War on weeds

Sunday, 28 May 2017

Use of wood chips as a mulch; nature strip in Cheltenham, Sydney

This past week a scandal has erupted in the horticultural world, with the news that chemical giant Monsanto has been for years covering up research findings that show that its weed killer glysophate (found in Round Up and Zero) is a probable human carcinogen. This has wide implications, especially since Monsanto developed genetically engineered food crops that were immune to glysophate so that they could be sprayed with the chemical to kill weeds. Who amongst us hasn't used this product at some time or another, having been assured by the company that it is totally safe! I've been avoiding it for some time now, since I started hearing whispers about its dangerous side effects over the past year, and now more than ever do I think we home gardeners need to find alternative, environmentally safe methods of weed control.

Good old hand weeding has a lot going for it - I am always dismayed when I see people spraying weeds they could have simply bent over and tweaked out in a moment. There is something quite meditative about weeding, and it gets you up close and personal to your plants so you can really see how they are going. Sometimes you find interesting an interesting self-sown seedling amongst the weeds, which can be nurtured, potted up or moved to a better spot in the garden. If you hadn'tt been weeding, you might never have seen that seedling!

I usually put my weeds into our council green bin (though when we had chooks, they used to eat a lot of my weeds), but some people like to put them in an old plastic garbage bin and top it up with water, thus drowning the weeds. After a month or so, the resultant 'weed tea' can be used as a liquid feed for the garden, returning the nutrients that the weeds stole from your plants in the first place - or the whole lot can be put in the compost heap to break down and be used later as a mulch or a soil conditioner.

Leucothoe fontanesiana in my garden, surrounded by fallen crepe myrtle leaves

Once an area is weeded, it makes sense to apply some sort of a mulch to the surface to discourage further weeds from germinating. I've been using cane mulch for a few years, which works well, but this year I am spreading small autumn leaves on some borders as a mulch, and shredded larger autumn leaves on other beds; and I quite like the look of these mulches. Half-decomposed compost is another good material to use. As all these mulches break down, they will nourish plants and improve the structure and water-holding capacity of the soil. Make sure all mulches are kept away from the stems of plants, as this can be harmful by causing them to rot off. For areas comprised mainly of shrubs and trees, and where there is little time for weeding, a thick layer of wood chips can work well, as shown at the start of the blog. This method is useful for nature strips, for example.

Groundcovers growing close together in my garden to try to stop weeds invading

Growing groundcover plants so that they merge together to form a weed-suppressing carpet is another way to reduce weeds - by not giving them a place to flourish! It's important that the area is as weed-free as possible when the plants are put in, and mulched until they start to join up. Weeds love empty spaces, so minimising these is one way to reduce the weed population in your garden.

For very difficult areas that are choked with weeds that you'd ultimately like to develop as a garden bed, it is possible to use sandwich mulching, putting thick layers of newspaper over the soil and covering this with a 10cm layer of mulch such as cane mulch or lucerne. The weeds will eventually (we hope) starve to death! Some gardeners also put layers of newspapers or cardboard under their mulch throughout the garden, though I have never done this. I've also heard of solarisation methods, where the weed-ridden area is covered for a few weeks or so with a large piece of thick, black plastic and held down with stones or bricks. This apparently cooks and kills the weeds.

Paving weeds in my garden to be treated with boiling water

In paving, I have quite good success pouring boiling water over weeds. It is quite satisfying to see them shrivel in front of your eyes: the effect is delightfully instant! I've managed to keep my paths fairly weed-free by this method by boiling up a kettle of water every week and pouring it on anything that has popped up. The heat bursts the cells as the leaf expands under the impact of the boiling water, destroying the cellular structure of the plant. In some cases, if the weed has a strong root system, it may eventually re-grow, but the same thing happens when using herbicides!

Onion weed in my lawn

Of course, some weeds are notoriously difficult to dig out effectively - onion weed, soursob and oxalis spring to mind! I have heard that dribbling machine oil onto the middle of an onion weed plant can smother the bulb, but I have yet to try this. Another general point to make about pernicious weeds is to be careful with what you plant in your garden in the first place: I despair when I see plants such as toad lily (Tricyrtis), bog sage (Salvia uliginosa) and snow poppy (Eomecon) for sale in nurseries, as in my experience (yes, I have planted them all in my time) they are almost impossible to get rid of!

