Increase pH to proper level and your garden will flourish

By Bev Johnson | The Daily Journal

Published Saturday, February 16, 2008

Do you know the pH of your soil? Do you even know what the heck pH is?

The chemist's definition is "a number expressing the acidity or alkalinity of soil equal to the logarithm to the base of 10 of the reciprocal of the effective concentration of hydrogen ions." OOOooof!

In plain English, pH stands for power of hydrogen. The pH scale goes from 1 to 14 with 7 being neutral. The higher the concentration of hydrogen ions in the soil solution, the lower the pH. Easy to remember.

Just think of vinegar. It is 5 percent acid. Lower than neutral. One step on the scale, for instance from six to five means that the soil that measures five is 10 times as acid as the soil measuring at six. Most plants grow best in the 6 to 7.5 range. Soil in Otter Tail County runs alkaline, seven and up.

Because plants take up nutrients only in solution, the pH of that solution determines what dissolves and what doesn't. For instance, iron and aluminum dissolve in acid soil perfect for blueberries, but deadly for tomatoes. This is why soil sulfur is used to acidify soil.

It helps the soil release iron. Not enough iron and leaves turn yellow.

Too much rain, think Seattle, washes the calcium, magnesium and potassium out of the soil making it acid. Not enough rain and calcium and other bases predominate making alkaline soil. You can temporarily modify the pH of your soil by adding sulfur or limestone but it will revert quite quickly.

Compost acts as a buffer helping to keep soil pH stable by binding to plant nutrients and holding them until they are needed. Even if you don't have a formal compost pile, sheet composting will help your soil.

A layer of leaves tilled in or in a flowerbed, just piled on and left to rot, will lead to healthier plants. In the spring, simply dig a trench in the garden and bury your food scraps — no meat or the dogs and raccoons will dig it up. By the fall, they will have rotted and can be tilled in.

So how do you find out what the pH is of your soil? Simple. Come into the Extension office and get a bag for your soil and an information sheet on how to sample it.

You send it in to Minneapolis with $15. They do all the work, send you back a list of what you need to add, the amount of compost in your soil and the pH.

Knowing the pH of your garden will make you a better gardener. Just think of the fun you can have at those coffee klatches.

"What's the pH of your garden? You don't know? No wonder you have those little tomatoes."