The Correct Soil pH For Herbs

Soil pH is not usually a worry for herb gardeners who plant in containers and pots because the compost we buy from the garden centre has a balanced mixture of nutrients that create a neutral to slightly alkaline pH level.

Knowing that might prompt you to ask, “Why bother to learn about it then and what is it anyway?”

Because having an understanding that whatever you mix in the soil or water your herbs with has a pH of its own and therefore can harm or enhance your plant`s environment.

You won`t be so quick to listen to any Tom Dick and Harry who claims that some crazy concoction will boost their growth and make them tower like Jack`s beanstalk!

What is pH?

I am not going to try and explain in a mind-boggling scientific way but will try to put it in a much simpler fashion.

First, the letters pH stand for “potential of Hydrogen “ or a measure of the hydrogen ion concentration of a solution.

When you mix potting soil with water and measure it with litmus paper it will turn a shade of green indicating a low concentration of hydrogen ions. On the pH scale this will be between 7 to 14.

The higher the number the bluer the green will become. Cold colours!

7 is neutral so the lower the number the more acidic the solution will be with high concentrations of hydrogen ions. The lipnus paper will turn yellow, then orange or red. Hot colours!

A high concentration of hydrogen ions will impede a plants ability to absorb certain nutrients that is why the soil pH should be slightly alkaline for most herbs. You won't find many soils below 5 or higher than 8.

Herbs That Like High Soil pH

Most herbs are happiest in soil that is around pH 7 ½ - 8 which is slightly alkaline or basic, but they will tolerate slightly more or less.

If you have a small garden patch for your herbs and they are not doing so well try giving it a top layer of compost or add a little lime or chalk but not too much.

You can also do this with pots and containers if you have a plant that really likes more base soils. For example: Mints, Lady's mantle, Lemon Verbena, Pyrethrum, Chicory, Clove Pink, Wild strawberry, and Hyssop all love alkaline soil.

Herbs That Like Low Soil pH

The acidity of the soil for plants that like a low pH are on the scale of 7 – 5. To lower it add alfalfa meal but use very little until you see improvements.

For example: Gardenia, Kaffir Lime, Foxglove, Yellow Gentain, Witch Hazel, and Dog Rose all love slightly acidic soil.

How to Test Soil

With a Meter

For the purpose of getting a rough guide on the soil pH of a small herb garden whether in pots or in a small plot, a two pronged meter will suffice.

I bought one and played around with it and it does give a good indication.

All you need to do is push the prongs down into the soil and leave it there for a few minutes. It will then give you a reading on the pH scale.

On the dual prong type the monitor has a moisture and light gauge which is great for knowing if your soil is too dry or too wet but how measuring the light can beat your own eye clocking I will never know!

The following pics are the results of the pH meter testing. I have posted them for those who want to see the results of my testing.

Click on the pictures to see them enlarged in the gallery.

With Litmus Paper

I tried litmus paper. It was great when it came to checking the pH of the water source but the water greatly influenced the testing of the soil.

Pics to show that the litmus paper was working. Dipped one in ammonia smelling salts which is totally alkaline, and one in malt vinegar which is totally acid.

Amonia shows blue indicating high alkalinity and vinegar shows red indicating high acidity.

The following pics are the results of testing both sources of water which marked a big difference. Tap water with chlorine added made it more alkaline than the water butt source.

But when I tested the soil with each of water sources the results showed the same colour range as you can see in the last picture.

I did the test with compost and the results were the same.

In the last picture left is the soil and butt water results and right the soil and tap water results.

Below the right strip is the butt water and left the tap water. Sorry got them the wrong way around!

What did this test accomplish? At least I know my soil and compost are alkaline!

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