The Q&A Archives: controlling pH

Question: How can i control the pH level in my outdoor vegetable garden. i've been using mixture of soilless mix/shrimp compost/rotted manure, but have had problems regulating the pH from season start (near 7.0) to season end (around 5.5). What can I do? Is there an organic alternative?

Answer: To some extent the answer depends on the normal pH of your soil and that of the amendments you are already using, so you might want to run some basic soil tests to check those as a basis for adding additional amendments. In the garden, ground limestone is a good form of soil sweetener to use because it is available to the plants over a long period of time, slowly dissolving over a period of years. In addition, plants will generally tolerate some fluctuation in pH over time, with the "neutral" being a goal rather than an absolute. As a rule of thumb, to raise your pH one point add about 30 pounds of ground limestone per 1000 square feet of sandy soil, 50 pounds on loam, and 80 pounds on heavy clay. If you spread it in the fall on freshly worked soil it will work its way through the soil over the winter in time for spring. Be sure to spread it evenly as it does not spread but rather sinks into the soil. As a quick fix in mid season, you might consider using a dusting of wood ashes, but you will find that the wood ashes leach out very quickly and need to be repeated in much smaller and more frequent doses.

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