Soil pH Basics

A pH value indicates how acidic or alkaline something is on a scale from 1 to 14. Pure rainwater or distilled water is neutral with a pH of 7.0. Acids have pH less than 7 (lemon juice and vinegar are around pH 2). A pH above 7.0 is more alkaline (baking soda is around pH 8, ammonia is about pH 11).

Most vegetables like a neutral or slightly acidic soil (pH 6.0-7.5). In areas with wet, rainy climates like the Pacific Northwest, soils tend to be acidic. Soils with lots of leaf matter also tend to be acidic, as do clay soils. So the soil in your Seattle garden is more likely to be slightly acidic than alkaline - but don’t worry, it might not be too acidic.

Simple Soil pH Tests

Here are a few basic pH tests. These test are not exact by any means, but should give you a general idea of whether your soil pH is too far from neutral. If either test indicates your soil is too far from basic, you should get a more accurate test from an expert, or try the mild corrective actions mentioned.

To test if your soil pH is too low (acidic, also called sour): Add a pinch of baking soda to a tablespoon of wet soil from your garden. If you don’t hear a lot of fizzing, then your soil is not too acidic (try testing for alkalinity). To correct acid soil, add a few scoops of lime, dolomite lime, or even wood ashes to your plot and dig it into the top few inches of soil.

To test if your soil pH is too high (alkaline, also called basic or sweet): Add a tablespoon of white vinegar to a tablespoon of dry soil from your garden. If you hear fizzing, then your soil is probably too alkaline (try testing for acidity). If you don’t hear a lot of fizzing, then your soil is not too basic. To correct slightly alkaline soil, dig peat moss into your planting beds.

Copyright © 2003 Brian Ballard. All rights reserved.

When Your Garden Sleeps, It Dreams

This winter it may seem nothing is happening in your garden. Biological activity slows down in the colder months, organisms go dormant or migrate deeper into the soil, cool season weeds like chickweed get their first footholds, and rains wash nutrients and important minerals away. You don’t have to be a helpless observer of this hibernation. Use the winter months to rebuild your soil.

Once your garden is done for the season, clear out the last of your annual plants saving them for compost. Reserve a small part of the garden for your fall and winter greens and for planting garlic cloves in November. Cover the rest of your soil with a nice layer of compost materials about 8-12 inches deep. Be sure to use both “greens” (grass clippings, coffee grounds, fresh chopped plants, composted manure) and “browns” (fall leaves, non-pressure treated sawdust, dry plant material) in the mix.

A variety of amendments help replenish the supply of important minerals. Agricultural lime is a good source of calcium, and dolomite lime also includes magnesium. Calcium helps plants build cell walls. Magnesium is the working ingredient in chlorophyll. Both types of lime help neutralize acidic soil, which is also a side effect of too much rain.

A compound called greensand includes a different mixture of beneficial minerals including potassium, iron, and phosphorus. It’s usually available at better garden centers.

You can even use granite dust to add a wide array of minerals to your soil. If you look closely at granite, you’ll notice it’s made up of thousands of different crystals fused together. Each crystal is essentially a different mineral, including many that plants require in tiny amounts: potassium, calcium, iron, magnesium, phosphorus, manganese, and others. These minerals become more available when ground into gravel, or even into dust, and are broken down further by organisms and naturally occurring weak acids in the soil. Ready sources of granite dust include stone yards, or gravestone monument carvers.

Spread a few handfuls of lime, greensand, or granite dust over your compost mix and work it in a bit. Water the mulch well, and cover it with two layers of burlap. The burlap works as insulation, keeping the soil and sheet mulch slightly warmer than the air, and provides the dark, moist environment soil organisms prefer. Most coffee roasters will gladly give you discarded burlap bags their raw coffee beans are shipped in.

Once or twice during the winter, pull back the burlap and turn your compost mix, covering it again with the burlap when you’re done. In the spring, you should be able to remove the burlap and either plant directly into the finished compost, or work it into your soil a bit if it’s not completely done.

Copyright © 2006 Brian Ballard. All rights reserved.