Feature

Chemical-free weeding

Waging war on weeds needn’t mean reaching for nasty chemicals – as long as you realise that weeds aren't the enemy.

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Weeds are not just the enemy. They may compete with other plants for nutrients, self-seed and sneak through your garden, but they also play an important role as a groundcover to reduce soil erosion, as food and shelter for insect life, and in increasing biodiversity.

But you don’t want too many of them in your garden, as each is capable of producing thousands of seeds.

Weeding is the least popular gardening activity, and it’s the reason there’s a steady increase in the population of prematurely retired gardeners. So, if you’ve been cast out of your garden by the vigorous invaders and you’re on the brink of giving in, here are a few tried and true organic ways to reclaim your space.

– Household vinegar is five per cent acetic acid, which will burn foliage when sprayed on plants. Acetic acid breaks down in water, so spray on a sunny day. As household vinegar is two to three times lower in acetic acid than the industrial strength variety, you may need to reapply periodically to achieve good results. This works well over small areas, but it’s not a cheap option for large gardens.

– Hand weeding is best done on the micro scale; let them get too big and they’ll have entwined their root systems with those of valuable plants and generally out-competed them for nutrients. A small amount of time
spent often is better than letting it go for months and then wrestling with weed monsters all weekend. The weeds will come out more easily when the soil is moist.

– Mulching the soil creates a dense layer that excludes light and stunts weeds. In exceptionally weedy areas, lay it on thick – at least 15 cm deep – otherwise weeds will grow through. Mulch on wet ground as it will help retain moisture. Choose sugar cane mulch or weed-free straws where the heads have been harvested, or you may end up with even more weeds. Weed mat can be used successfully over small areas.

– Pouring boiling water on weeds is a good technique for paths. It’s not very energy efficient to use this technique over a large area, but you could knock out one or two with, say, the water you’ve just boiled your eggs in.

– Growing a green manure crop over bare vegie patches in winter will ward off weeds. Just make sure you slash it before it has a chance to set seed. This green coverage will protect the soil from erosion, increase humus levels and soil health, retain moisture and out-compete the weeds at the same time.

– Taking the zero-tilling approach can reduce weeds, as any weed seeds brought within 10 cm of the soil surface are likely to sprout. Adding additional humus to the soil surface will benefit soil structure and encourage worms, those tireless tunnellers who till your soil and add nutrients for free.

– Chooks like their greens, and they’re not fussy what kind. A few weeks of intensive chook ‘grazing’ and you’ll have exchanged weeds for nitrogen-rich fertiliser and a few eggs. Once the chooks have done their work, mulch the soil heavily to preserve the additional nutrients and stop the plants’ recovery.

– Changing soil conditions can help. Some weeds thrive in acid or alkaline soils only – you can change the soil environment and reduce their health if you can find out what soil types they thrive in. Lime and animal manures increase alkalinity; sulphur, used in small amounts, increases acidity. Most Australian soils are acid. Check yours with a soil pH kit before amending.

Composting weeds

You can turn weeds into liquid compost, as many are high in various trace elements. Cobbler’s peg, for instance, is high in iron. Put the pulled weeds into a bag along with a few kilograms of chook manure. Tie it closed and suspend it in a lidded bucket of water for several months. Dilute the ‘weed stew’ to the colour of tea and pour it
on plants for a foliar feed.

I once made the mistake of pulling up hundreds of seeding weeds and throwing them in the portable chook tractor, thinking the chooks would take care of the rest – which they appeared to be doing. However, the weed seeds passed unharmed through their digestive tracts, mixing in with a nice bit of chook fertiliser. Within a month I had a hundred times as many weeds. What I should have done was hot compost the lot. Hot composting raises the temperature above 60°C inside the heap, killing most seeds, and eventually the compost can be returned to the garden without fear of further weed outbreaks.

A pile of assorted materials at least a metre high and wide is needed for hot composting. Good ingredients are sawdust, seaweed, weeds, lawn clippings, leaves, animal manure (of non-meat eating animals), shredded paper and kitchen waste (minus any meat products, onions and citrus peel). Mix them well, moisten the heap and it will soon start to decay. Expect to see steam rising from the pile within several days. Turn the pile over periodically to aerate it for best results.

Weeds are a war that can never be won. A windy day is all that’s required for a migration of weed seeds to your garden.

The wise response is to recognise that weeds are only plants we haven’t yet found a use for.