The Q&A Archives: limestone

Question: I was told in my soil sample test results to use calcitic limestone. What is the difference in calcitic,dolomite and hydrated horticultural lime? Can I use the hydrated lime that I have? It says on the packaging (hydrated horticultural lime) that fall is the best time to use so it can leech in. I want to use it for this season,is this ok? thanks Jim

Answer: I would not recommend using hydrated lime. Although -- or because -- it is so fast acting, it is so strong that it can burn the plants' roots. Calcitic lime is mainly calcium carbonate. Dolomitic lime is mainly magnesium carbonate. They all work to raise the pH or make the soil less acidic.

The dolomitic lime is the slower acting type, but it is sometimes preferred because it adds magnesium to the soil. (Magnesium is one of the nutrients required in small amounts by plants.)

If your local county extension recommends calcitic lime then that is what you should probably use. You can apply it at any time, but be aware it will take time, as in a year or two, to show any results because it has to leach through the soil and that process is unavoidably a slow one.

If you need to make a major change in the pH it is better to apply it in smaller amounts over several years time than to apply it all at once -- a big change done all once can shock your existing plants. It is customary to lime in the fall, but you could do it in spring and fall. Once your soil reaches the desired target range, you should not have to apply lime again for several years. Then an occasional application, as indicated by soil tests, should be sufficient to maintain the pH at an acceptable level.

Your county extension should be able to tell you how much to use, depending on the type of soil you have (clay, sand, silt) and how much change you are aiming for.

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