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.

Getting Creative with Compost Ingredients

There's no special trick to successful composting other than ensuring a good mix of greens and browns. But there is an endless list of things that might be good -- or might be wrong -- to add to your compost.

The Good

Though potentially off-the-wall, these items can actually increase the overall benefits of your compost:

• Clay - Soil should be a good mix of organics, sand and, yes, even clay. The clay in dirt can even help capture nitrogen (as ammonia) before it escapes from your pile. (Don't add modeling clay.)


• Egg shells - These add calcium to the soil. (Don't compost rotten eggs.)


• Granite dust or greensand - This adds several trace elements. You can get granite dust at tombstone manufacturers. (Greensand is just a term for rock dust.)


• Hair - This sounds icky to me, but human and pet hair contains lots of nitrogen and composts nicely I hear.


• Junk mail - This is the most satisfying thing to tear up and throw in a pile! (But see glossy paper below.)


• Oyster shells - Either whole or preferably crushed, these add calcium.


• Seaweed - Seaweed contains lots of nitrogen. Wash it down first to remove salt.


• Soil - Some gardeners like to jump-start their compost by introducing extra organisms from soil. Though all organisms needed for decomposition already exist on plant material, adding a few shovels-full of soil can't hurt.


• Wallboard or drywall - Crumble it up as much as possible, and don't over-do it! Drywall is made of gypsum, which includes lots of calcium.


• Wood ashes - Wood ashes from non-pressure treated wood are high in potassium and can be used sparingly in compost. Don't use more than one or two shovels-full per batch since ashes are very alkaline and will disrupt the pH of your finished compost. (But see below for coal or BBQ ashes.)

The Bad

These things can go into compost if you're really, really good at composting, but the average gardener should avoid them:

• Dairy products - Same issues as meat (below).


• Diseased plants - Your pile would have to get awfully hot to kill all viral pathogens. Bag diseased plants at your plot and take them home for disposal.


• Fat or lard - Same issues as meat (below).


• Human urine - Though urine from a healthy person is sterile and contains lots of nitrogen, don't include it at our community garden. You can give it a try in your home compost if you must.


• Meat scraps - It takes a very specific set of conditions to safely decompose meat or dairy products. It's very hard for the average gardener to reproduce these conditions.

The Ugly

Strictly verboten! Never ever, ever put these things in your compost. At best they won't decompose, at worst they may cause disease in humans!

• Animal urine, feces, or litter - Cat feces in particular can contain parasites that cause brain damage in toddlers, infants, or unborn children. (Pre-composted horse, cow, rabbit, chicken manure or manure from other vegetarian animals is fine to add to your compost.)


• Coal ashes - These ashes contain harmful chemicals, even after burning. Don't use BBQ grille charcoal ashes either.


• Glossy paper - Don't compost glossy paper, catalogs or magazines. They include special clays and inks that aren't the best for your soil. Don't compost paper with colored ink either.


• Human feces (including diapers) - Leave it to the city to try to figure out how to deal with your poop! It can contain all kinds of viruses, bacteria and other diseases like dysentery, e. coli, and cholera. Even composted human waste from municipalities should never be used on food crops.


• Metal, Plastic or glass - These items will simply never decompose. Broken glass in the soil is obviously dangerous to gardeners.


• Pesticides, herbicides or fungicides - These will kill the very organisms you're trying to encourage in your compost!


• Petroleum products - Liquid petroleum products will poison the soil and groundwater. One measly pint of gasoline can contaminate 750,000 gallons of water.


• Pressure treated wood or sawdust - Pressure treated wood contains cyanide and/or other chemicals that kill beneficial soil organisms.

More Reading

Lists of other things you can or should not put in your compost:

Compost Ingredients at MasterComposter

All About Materials by Steve Solomon

What can I compost? at the HDRA

Materials for Better Composting at the Chicago DOE


Copyright © 2003 Brian Ballard. All rights reserved.