The Q&A Archives: Raising Soil pH

Question: I understand lime takes a long time to raise soil ph. Is there anything that works quicker? I have heard that wood ashes work quickly. If not, I've heard that hydrated lime works more quickly than regular lime. Is that simply lime mixed with water, and if so in what proportion?

Answer: Raising soil pH depends on what type of soil you have and what materials you use; however, most established plants would object to a very quick change. If the required change is not terribly drastic, then lime will work gradually but quickly enough, since most plants will tolerate a fairly wide range of pH values and plants that have been suffering will respond dramatically to even a slight improvement. It also lasts for several years.

In addition, one of the easiest ways to buffer pH in a hurry is to add copious quantities of organic material such as compost, rotted leaves, or well aged manure and bedding. This is easy to do in the vegetable garden, more difficult around established plants. Finally, if you are trying to make a drastic pH change for ornamental plants you may need to rethink your plant selection -- if they require constant fiddling with the soil pH they may not be the best choice for your area.

Quick lime is not a very good choice for garden use because if too little moisture is available it will burn the plants and it will also deprive the plants of nitrogen. Hydrate of lime can also burn plant roots as it leaches so quickly and is not recommended. Wood ashes also leach very quickly (and should never be used near acid-loving plants) and can vary in analysis. Ground limestone is still the best choice because it moves slowly and is thus available to the plants over a longer period of time.

Pulverized limestone or dolomitic limestone are the best to use, and will work more quickly if worked into the top 4 to 6 inches of soil although they are usually spread on the surface in the fall. Remember too that it is as bad to overlime as to underlime.

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