Acidity of spaghnum peat moss

Asked January 2, 2019, 5:47 PM EST

I would like to use some hardwood ash (I’m aware that ph of peat moss is 4-4.5) in my spaghnum peat moss/vermiculite for starting seedlings this coming spring (in containers) but I cannot find a formula anywhere on how much to use. I was just going to use a tablespoon or so but I decided I better check first. I am only using a 2.2 cubic ft. bag of peat for the project. Any suggestions on a proper amount to use? Thank you.

Washtenaw County Michigan

1 Response

It is difficult to make a blanket recommendation on the amount of hardwood ash to add without knowing the exact pH of the spaghnum peat moss or the neutralizing value of the hardwood ash. Is it possible to send a quart of the peat and 2 cups of the hardwood ash to the lab for pH analysis of the peat and to see the effect of the ash addition on the pH of the peat? For $20 I would be willing to do this analysis. Please email me directly at with what you decide to do. Thank you.
P.S. Are these vegetable seedlings you are starting?