Beside this, what is the best material to put under a deck?
Does vinegar kill weeds permanently?
Removing the soil or grass from below your deck may seem a good idea, but this leads to drainage problems. The grass may eventually die off due to lack of sunlight filtering through the deck, but the remaining topsoil still drains water faster than if you dug out the entire area.
wild edges The north west of south east Wales Posts: 6,793
Just on the glyphosate vs vinegar question: acetic acid is a herbicide. Household vinegar is usually a fairly weak solution of acetic acid. Glyphosate is thought to be potentially carcinogenic but in tests it is LESS toxic to animals than acetic acid (less likely to kill you immediately if you drink a glass of it). Vinegar is less effective as a herbicide, therefore to get the same effect you will have to use more of it and anyway, it’s effectiveness against a perennial weed such as couch grass is doubtful. I don’t know whether vinegar or glyphosate is more harmful to bees and pollinators but to your soil and it’s ecosystem, by the time you’ve actually had an impact on the couch grass, the vinegar is likely to do more harm.
raisingirl East Devon, on the Edge of Exmoor. Posts: 5,013