Thursday, June 10, 2010

Fertilizer Friday Composting IV -- pH

It's Friday, and that means a visit to Fertilizer Friday over at Tootsie Time.
Check out her blog party and see what other people have blooming in their gardens.

This is my fourth post in my series about Composting. You can read the others here:

Composting I -What is Compost?

Composting II -Getting Started

Composting III -What to Compost

Composting Q & A

This week I am going to talk about pH.

I remember the first time I was introduced to the concept of pH. It was an ad back in the 70’s.

I can still sing the jingle, but I didn’t have a clue what pH balance meant, and I venture a guess that neither did most of the population.

Then, in the 80’s I worked at a swimming pool.

We had to test the chlorine level and the pH level every hour, and write the numbers down on a little chart.
Once a day, the maintenance guy would take the chart go and fiddle with the knobs and switches in the control room.

I still didn’t have any idea what pH was, I just knew that it had something to do with shampoo. And I knew that if the color of the strip was ever out of the “Safe” range according to the little chart on the wall in the lifeguard office, we were to call the Maintenance guy immediately. In fact, if it was ever more than one full number out of the “safe” range, we were to evacuate the pool. That never happened in the time I was there, but it was on the safety instructions posted on the wall in the lifeguard room.

So, I had heard the term a lot, but still had no idea what it was.

In the 90’s I took Occupational Food Safety classes at Virginia Tech, where I learned all about FAT TOM. No, he wasn’t a guy who worked there. FAT TOM was the acronym or mnemonic for the conditions necessary for bacteria to grow.

When we talked about Acidity, they gave us all kinds of facts and figures and numbers about pH levels and what was ideal and what was bad. I still didn’t know what the heck they were talking about, but I finally dared to ask. And I got a long confusing answer about logarithms and reciprocals and stuff. But I did finally learn that the “H” part stands for Hydrogen. OK, now I was getting somewhere.

One instructor said the “p” stood for “percentage“, another said it was for “parts” and still another said it was for “potential”. So maybe I didn’t need to feel so stupid for not knowing what it was.

But the best answer I got was that it really didn’t matter what pH stands for, but it was important what it represents. OK, I was on a roll here. Finally I was getting something I could use. So here it is, in normal people language.

pH is a term used to measure, or describe the amount or acid or acidity in a substance. Great, I can live with that. So pH means acid? Well, not exactly. The higher the pH, the less acid. The lower the pH, the more acid.

But it’s more than just that. Remember in science class when they taught us about acids and bases? Remember all the things we had to test with those little red and blue strips of paper? Remember having no clue what they meant when they said something was a base? Me too! But a base (or alkali) is the opposite of an acid. A really high pH level indicates something is a base. A low pH level means it is an acid.

For whatever reason, pH is measured on a scale of 0-14. Don’t ask me why, It’s all I can do to explain what. Why, is reserved for someone else.

A pH level of 7 is neutral. No acid, no base.

Just for info purposes, here are some common substances and where they rank on the pH scale.

Foodborne pathogens grow best in a pH between 4.5 and 7.5.
Now, in the restaurant industry you don’t want bacteria to grow. So you manage conditions so as to discourage them. Foods that fall between 4.5 and 7.5 are high risk foods and you make sure and treat them accordingly, keeping them refrigerated and away from some of the other FAT TOM elements.

In a compost pile, however bacteria are good things. The more they get in there and do their job, the faster the compost breaks down. So the ideal pH level for your compost is 5.5 to 8.

Interestingly enough, most plants will do best in soil that has a pH level of 6.5 to 7. But when you add a good quality compost to your soil, it broadens that and will allow your plants to thrive in pH levels from about 6 to about 8.

That’s another mystery for the science guys to explain…

What all this boils down to, is that we want our compost to be between 5.5 and 8.

But how do we control the pH in compost?

This is the really cool thing about composting. Most of the time we don't really have to do anything. The natural process of composting produces a substance with a pH level between 7 and 7.5 All you have to do is keep your pile balanced with browns and greens, and you will generally have a good pH level.

Now, there are some myths out there about pH in the compost pile and I want to address a couple of them now.

MYTH -Coffee is acidic, so coffee grounds will lower your pH level and the you have to add something to bring it back up.
FACT- Although Coffee is acidic, most of the acid is leached out of the grounds in the brewing process. Coffee grounds are mostly neutral. Adding brewed liquid coffee directly to your garden will lower your pH slightly, but coffee grounds will not, especially if they go through the composting process first.

MYTH - You need to add lime to your compost pile to counteract the acid in the food scraps you add.
FACT- Not only is lime not necessary, but many experts are now agreeing that adding lime may be harmful to your compost pile. Lime is often added to garbage piles or outhouses to reduce odor. It does this by killing certain bacteria and by converting nitrogen to ammonia. (it's a little more complex that that, but that is the main idea.)
It makes no sense to add nitrogen to your compost and then add things to destroy the nitrogen.

MYTH -You should attempt to make your compost either acidic or alkaline, based on the needs of your soil
FACT- If your soil need pH adjustment add it directly to your soil. Your compost should have the acidity level necessary to feed the fungi and protozoa and microbes and bacteria needed to compost, No matter what you add, you will either kill them, or they will produce compost that is roughly 7 to 7.5 pH. As a general rule, you will not significantly affect the pH of your finished compost by adding anything to it.

So, I hope I have helped you to understand what pH is, and how it comes into play when composting.

Next time we will discuss some more factors that affect your compost pile.
~{@ @}~ ~{@ @}~ ~{@ @}~ ~{@ @}~
Be sure and join me each Tuesday for Tuesday Trivia Tie-in, where readers are invited to share trivia and show off their treasures.
Read all about it here


  1. Troy you really explain all this to a normal person, thanks!!

  2. Very interesting post. thanks for the easy explanation. Are you an Occupational Health professional? Just wondering. My husband is a Safety Engineer.

  3. Great post, thanks for sharing. Have a great weekend.

  4. Troy, Really like how you put this article together. Like the "Earth Born" shampoo - I remember that - trip down memory lane and showing my age. lol Like the analagies with the pool. Having had a swimming pool for a number of years, I can identify with that. I am really enjoying your posts on composting. You do a very nice job.
    p.s. We removed the swimming pool in 2001 and we now have a huge flower garden where the pool used to be. It's debatable which is more work!

  5. Love this tutorial on composting - thanks for sharing, Paula in Idaho

  6. Very interesting. I'd love to take horticulture classes, but haven't the time right now. You feed this need. thanks

  7. Great lesson on pH. I actually understood everything :-)

  8. that was a lesson!!! Thank You Troy! I love learning from talk to us and entertain us while you teach us!
    I had a horrible epic failure the first time I tried to compost...but I have been thinking about it since you started this series...never know!!!
    Thank you for joining in today. I have very much enjoyed my visit...I hope you will join in again soon!