Q: Can you spread a vinegar and salt solution under big pine and oak trees to kill the underbrush below them?
A: Neither vinegar nor salt will kill the underbrush. Concentrated acetic acid, which smells like vinegar, might burn the leaves off the underbrush but it will re-sprout quickly. Salt could possibly kill the shrubbery if you put down lots of it…but if you apply enough salt to kill the underbrush, you’ll hurt the tree roots as well. Acetic acid and sodium chloride are twice as toxic as glyphosate (Roundup). Why not use glyphosate sprayed on the leaves of the underbrush to kill it? If you’re looking for an organic option, a sharpened shovel or a heavy mattock will do a great job removing the woody plants you don’t like.