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”
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