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How To Fix Alkaline Soil and Raise PH Levels In Soil

PH Soil Levels

Importance of Soil PH

How To Change PH Levels In Cannabis

You’ve tested your soil and found that your PH levels are either too acidic or alkaline. Now, what are you going to do? How are you going to fix this problem? Well, don’t worry, in most cases, it is not that hard to either raise or lower your PH levels to acceptable levels. However, if not done right, you can ruin your cannabis yield or severely limit the size of your harvest.

I will now go over the steps that need to be taken to either raise or lower the soil PH levels to make sure that your soil is not too acidic or alkaline.


For your reference, the top chart illustrates the various PH levels and how raising or lowering PH will make your soil either alkaline or more acidic.

 Soil PH Testing Options

There are two methods of testing soil PH that are most commonly used by marijuana growers, which are detailed below:

  • Test Strips: These are simply strips of paper, which change color with the corresponding color representing various PH levels. Test strips are the least accurate way to measure PH levels.
Garden Tutor Soil pH Test Strips Kit (3.5-9 Range) 100 Tests

PH Test Strips

  • Handheld PH Meters: Are used directly in your grow space where you submerge the probe electrodes into either water or soil and then read to meter to find out the PH level. The handheld meters resemble either a pen or a bike tire pump.

Apera Instruments AI209 Value Series PH20 Waterproof pH Tester Kit, ±0.1 pH Accuracy

Click the following link to find out how to choose the best PH Testers and Meters.

How To Raise PH In Soil

You will need to raise the acidic level of your soil and make it more alkaline if the PH level is less than 5.5. The most common way to increase the PH levels is to add limestone to your soil. The two types of limestone that are most commonly used for raising PH are calcitic limestone, which is primarily composed of calcium carbonate, and dolomitic limestone. Both kinds of limestone work equally well. However, dolomitic limestone also adds magnesium to the soil, which can be bought in the following forms: pellets, hydrated, granular, and crushed. To use the limestone, you simply work it into the soil. The following is an overview of the various type of lime available.

  • Crushed Or Pulverized Limestone: Crushed limestone is the preferred choice for newbie cannabis growers, who need to raise the PH levels and make their soil more alkaline. The reason for this is that crushed limestone works quickly, and it is also safer for your plants. The main downside to crushed limestone is that it tends to clog fertilizer spreaders more easily. However, most indoor growers of cannabis will not need to worry about using a fertilizer spreader. For quickest results, look for the finest grounded limestone that’s available.

Dolomite Lime - Pure Dolomitic/Calcitic Garden Lime (5 Pounds)

  • Pellets Or Granular Limestone: Pellet limestone is spread more efficiently with a fertilizer spreader; However, the limestone pellets also take a long time to break down into the soil. Since spreading your limestone via a fertilizer spreader is not needed for a smaller indoor marijuana growing operation, granular limestone should not be your first choice for raising soil PH.

Hoffman 15208 Pelletized Garden Lime, 8 Pounds

  • Hydrated Limestone: Hydrated limestone is the fastest method for making the soil more alkaline. The downside to using hydrated lime is that too much-hydrated lime can ruin your plants. Therefore, to be safe, beginning cannabis growers should stay away from hydrated lime or only experiment with hydrated lime on a single plant.

Voluntary Purchasing Group Fertilome 33371 Horticultural Hydrated Lime, 5-Pound

How To Lower Your PH Soil Level

If your PH level is more than 6.5, you will need to lower the PH level for your soil to make it less alkaline. Like with acidic soil, to lower the PH soil level, you will need to add fertilizer, which can be done by merely using mulch and compost-enriched soil. Also, you do not even have to buy your soil as you can use soil enriched mulch from your outdoor garden. As a result, all you have to do is transfer your prepared soil, from your outside garden to your indoor cannabis growing operation. The downside to using your own, enriched soil from outside is that it takes a long time for the mulch and compost soil to lower the PH. But, regular mulching and composting will eventually make your soil less alkaline.

Other methods for raising the acidity of your soil is listed below:

  • Elemental Sulfur: Adding elemental sulfur to the soil is the most straightforward and typical way to lower PH levels. Sulfur is inexpensive, spreadable, and moderately safe to handle. A significant drawback of elemental sulfur is that it takes a long time for the sulfuric acid to make your soil less alkaline. How quick it will work depends on the following: a.) How small are the sulfur grains. b.) How much soil moisture is present. c.) Temperature of the soil, and any bacteria that may be present. The time at which sulfur will start working to lower PH depends upon the above, and it even can take up to a month for the sulfur to be absorbed into the soil and for it to start working its magic. As a result, aluminum sulfate instead of plain elemental sulfate is most often used to reduce the PH.
Elemental Sulfur

Elemental Sulfur

  • Aluminum and Iron Sulfate: Aluminum and iron sulfate act very fast in lowering the alkaline levels in your soil. However, use aluminum and iron sulfate soil can be damaging if it is overused, and be extra careful to make sure that any aluminum or iron sulfate does not come into direct contact with the leaves, and if they do come in contact, you need to be sure to wash off the leaves thoroughly.
  • Fertilizer Containing Acidifying Elements: Adding fertilizers, which contain elements, such as, ammonium nitrate, amino acids, ammonium sulfate, or sulfur-coated urea will raise the acidity of your soil. However, this is not a quick fix, and it will take time for the PH levels to be decreased.