In recent times, organic herbicides have come onto the market, some based on pine oil, others combining vinegar and salt. It is apparently possible to make your own version of the latter by combining a cup of table salt with a litre of white vinegar. I have not tried this yet! I am currently just starting to experiment with a product called Slasher, from Organic Crop Protectants, which uses pelargonic acid to kill weeds. Pelargonic acid is a substance that is found naturally in the oil of pelargonium plants. The product is said to be non-residual and harmless to people and the environment (apart from the weed, of course!). The whole of the weed needs to be covered with the spray as it works by contact only. I am hoping this might be the answer to weeds that cannot be overcome in any other way. Please let me know any other ideas you have for us to battle weeds without recourse to horrid dangerous chemicals!

I will be having a short break from blogging - I will be back soon!

My previous blogs at this time of year:
2010
30 May
2011
22 May
2014
25 May
2015
31 May

Reader Comments

  • By Carole - 2264 (Zone:10 - Warm Temperate) Monday, 29 May 2017

    ....thanks so much Deirdre for your alert re Monsanto"s weed-killers. Trust they will be dealt with for their cover up - bad guys! For pathways, like you, whenever I boil the jug most days - I take the excess out to the paved paths, then come back in and enjoy my cuppa break :). Why do I feel though as I pour away --- hoping there"s not a worm or two under there ......... Aargh, I never thought about worms beneath my pavers! Deirdre

  • By Kerrie - 2104 (Zone:10 - Warm Temperate) Monday, 29 May 2017

    Oh my gosh this is the first i have heard of this news re Monsanto & Roundup. I"ve lived in some challenging gardening areas in my time where professionals wanted to use Roundup & I"ve always been reluctant going back 15 to 20 years even as I"ve always had cats & used to express my concern about their welfare walking & lounging in sprayed areas. They"d always scoff & say it"s perfectly safe for pets until i made the comment, " would you allow your baby or toddler to crawl around on it?" I never liked my cat walking around either in the garden after we had applied Roundup. Deirdre

  • By Kerrie - 2104 (Zone:10 - Warm Temperate) Monday, 29 May 2017

    There response would always be a bit of a shocked looked & a "no" response to which I"d reply, "well don"t tell me it"s safe for pets then" When it had be used I"d keep the cats & dog inside for a couple of days at least & then hose down if possible. Would love to hear more of your experiences & recommendations re natural weed killers. I"ve been using a clove oil based one with mixed results. I will report back when I have seen how the pelargonic acid one goes! Deirdre

  • By Sue t. - 2566 (Zone:10 - Warm Temperate) Monday, 29 May 2017

    My cats and I don"t use Round Up either. I found that the couch grass in my paving was too tough for boiling water and commercial vinegar based weed killers so I covered the lot with black plastic sometime last year. One day I"ll look underneath and hopefully the couch will be gone. Nothing matches the joy of digging out an oxalis clump with all its bulbs but you do have to get every little bulb. Hope that black plastic method works. I do dig up a lot of oxalis and I think over the years it has got less! But still pops up here and there. Deirdre

  • By Bren - 2540 (Zone:10 - Warm Temperate) Monday, 29 May 2017

    I have every weed in the calalog in my garden. I have used the newspaper and mulch method extensively; it works well, but even then some weeds such as oxalis and Montbrecia (Watsonia?)are difficult to prevent. Certain plectranthus species simply drown out weeds,but I am looking for an effective groundcover to drown out wandering jew. Now seems to be the time to get rid of onion weed; once spring arrives the bulbs will multiply. Now it is one bulb per plant. I patrol daily! That sounds a good strategy. I use the silver stripey wandering jew cousin to conquer the green version - sort of works - see the picture of the groundcovers in the blog! Deirdre

  • By Mary - 2089 (Zone:10 - Warm Temperate) Monday, 29 May 2017

    I agree with you that depriving weeds of room and light is the best way to go; also to be aware of the invasiveness of plants we bring into the garden. I had not heard about the latest scandal but I remember being told that salesmen used to demonstrate the safety of the herbicide by drinking it. Gosh, one wonders what happened to those salesmen! Deirdre

  • By Lloyd - 4060 (Zone:11A - Sub-tropical) Monday, 29 May 2017

    Can anyone confirm please: bindii is making its annual appearance in Brisbane at the moment - not flowering just yet. Can this be killed by simply cutting the plant off at ground level, separating the green growth from the roots. It would be much faster than digging it out. Similarly, can winter grass be dealt with the same way?

