My question is on where it says for a quick fix water plants several times with vinegar, 2 tablespoons in a gallon of water. How much is several times? Also, can I use it on plants that are in the ground?
How to Raise Acid Level in Soil
Certified GKH Gardening Expert
I would say watering with vinegar "several times" means two or three times. Vinegar can be used to tweak the soil pH temporarily, but the effect isn't very long-lived and it probably can't be used to make drastic changes in soil pH. Vinegar works best in container plants, because soil microbes are thought to consume the vinegar when it's added to plants growing in the ground.
This article provides other options for lowering soil pH: