Chelsea Christenson wrote:

My master gardener suggested a solution of vinegar and water for
killing the weeds that come up between the bricks in my patio.
Unfortunately, she's on vacation now, so I can't ask her: what is the
correct ratio of vinegar to water?

Household vinegar is not registered as a herbicide and has minimal effect
on the control of weeds. Yuu might get some top dieback of young weed
seedlings but the roots will be unaffected and it will have no apparent
effect on larger, more established weeds.

Household vinegar is only 5-7% acetic acid - any dilution will reduce that
concentration further. Registered herbicidal applications of vinegar are a
by-product of the wine making industry and are 20% acetic acid (and
typically contain high concentrate citric acid as well) and are extremely
caustic, not to mention expensive (about $50 per gallon). Caution should
be exercised when using - not only because of the causticness but acetic
acid is also very non-selective - it will affect any plant in the vicinity
of the application. At that concentration, it changes the soil pH (at
least temporarily) to the extent that most plants find the soil too acidic
and unhospitable for growth. It is NOT fast acting - the label suggests up
to six months for noticeable results - and the soil may require
remediation before it is acceptable for planting.

It also has a very adverse effect on soil biota. Personally, I'd choose
another method of weed control.

pam - gardengal