By growing something with roots, adding microbes (if there is some reason to think they are absent), and by adding organic fertilizer. The plant will send sugars to the roots and out into the soil for the microbes to eat. The protein on the surface will give the microbes something to use to multiply with. Somewhere in the 100,000 different species of microbes living in the soil, various acids are produced. Among them are humic acids, amino acids, and carbonic acid. But they only do this when they are healthy and well fed.

A way to do something similar is to use glauconite (called greensand for the gritty texture and dark green color). Greensand has a lot of different elements mixed in it. The end result of microbial activity on the greensand is that the soil becomes more acid.

What are you trying to grow? And where are you?

I'm in zone 6, Ma

Trying to grow scallions, lettuce, string beans, basil, strawberries

Sprinkling wood ashes around would be an organic way to make soil more alkaline. That is assuming that the burned trees were organic or close to it (some pesticides would probably survive the hot fire intact, but I imagine many wouldn't.)

I just fling my wood ashes around the orchard, it is supposed to be good in my slightly acidic soil, and also a bit of fertilizer. I spread it very thinly. I have heaped some up on dogwood that I am trying to kill to see what effect it will have.

Marcia

Oops I already know how to alkify - you use limestone

But what about organically acidifying?

Is Gypsum organic?
Is agricultural sulfur organic?

If not, what is organic that will acidify my soil (no, I dn't want to use peat moss, so that's not an option)

Lime (raise ph) and sulphur (lower ph).

Both are approved for organic production by the National Organics Standards Board

http://www.ams.usda.gov/nop/NOP/standards/ListReg.html

Here is a link that might be useful: NOSB Standards list

Start with a good, reliable soil test that tells you why your soils pH is where its at, because that will give you an indication of what to add to your soil to correct the problem. Do not guess, and do not add "something" in the hopes it might correct the problem because that kind of amending soils will most often cause more problems than it will cure. Contact your county office of the UMASS Cooperative Extension Service for more information.

Just keep adding a good compost and you'll get balanced enough to grow what grows reasonably well in your area. IMHO the only reason to add alot of any product to change your ph is if you are in a big hurry, want to grow something that really is out of ordinary for your area (like blueberries out here on the plains where I live), or don't want to put out that much compost for over a good length of time.

This post is ancient but somehow came up in my search. As an FYI you can acidify soil naturally by mulching in maple leaves.

That's not exactly correct. A lot of tree leaves are acidic when fresh but they lose that acidity as they begin to decompose. Just like compost. At best you can get some minor pH alteration in the top inch or so of the soil, but no deep or long term change. The acidity in the leaves isn't strong enough, doesn't last long enough and most soils resist pH changes via buffering.

There's quite a lot of literature on this topic out there if anyone cares to research it.

You need to add something that has 'persistence'. Maple leaves can work, but you would need A LOT, continuously, for a very long time. The acids would have to react and dissolve (and neutralize) whatever substrate mineral which was keeping the soil alkaline. That takes strong acids and persistence. The real problem with maple leaves is that factor of persistence. There really isn't anything to a leaf. It's dust. The mass of a leaf is quite nearly nothing (relatively speaking.) The mass of a pile of leaves is nothing... still relatively speaking.

Other acids, such as liquids, do not necessarily work well because they are highly water soluble and simply wash away. So, the keys are persistence, mass, and time. Drainage can work for and against your efforts. As discussed, acids are water soluble. They wash away. That works against persistence and time. However, drainage also helps take away the dissolved alkaline minerals.

Balancing drainage with the desired reaction is necessary. These reactions also create salts. BAD for gardening. Drainage...GOOD for gardening.

Take a pile of baking soda... an alkaline environment. Pour vinegar over it... watch the reaction. Eventually, the reactions stop. Keep adding vinegar while washing away the neutralized baking soda, and guess what, your finished environment is now acidic. The run-off consists mainly of salts.

I've been reading these forums for a short time now. Some here are incredibly sharp on many subjects. But this issue is one where there needs to be more understanding of chemistry. While in real world conditions it is indeed difficult to change the pH of a soil, it is NOT impossible, and it can be beneficial to the desires and needs of the grower.

Organic matter, Maple leaves, tends to make soils more neutral rather than more acidic. Maple leaves (pH of 3.2) are more acidic than Oak leaves (pH 3.8) but once the Soil Food Web works on them they become more neutral. The same thing happens in the compost pile so compost will have a pH more toward neutral.

A study done by Abigail Maynard, PhD in soil science, at the New Haven Ag Research Station in New Haven, Conn found that after years of adding Oak Leaves and Pine needles the soil pH was not significantly affected, by them.

kimmq is kimmsr