apwh (04/27/83)
Adding organic material to the soil is usually the recommended way to increase the pH other than the addition of aluminum sulfate or other inorganic materials. Decaying vegatation produces organic acids which lower the pH. This is the reason there is more talk of sweetening soil. Heavily worked garden plots tend to get lots of compost, which lowers the pH. For small areas I've read that coffee grounds are especially effective, but for a 3000 sq.ft. garden you'd have to be one heck of a coffee drinker.
rej (04/28/83)
Oak leaves have a lot of tannic acid. Pine needles are also acidic. Therefore, compost including either of these will be quite acidic. I have found that needles take quite a bit longer to decay then oak leaves, so oak leaves make better compost.