DIY Natural Weed Killer

Last time we shared this weed killer recipe we had a few emails from customers who were concerned that the salt leftover from the soda ash in the soil would make it difficult to plant into. That’s not the case, making your weed killer from soda ash and water will only temporarily raise the PH of the soil.

 A good amount of rain or some generous irrigation and the soil pH should return to a normal level. If you apply this weed killer topically it will adhere to the plants that you want to exterminate due to the dish wash liquid in the recipe. For the best results apply on a warm dry day so that the sun can help activate the soda ash for maximum effect.

In any case it’s vastly better than applying toxic Roundup to your weeds and garden!

Here’s some technical talk about this weed killer from NZ’s gardening guru Dale Harvey …

“Soda Ash (Sodium Carbonate) =Na2CO3 which breaks down naturally into Na2O (Sodium Oxide) = a salt and CO3 (an unstable compound) that quickly becomes CO2 (Carbon Dioxide) and O (Oxygen).

When mixed with water the chemistry becomes Na2CO3 + H2O = 2NaOH + CO2 or Sodium Hydroxide plus Carbon Dioxide.

Sodium Hydroxide is a strong alkaline base salt that can raise soil pH to as high a 9.8, pH 7 is neutral and most plants will not tolerate a pH higher than 9.0-10.0 thus making your weed killer from soda ash and water will salt the land and raise the soil pH at least temporarily enough to eliminate most weeds and noxious roots”

DIY Natural Weed Killer
500g Wendyl’s Green Goddess Premium Soda Ash
1.5 Litres warm water
60 mls Green Goddess Unscented Castile Soap

Put the soda ash into your bucket or sprayer then add enough warm water to make it up to 1.5 litres, make sure all of the soda ash dissolves into the water then add the dish wash liquid and mix to combine. Spray or pour on weeds on a fine, dry day and leave. The longer this solution remains on the noxious plants, the better its effect, the dish wash will help the solution stick.

This mixture will only keep for about a week so only make what you are going to use. It will go hard if left for too long.

Soda ash can also be used straight as a dry powder sprinkled between paving stones, on tiles or concrete. broom it in and add a sprinkle of water, then leave.

Photo credit for bottom pic Jenny Marvin


Comments 14

  1. How will the salt affect pets? I would like to use this on my gravel driveway but my cat and dog walk across it and I know they can Absorb things through their paws. Will this be safe?

    1. Post

      Hi, Soda Ash on your driveway will be fine for your pets paws in this recipe. It’s also used as an anti-caking agent in some food types and in some litter box formulations, be careful you don’t inhale the particles though.

    1. Hi Barbara, thats a very good question, I’ve not tried it but Wendyl said she was sure it’d work (see below). Please let us know if you have success. I’d try it myself but we’re lucky not to have any. Triona

      From Wendyl “I’m planning to plant a wildflower meadow but have a big problem with the kikuyu which the locals tell me I’ll never kill off without using a severe herbicide, which I won’t use.
      So I started thinking about my good friend soda ash and how last year I created an excellent weed killer out of. I got a tub of soda ash and mixed it with warm water, sprayed some weeds on the driveway and when I came back up this week they were all dead. My friend Ritchie who mows my lawns couldn’t believe it. “You’re onto something there,” he said.
      So, we’re going to use it to kill off the kikuyu in the meadow and I’m confident it won’t harm the soil.”

  2. Hiya,
    What part does the soap play? Just helping adhere? We use hand made bar soap for our dishes but we do keep a bottle of ecostore dish liquid just in case. Would these eco friendly soaps be enough or do we need to go out and get some stinky Palmolive to do the trick?


  3. Hi triona and grant
    I was thinking about spraying this on some weeds around some feijoa trees will this get into the soil and affect the feijoa trees or does it have to get directly on them to have any affect?

    1. We cut the foliage off and then spray so that it can get into the roots easily, they will die if it’s left on and not rained off.

      1. Just thought I should mention, we do leave a little foliage so that the spray attaches to it and travels down the plant, but we cut off the main part.

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