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!