  • By David - 2068 (Zone:10 - Warm Temperate) Monday, 29 May 2017

    Unfortunately there is quite a bit of glyphosate residue in foods. Much of this is due to the practice of "crop dessication" where a whole grain crop is deliberately sprayed just before harvest to dry it off nice and evenly. The public is mostly unaware of this. See https://en.wikipedia.org/wiki/Crop_desiccation For Maximum Residue Limits (MRLs) specified by FAO see http://www.fao.org/fao-who-codexalimentarius/standards/pestres/search/en/ (type "glyphosate" in the search box). Really scary stuff; thanks for letting us know about this. Deirdre

  • By Kerrie - 2104 (Zone:10 - Warm Temperate) Tuesday, 30 May 2017

    I use Enviroclean Fruit & Veg wash to wash all myfruit & veggies befire eating to remove any chemicals left on them. Horrifies me to see parents letting their kids eat unwashed fruit while they are shopping, especially blueberries which are heavily sprayed. Yes it is a worry to think what has been sprayed on our food. Deirdre

  • By Margaret - 2122 (Zone:10 - Warm Temperate) Wednesday, 31 May 2017

    It is horrifying that the chemical companies are so untruthful about their products. I use non-chemical products on my weeds - salt and vinegar work well, as does hand weeding. Replying to Lloyd, I have found that only weeding out both bindii and winter grass works, but, because they are prolific seeders, and some will be missed in the weeding process, both will return, annually. It is a long process, but with persistence, they will disappear, in my experience.

  • By Helen - 7256 (Zone:10 - Mediteranean) Wednesday, 31 May 2017

    Agree wholeheartedly that its best to avoid herbicides. Full hazards of them probably not yet known. Mechanical removal, Mulch & solarisataion work very well for me. BUt some weeds very stubborn & require repeated digging out of every scrap + mulch & continual follow up. eg Acanthus mollis (bears breeches), oxalis, arum lily. Yes, perseverance is required to conquer many weeds! Deirdre

  • By Helen - 7256 (Zone:10 - Mediteranean) Wednesday, 31 May 2017

    RE SALT ---it does kill weeds, but also damages the soil. You may get away with it in the short term. BUT It is washed into non target areas and repeated use over time will kill everything--plants, soil microorganisms, insects, worms --the lot. This is why salt is often used as a preservative or antiseptic. I cannot believe it is promoted as a weed killer. It may be a common household product but this doesnt make it appropriate for garden use. You have made a very good point, Helen; it does seem madness to use salt in the long term. Deirdre

  • By Richard - 2066 (Zone:10 - Warm Temperate) Wednesday, 31 May 2017

    I too have heard about a lot of worries regarding Glysophate and its role as a carcinogen and even suggested to my gardening service that we replace it with Slasher as a precaution. However, subsequently I found a report (just put Glysophate in your web browser and it is the fifth or sixth item to come up) by the Australian Pesticides & Veternary Medicines Authority that concludes Glyphosate poses no risk to humans if used according to instructions on the label. Richard I suspect that the authority you mention is probably basing its advice on what Monsanto has been saying all these years, rather than any independent research? But I could be wrong. Deirdre

  • By Noeline - 2081 (Zone:10 - Warm Temperate) Friday, 02 June 2017

    When you see what glysophate does to living plants I shudder to think what it does to human cells I have found mulching my shrub garden with bark and veg with sugar cane and under the trees I pile up the autumn leaves seems to keep the weeds to a manageable level.Salt leeches into the surrounding soil and poisons it. I agree Deidre ground covers are a great answer it just takes time to establish the nice ones:) Thanks, Noelene. I do find mulch very helpful and am busily putting autumn leaves on my garden beds at the moment! Deirdre

  • By Barb - 4358 (Zone:10 - Warm Temperate) Friday, 02 June 2017

    Interesting to read everyone"s comments- I burn my bindi patches - works a treat - I use a little gas blow torch that you can refill - think it is used in the kitchen to brown creme brle :) burning kills the plant and the seeds. My Dutch hoe is my favourite tool for weeding the vege garden - kills the weeds and lets in air into the soil - a few minutes weeding is never wasted time in the garden - Happy weeding everyone ! I love that suggestion about the mini gas blow torch! We have one of those in the kitchen and I must try using it like you do. Deirdre

  • By Richard - 2066 (Zone:10 - Warm Temperate) Friday, 02 June 2017

    Deirdre - I hear a note of scepticism which can often be well-founded. However, the initial assessment was made by the World Health Organisation International Agency for Research on Cancer.Now the WHO pesticides experts are doing a comprehensive risk assessment of Glysophate and look at all scientific studies including unpublished scientific data which will be peer-reviewed during the assessment process. Sounds like rather more then the APVMA reprinting a Monsanto press release I reckon. It does sound as if it will be a worthwhile review and I will be interested in seeing their conclusions. Deirdre

  • By Meryl - 2206 (Zone:10 - Warm Temperate) Monday, 10 July 2017

    Thanks, Richard.

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