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Red Cabbage pH testing

Posted by g-in-fl 9a Florida (My Page) on
Sat, Mar 2, 13 at 12:35


If you designed this Red Cabbage Juice pH Test, you're a genius ! If you didn't, you are an Angel at the very least for sharing it!

And, you certainly were right to tell me to test the pH of my cow manure. I think I read somewhere that cow manure has pH around 5 - 5.5 and horse manure is around 6 - 6.5.

Well, according to the test, my cows did not read that post.

When compared to the baking soda sample, wouldn't you say it looks more like 7 or 8?

I have to buy more cabbage, and do some more tests now that my company has gone. But , I feel that I now have a very valuable tool which will keep me in a reasonable range when mixing amendments into my planting holes.

I THANK you, and my roses THANK you!

Gracin, Teas, Noisettes, and a couple Chinas and Musks

Follow-Up Postings:

RE: Red Cabbage pH testing

Hi Gracin:

I tested bagged cow manure, Moo-manure from HomeDepot, and it tested around 8, slightly less green than baking soda (pH 8.3). I googled for ingredients of bagged manure: lime is added to deodorize, to suppress weeds, and to supress fungal growth inside the bag.

One time I got bagged cow manure from Menards, it was horribly stinky, and sprouted weeds all over. My tomatoes loved the acidic manure and gave a bumper crop (my soil pH is 7.7). I still have to weed that spot constantly, after many years!! Fresh cow manure, if not treated by lime to deodorize, has a reported value of 4 to 5.

I learned about the red cabbage juice on-line and applied it to testing my soil, after wasting money on useless pH meter and soil-testing kits. None of the chemistry classes I took taught that, not even Organic Chem, nor Biochemistry. My major is Computer S., minor in chem.

I can see why lime is added to bagged manure. The horse manure I get is very alkaline, the stable told me they put lime to deodorize the enclosed stall in our zone 5a. I put excess manure in bucket inside my garage, zero mold.

Then I mixed peat moss (pH 4), alfalfa meal (pH 6) into the horse manure to lower its pH ... it sprouted this fuzzy white mold on top, pretty gross.

RE: Red Cabbage pH testing

  • Posted by catspa NoCA Z9 Sunset 14 (My Page) on
    Sat, Mar 2, 13 at 15:42


Using cabbage juice indicator to measure the pH of a variety of liquids is one of the standard labs for a non-majors Biology class I teach at a community college. Like you say, works pretty good, and you can't beat the price...


RE: Red Cabbage pH testing

Thank you, Debbie for the positive feed back.
Thank you, Gracin, for an excellent picture. I'm glad it helped you.

Red cabbage is also useful to test the SURFACE soil pH, to prevent fungal growth. I don't have blackspots on roses mulched with horse manure, even with the year with 49" rain, plus 32" snow. My horse manure pH is 7.5 in spring, and pH 8 in late fall.

My mediocre horse manure on woodchips bedding and lime has 2 advantages: 1) woodchips dries out faster than clay (staying wet longer means germinating fungi better). 2) Lime suppress fungal growth with its high pH and anti-fungal properties.

I tested the surface pH around roses in relation to fungal growth, and the degree of surface wetness, mixed in with my soil pH 7.7:

1) surface wet rotten tomatoes (pH 4.5) - worst blackspot
2) surface Hollytone with sulfur mixed in - equally bad
3) surface wet alfalfa meal (pH 6) - second worst BS

Wet decomposed leaves weren't bad, just a tiny bit of BS. University of Illinois documented the end result of decomposed leaves as slightly alkaline, and not neutral.

Here's a research which explains why bagged cow manure is reported as very acidic (pH 4), or very alkaline (pH 8).

Contrasting Soil pH Effects on Fungal and Bacterial Growth ��" 1 by Department of Microbial Ecology, Lund University, Sweden . 2. Soil Science Department, Rothamsted Research, United Kingdom. ABSTRACT
The influence of pH on the two principal decomposer groups in soil, fungi and bacteria, was investigated … This experimental location provides a uniform pH gradient, ranging from pH 8.3 to 4.0, within 180 m in a silty loam soil. ..

The growth-based measurements revealed a fivefold decrease in bacterial growth and a fivefold increase in fungal growth with lower pH. … Below pH 4.5 there was universal inhibition of all microbial variables."

Here is a link that might be useful: Cheapest way to test soil pH using red cabbage

This post was edited by Strawberryhill on Sat, Mar 2, 13 at 17:08

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