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Friday, February 17, 2012

KNOL: What is Garden Soil PH? Alkaline or Acidic? What Does it Mean?

Transfered from Google Knols to be stored on my blog.

Your garden soil has a PH value that determines whether or not the soil is on the acidic side, alkaline side, or relatively neutral. Vegetables and other plants do have a preference for soil PH but it is often a range. This is a good thing. Generally speaking you want your garden to have a neutral PH. This Knol will answer all your questions about garden soil PH.

What is Garden Soil PH?

What is Alkalinity? What is Acidity?

Neutralizing the Fear of Garden PH
by Gary Pilarchik LCSW-C
To learn more about vegetable gardening visit my very active blog The Rusted Vegetable Garden

What is Garden Soil PH?

Garden soil PH is the measure of soil acidity or alkalinity. Actually, I read it is technically a measure of hydrogen-ion concentration in the soil. Sometimes PH levels are also known as sour and sweet soil. The value of your soil is measured by a number on a scale of 0.0 (most acidic/sour) to 14.0 (most alkaline/sweet). A neutral value, which unlike Chinese food is neither sweet or sour, is 7.0 (neutral).
The optimal range of PH for a vegetable garden is generally 5.5 to 7.0. PH is mostly a concern for gardeners because values outside the optimal range can cause problems with nutrients in the soil. Specific ranges may effect how soil nutrients are available to your vegetable plants. Acidic PH levels, for example, may cause certain nutrients to quickly leech out of your soil. Or your vegetables may not be able to absorb or access certain minerals and nutrients. The most important factor to remember is that the optimal PH range of 5.5 to 7.0 allows the soil to work best with your vegetable plants. That range is the goal.

How to Make Garden Soil More Alkaline (Increase PH)

If your soil is acidic or slightly acidic you can make it more alkaline by adding a lime. Lime basically contains calcium. Calcium will increase alkalinitiy. On a side note calcium if also good for your tomatoes. The best type of lime to use is pulverized lime. Be cautious breathing in the dust and water your garden down after you mix it into the earth. It can take up to 90 days for the soil to react with the lime and reduce acidity levels or increase alkaline levels, depending how you prefer to look at it. Lime use is the easiest method to increase PH.

How to Make Garden Soil More Acidic (Decrease pH)

Aluminium sulphate or sulphur is used to decrease PH and add acidity. Aluminium sulphate will increase the acidity as soon as it disolves into the soil. You must follow the directions carefully when applying aluminium sulphate. Another way to increase your soil acidity level is to use sulphur. Sulphur actually becomes sulphuric acid with the help of  water and nature. Unlike aluminium sulphate which is fast acting, sulpher can take several months. Peat moss is another way to very slowly increase acidity in your garden.

Don't Add Chemicals Without a PH Test

Don't randomly add chemicals to manipulate levels without a PH soil test. I do use peat moss which is acidic and I add some pulverized lime to it when I use it. They neutralize each other. I am not using these products to increase or decrease my soils PH. I am using them to add organic matter to my garden. However, I want the peat moss to be close to neutral when I add it into my garden, so I use some lime.

Using a PH Test Kit in Your Garden: One Tip

Garden soil PH test kits can be bought on line or at your local nurseries. I find they are cheaper on line. The test kits will tell you exactly how to test and measure the PH level. I want to stress the importance of taking a balanced measure. You don't want to dig only in one place in your garden and measure the PH. You want a good sampling of soil from around your garden. The best way to do this is to get a bucket and fill it with 5 hand shovel scoops of soil on a dry day. Mix the soil together well in the bucket. Use that soil for the PH test.

Do You Need to Test the PH Levels of You Garden Beds

Yes and no. If you are just starting a garden, the chances are your vegetables will grow just fine. If you plant in over worked soil or are starting a garden in a place where there is no grass or weed growth, you might want to test the soil.
A rule of thumb I use is to test my soil every three years. I did not test mine the first year. To better answer this question I would say, test your soil the first season and amend it accordingly. After the first test, test it every three years.
The other thing to keep in mind is that if you are adding a lot of bags of garden soil (not topsoil) from home improvement centers, you soil is probably just fine. These products are neutral to start. It just depends on how much you add to your garden. If you use raise beds like I do, you will concentrate these amendments to one spot. That is one benefit of raised bed gardening.

What PH Levels Do Vegetables Prefer?

They mostly prefer a neutral range of 5.5 to 7.0. Remember vegetables want to grow and adapt to ranges of PH. Here is a list of vegetables and PH preferences.
 This list comes from




Bean, pole






Brussels sprout




















Pea, sweet


Pepper, sweet










Squash, crookneck


Squash, Hubbard





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