Adjust Your Soil Acidity

Wimpy zucchini? Listless legumes? Pathetic peas? Your garden's pH may be off-kilter

Soil acidity can make or break veggie yields, but luckily for you, it’s fairly easy to adjust. On the fourteen-point pH scale, anything below pH 7.0 is acidic; anything above it is alkaline. For vegetable gardens, you want your dirt mildly acidic — pH 6.0-6.5 is the safest range — although potatoes and yams prefer more acidic conditions, while artichokes and mushrooms like their dirt more alkaline. (Web sites such as and list pH ranges for specific crops.)

Cheap and easy pH test kits are available from many nurseries and hardware stores. You put a bit of dirt in a test tube, add the test solution, wait, and bingo — the liquid changes color according to pH. Some nurseries will even test soil samples for free.

Lowering Soil pH

So now that you know your dirt is all wrong, how can you fix it?

East Bay soil has a high clay content and tends to be alkaline, says Brian Gabbard of Berkeley’s Magic Gardens nursery, so if anything, you’re going to want to lower your garden’s pH. According to Gabbard, you shouldn’t have any problems if you condition your dirt well with organic soil amendments, which acidify the soil and improve drainage to boot. But you can also use inorganic sulfates. Magic Gardens carries a product called True Blue, which is aluminum sulfate. Other options include iron sulfate or magnesium sulfate (Epsom salts). The amount to apply will depend upon what type you use and how acidic your soil started out. In any case, you should thoroughly mix it into the dirt before you plant next spring. According to, sawdust, composted leaves, wood chips, cottonseed meal, leaf mold, or peat moss also help lower soil pH.

Raising Soil pH

On the off chance your dirt is too acidic, Gabbard says, you need lime –which can be sold as dolmitic, agricultural, or hydrated lime. suggests the following applications to raise soil pH by 1.0 point.

Sandy soils: 4 ounces of hydrated lime per square yard

Loamy soils: 8 ounces per square yard

Clay soils: 12 ounces per square yard

Peaty soils: 25 ounces per square yard

If your soil is seriously acidic, the site recommends adjusting pH gradually over several years, and testing again each year; you can also add hardwood ash, bone meal, crushed marble, or crushed oyster shells to lower the acidity.

Oh, yeah: Come time for the bountiful harvest, be sure and send your excess veggies to the author.

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