If there’s one thing you should know about your vegetable garden, it’s the soil pH. The pH scale runs from 0 to 14, with 7.0 being neutral. Measurements between 0 and 6.9 are acidic, and those between 7.1 and 14.0 are alkaline. The target vegetable garden pH is 6.5.
Soil pH is important because…
1. pH is so important to plant growth because it determines the availability of almost all essential plant nutrients. At a soil pH of 6.5, the highest number of nutrients are available for plant use. See the USDA chart below for a visual explanation.
2. If the vegetable garden pH is too acidic, certain nutrients become less available, phosphorus in particular, while other nutrients, like aluminum and manganese, can become toxic. Acidic pH levels are also unwelcoming to beneficial soil bacteria.
3. Alkaline soils impede the availability of nutrients like iron, manganese, copper, zinc, and also phosphorous. Plants dependent on high levels of iron, evergreens in particular, perform poorly in alkaline soils.
Related post: 6 things every new vegetable gardener needs to know
How to adjust pH of your soil:
The only way to tell if your garden soil pH needs to be adjusted is to get a soil test. These are available in the U.S. from the Extension Service of your state’s land-grant university. Here’s a link to determine where to go. There are also a number of independent soil testing laboratories. In Canada, check with your local agriculture office. A garden pH test is not expensive and should be performed every four or five years.
1. Acidic soils are amended with lime to raise the soil pH and make the soil less acidic. The exact amount of lime necessary to properly adjust pH can only be determined by a soil test. Do be aware, however, that not all liming materials are equal. Look to your soil test results to determine if you need calcitic lime or dolomitic lime.
– Calcitic lime is mined from natural limestone deposits and crushed to a fine powder. It is also called aglime or agricultural lime and supplies calcium to your soil as it adjusts the pH.
– Dolomitic lime is derived in a similar manner but from limestone sources that contain both calcium and magnesium.
If your soil test comes back showing high levels of magnesium, use calcitic lime. If the test shows a magnesium deficiency, then use dolomitic limestone. Pelletized forms are easier to use and allow for more uniform coverage, and the application rate for pelletized lime is lower than for crushed. A 1:10 ratio is the rule of thumb. Meaning you need ten times less pelletized lime than crushed agricultural lime to garner the same pH change. So, if your soil test recommends adding 100 lbs of crushed agricultural lime, you can add 10 lbs of pelletized as an alternative.
2. If you’re growing acid-loving plants, such as evergreens, blueberries, rhododendrons, and azaleas, you may need to lower the soil pH into the acidic range. If this is necessary, turn to elemental sulfur or aluminum sulfate.
– Elemental sulfur is applied to the garden and is eventually oxidized by soil microbes. It takes a few months to adjust pH. Working it into the soil will yield better results than adding it to the surface because it is more rapidly processed when it’s mixed into the soil. Spring applications are generally the most effective. Elemental sulfur is often found in pelletized form, and while it may take some time to work, it is far less likely to burn plants than aluminum sulfate products.
– Aluminum sulfate reacts quickly with the soil and makes a rapid soil pH change, but there is an increased potential to burn plant roots.
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Soil pH maintenance:
It’s important to remember to only add the recommended amount of any pH adjusting product as per the results of a soil test. Adding too much may shift the pH too far and cause a different set of problems.
Because both lime and sulfur will eventually be processed out of the soil, the pH will revert to a less-than-ideal level every few years. To keep the vegetable garden soil pH at the optimum 6.5, a new soil test should be performed in the vegetable garden every four to five years.
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Do ph soil testers like the one in your picture work? So why a soil test at a lab if they do?
They are not consistent and you get what you pay for. Two-pronged models that are of good quality are pretty reliable, but they cost more than most people want to spend. Plus, a laboratory soil test will give you lots of other useful information aside from your pH, such as nutrient content, cation exchange capacity, organic matter content, etc.
Hi, I keep reading that the 4.5 pH is what we should aim for with our blueberries. The catalogs and companies that sell the blueberries say the same thing. But if you have a pH meter at home, try testing the soil that they send the blueberry shipped in. Every Blueberry that I buy the pH is right around 6.5. Why is that? It seems they Blueberry people themselves have trouble achieving that acidic goal. I can put Sphagnum moss around my bushes, ph adjuster, fertilizers for acid loving plants such as blueberries, hollies, etc… and do this several times a year. Put my coffee grounds, And still, I can never get my soil below 6.0. It will always creep back up. But having said all of that, the Blueberry bushes do not seem to mind the 6.5 pH that they are growing in. I also give alfalfa pellets for a boost and soil conditioner as the earthworms pull the pellets underground. My bushes are loaded and look beautiful. I live in West TN, and an occasional ring of horse manure shows up too. Still they maintain between 6.0-6.5. I spoke with other ladies at a garden club and we got into a discussion of our blueberries, and they all pretty much said the same thing. That their bushes stay around the 6.0 and a little above. All of my bushes are Rabbit Eye, except I have one that was a Northern Blueberry, and was doing poorly up next to my house, and moved it to my blueberry patch. Now it is really beginning to shine. I am anxious to see if it blooms again after moving it and how it will do. I do water when the ground gets dry as well. Thank you for the pH soil videos.