How to Control Weeds Without Commercial Weedkillers
After you've softwashed a Cobblelock or block paving drive or patio it's going to look great. And your customer is going to be very happy indeed.
But then ... weeds can return all too quickly, spoiling your work.
So what to do?
Applying commercial herbicides (aka chemical weedkillers) requires the person applying them to be trained and licensed in their application, which is a good move for any softwash contractor to consider. But what do you do before getting licensed, or if you just don't want to pour Monsanto's best into our good earth?
Btw: The environmental impact of weedkiller chemicals such as Monsantos's notorious glyphosate (aka Roundup) remain extremely questionable. Many people do not like to use them because of their probable negative impact on the food chain.
So how can you and your customers keep on top of weeds while caring for the environment?
One answer is to treat weeds with common table or cooking salt, available in bags from any supermarket. But note ... Salt is a powerful weedkiller and must be treated with great respect.
Is salt a pesticide?
No. But as some people have expressed concern about this we sourced these dictionary definitions of a pesticide: "A substance used for destroying insects or other organisms harmful to cultivated plants or to animals."
And "A chemical or biological substance designed to kill or retard the growth of pests that damage or interfere with the growth of crops, shrubs, tress, timber and other vegetation desired by humans."
Neither of which sound like the substance we put on our fish and chips. A pesticide is a substance designed to kill pests that are harmful to plant life that we want to keep.
- As salt is not a pesticide or biocide there are no regulations governing it's use for weed control.
A test of salt to control weeds alongside a footpath
Important: Note the width of grass-kill in the photos. Although we spread salt only 7-10 cm from the path, the salt has leached and killed the grass to a depth of 15 cm.
The photographs show the dramatic effect of sprinkling pure salt onto grass, after only 14 days.
So be careful when applying salt to your customer's drives and paths. Be aware of the possible leaching of salt into nearby plant borders. Used in small quantities (approximately 10% salt to 90% sand) in the cracks between paving slabs on paths and drives it should be fine. But we are not suggesting the wholesale use of salt in large quantities, or the spreading of salt directly onto concrete.
Salt has leached into the grass twice as far as it was applied. We sprinkled the salt by hand onto the grass (the photos do not show leaching from the concrete paving) to show an exaggerated effect simply to emphasise how powerful salt can be as a weedkiller.
The same path showing a corner where leaching is even worse. Probably because rain water builds up in this area, carrying the salt further into the lawn.
Important: To minimise any negative effects from leaching it's a good idea to only apply the salted sand mix to a minimum of 5 cm from the edge of the paving. Fill in the last 5 cm with un-salted sand. Any salt that leaches from the salt/sand mix will be absorbed by the un-salted sand before it reaches your customer's plant life.
Salt is a "residual" weed control method
This means the salt stays in the ground for a long time – months and even years – which is obviously not great for growing flowers, veg and lawns.
However, we can use this residual effect of salt to our advantage in discouraging weeds from growing in the cracks in Cobblelock and other paving.
We do not recommend sprinkling salt directly onto concrete surfaces as it can damage the concrete. We suggest using only a 10% salt to 90% sand mix to fill the cracks between paving. Ensure you leave the surface of the slabs or bricks brushed clean of all salt mix before you leave.
Do not even think about brushing or washing surplus salt, or salt/sand mix, onto areas where your customer is growing trees, lawns, veg, or flowers. Just brush it up and remove from the site, or place into other cracks and crevices in the path.
- Keep salt away from ponds and other aquatic environments. DO NOT APPLY if there is ANY danger of salt leaching into a fresh water aquatic environment.
How can your customers control the weeds after you are gone?
Using salt to control weeds by mixing it into the sand between paving slabs or bricks will help keep your customer's paths and drives clear of weeds for several months. But no weed-control treatment is permanent, so here are some ideas you can offer your customer who does not want to use commercial chemical weedkillers:
- Add washing up liquid (Fairy Liquid is the best) and vinegar to a salt water solution. The vinegar reduces the surface tension of the fluid and helps it be absorbed by the leaves of weeds. The soap helps the solution stick to the leaves of the weeds. Simply apply using a household hand-held pump sprayer directly to the leaf surface of the weeds (and be sure to wear eye protection and fully rinse the sprayer, chemical-resistant gloves and skin after use).
- Add salt and vinegar (or cider vinegar) to boiling water and pour or spray directly onto weeds. This can be a highly effective way to kill weeds on paths, drives and patios.
Note: the vinegar for sale in supermarkets is only 5% acetic acid, which will work to some extent but is unlikely to kill the weeds to their roots. If you want a really powerful vinegar weedkiller use horticultural vinegar at 10-80% acetic acid. Note that, because horticultural vinegar contains 10–80% acetic acid, it may be described on the label as "acetic acid" rather than vinegar. Dilute it 3-10:1 before use.
Take great care when applying horticultural vinegar, covering your skin and wearing protective chemical-resistance gloves and goggles as at that concentration vinegar is a powerful and potentially dangerous chemical. A weedkiller based on horticultural vinegar will effective in killing weeds but will also harmful to humans. A concentration as low as 11% acetic acid can burn skin and eyes.
- Pour boiling water alone with or without vinegar – but without salt – onto individual weeds. This is also highly effective but does not have the residual effects of salt. It will kill off the surface of weeds but will not kill them to the roots, so they tend to quickly regrow.
Important: Tell your customer to take great care when spraying weeds as "spray drift" onto adjacent plants can be lethal to adjacent plant life. Keep the spray nozzle very close to the weeds they want to treat, protect any plants that may be exposed to spray drift, and apply on a windless day.
We do NOT recommend using salt or vinegar solutions for controlling weeds on soil that is, or is going to be, used for growing lawns, veg or flowers as the salt will remain in the ground for a considerable time. Used cautiously and sparingly with respect for our environment however, it can be a boon that helps keep paths, drives and patios clean and tidy.
- If your customer wants to use a chemical weedkiller (aka "herbicide") to control weeds on their property we suggest you simply point them to the nearest garden centre – online or offline – and let them apply the chemicals according to the product labelling instructions.
Unless you are legally certified to work with pesticides and herbicides, we suggest you do not offer advice or information to your customer on their use.
Click here to learn about getting trained and licensed in the application of pesticides and herbicides
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