Q. Have you ever heard of adding vinegar or citric acid when fertilizing indoor plants in our area? We collect the rain water and use it for our indoor plants.
A. Quite a few people do this to lower our water’s alkalinity but the effect is short-lived. Our tap water carries a lot of calcium and magnesium salts. The acids are neutralized by these and other salts.
|Diagrammatic representation of pH scale|
as found at
Numbers are logarithmic so each unit
change represents a factor of 10 (e.g.
6 to 7 = 10; 6 to 8 = 100; 6 to 9 = 1000)
similar to the same scale used for
measuring earthquake intensity.
You could determine how much acid to add fairly simply by using some pH litmus paper, like they use for swimming pools. You would add small amounts of acid until you see a shift in the pH of your water into the acid range.
The perfect pH is 6.8 which is the pH of the plant sap of many plants. Let this water/acid mixture sit for 30 minutes or so and check it again. Keep adding small amounts until you see the pH stay steady in that 6.8 pH range then you can use it for watering.
As long as you stay with the same water source, you would add the same amount of acid each time to arrive at basically the same pH. If you change water sources, then you would have to do it all over again.
However, as soon as you pour this mixture on our soils it will shoot back up again to the alkaline range because of the massive amounts of alkaline types of minerals that reside in our soils. In short, I wouldn’t waste my time doing this unless it helps you sleep better at night.
Just adding a big scoop of good compost to your water instead of vinegar will probably do more good. Let the compost steep for a few hours through a porous sock like old pantyhose. Use it immediately for watering. Put the spent compost around some outdoor plants or in your garden. Good compost is likely to still have gnats so don’t apply the spent compost to the soils of indoor plants.