowing didn’t come to much either. We were disappointed but I am trying seeds from another source this year.
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