Choosing a Mulch - Knowledgebase Question

Burlington, NC
Question by mom_witham5
August 11, 2007
You guys gave me such good advice on my new excursion into composting. It has been going well, and there is lovely compost in the bin.

Next we planted some crape myrtles in the yard and we want to mulch them, but aren't sure what type of mulch to use. Can different types of mulches affect the pH of the soil? If so, what type of pH do crape myrtles prefer?

One more thought...what types of things would affect the pH of the compost? We are doing a lot of canning and our compost is full of cucumber, pepper (sweet through habanera), and tomato scraps, and some corn, and of course coffee grounds.

Hope I'm not asking too much. Thanks.

Answer from NGA
August 11, 2007


Glad we've been so helpful in your composing expedition. Whether or not your compost is completely finished, you can use it to mulch around your crape myrtle trees. It will continue to decompose while it is slowing evaporation and suppressing weeds.

You can continue to use both green and brown (nitrogen and carbon rich) materials in your compost. As you keep turning it and mixing it, everything will break down and the pH of the finished compost will probably be close to neutral. Just fyi, the pH in a compost bin changes during the process: A pH between 5.5 and 8.5 is optimal for compost microorganisms. As bacteria and fungi digest organic matter, they release organic acids. In the early stages of composting, these acids often accumulate. The resulting drop in pH encourages the growth of fungi and the breakdown of lignin and cellulose. Usually the organic acids become further broken down during the composting process. If the system becomes anaerobic, however, acid accumulation can lower the pH to 4.5, severely limiting microbial activity. In such cases, aeration usually is sufficient to return the compost pH to acceptable ranges.

Best wishes with your compost!

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