The soil pH value is a measure of soil acidity or alkalinity. Soil pH directly affects nutrient availability. The pH scale ranges from 0 to 14, with 7 as neutral. Numbers less than 7 indicate acidity while numbers greater than 7 indicate alkalinity.
The pH value of soil is one of a number of environmental conditions that affects the quality of plant growth. The soil pH value directly affects nutrient availability. Plants thrive best in different soil pH ranges. Azaleas, rhododendrons, blueberries and conifers thrive best in acid soils (pH 5.0 to 5.5). Vegetables, grasses and most ornamentals do best in slightly acidic soils (pH 5.8 to 6.5). Soil pH values above or below these ranges may result in less vigorous growth and nutrient deficiencies.
Nutrients for healthy plant growth are divided into three categories: primary, secondary and micronutrients. Nitrogen (N), phosphorus (P) and potassium (K) are primary nutrients which are needed in fairly large quantities compared to the other plant nutrients. Calcium (Ca), magnesium (Mg) and sulfur (S) are secondary nutrients which are required by the plant in lesser quantities but are no less essential for good plant growth than the primary nutrients. Zinc (Zn) and manganese (Mn) are micronutrients, which are required by the plant in very small amounts. Most secondary and micronutrient deficiencies are easily corrected by keeping the soil at the optimum pH value.
The major impact that extremes in pH have on plant growth is related to the availability of plant nutrients or the soil concentration of plant-toxic minerals. In highly acid soils, aluminum and manganese can become more available and more toxic to the plant. Also at low pH values, calcium, phosphorus and magnesium are less available to the plant. At pH values of 6.5 and above, phosphorus and most of the micronutrients become less available.
The pH value of a soil is influenced by the kinds of parent materials from which the soil was formed. Soils developed from basic rocks generally have higher pH values than those formed from acid rocks.
Rainfall also affects soil pH. Water passing through the soil leaches basic nutrients such as calcium and magnesium from the soil. They are replaced by acidic elements such as aluminum and iron. For this reason, soils formed under high rainfall conditions are more acidic than those formed under arid (dry) conditions.
Application of fertilizers containing ammonium or urea speeds up the rate at which acidity develops. The decomposition of organic matter also adds to soil acidity.
To make soils less acidic, the common practice is to apply a material that contains some form of lime. Ground agricultural limestone is most frequently used. The finer the limestone particles, the more rapidly it becomes effective. Different soils will require a different amount of lime to adjust the soil pH value. The texture of the soil, organic matter content and the plants to be grown are all factors to consider in adjusting the pH value. For example, soils low in clay require less lime than soils high in clay to make the same pH change.
Selecting a Liming Material
Homeowners can choose from four types of ground limestone products: pulverized, granular, pelletized and hydrated. Pulverized lime is finely ground. Granular and pelletized lime are less likely to clog when spread with a fertilizer spreader over turf areas. The finer the grind of the limestone the faster it will change the soil pH value. Hydrated lime should be used with caution since it has a greater ability to neutralize soil acidity than regular limestone.
Time of Application and Lime Placement
Lime needs should be determined by a soil test. Soil samples should be taken in the fall for the succeeding year’s garden. If test results indicate a need for limestone, it can be applied in the fall or winter months. Generally, for best results, limestone should be applied two to three months prior to planting to allow time for it to neutralize the acidity.
The most important factor determining the effectiveness of lime is placement. Maximum contact of lime with the soil is essential. Most liming materials are only slightly soluble in water, so incorporation in the soil is a must for lime reaction. Even when properly mixed with the soil, lime will have little effect on pH if the soil is dry. Moisture is essential for the lime-soil reaction to occur. In the case of lawns, it can only be surface applied and watered into the soil.
Wood Ashes
Wood ashes can be used to raise the soil pH. They contain small amounts of potassium, phosphate, boron and other elements. They are not as effective as limestone but with repeated use, they can drastically raise the pH value of a soil, especially if the soil is sandy in texture. Ashes should not come in contact with germinating seedlings or plant roots as they may cause damage. Spread a thin layer during the winter and incorporate into the soil in the spring. Check the soil pH annually especially if you use wood ashes. Avoid using large amounts of wood ashes because excessively high pH values and subsequent nutrient deficiencies may result. Coal ashes do not have any lime value and may actually be acidic dependent on the source.
Many ornamental plants and some fruit plants such as blueberries require slightly to strongly acid soil. These species develop iron chlorosis when grown in soils in the alkaline range. Iron chlorosis is often confused with nitrogen deficiency because the symptoms (a definite yellowing of the leaves) are similar. Iron chlorosis can be corrected by reducing the soil pH value.
Two materials commonly used for lowering the soil pH are aluminum sulfate and sulfur. These can be found at a garden supply center. Aluminum sulfate will change the soil pH instantly because the aluminum produces the acidity as soon as it dissolves in the soil. Sulfur, however, requires some time for the conversion to sulfuric acid with the aid of soil bacteria. The conversion rate of the sulfur is dependent on the fineness of the sulfur, the amount of soil moisture, soil temperature and the presence of the bacteria. Depending on these factors, the conversion rate of sulfur may be very slow and take several months if the conditions are not ideal. For this reason, most people use the aluminum sulfate.
Both materials should be worked into the soil after application to be most effective. If these materials are in contact with plant leaves as when applied to a lawn, they should be washed off the leaves immediately after application or a damaging leaf burn may result. Take extreme care not to over-apply the aluminum sulfate or the sulfur.
You can use the following tables to calculate the application rates for both the aluminum sulfate and the sulfur. The rates are in pounds per 10 square feet for a loamy soil. Reduce the rate by one-third for sandy soils and increase by one-half for clays.

Pounds of Aluminum Sulfate to Lower the pH
Desired pH 6.5 6.0 5.5 5.0 4.5
Present pH
8.0 1.8 2.4 3.3 4.2 4.8
7.5 1.2 2.1 2.7 3.6 4.2
7.0 0.6 1.2 2.1 3.0 3.6
6.5 - 0.6 1.5 2.4 2.7
6.0 - - 0.6 1.5 2.1

Pounds of Sulfur to Lower the Soil pH
Desired pH 6.5 6.0 5.5 5.0 4.5
Present pH
8.0 0.3 0.4 0.5 0.6 0.7
7.5 0.2 0.3 0.4 0.5 0.6
7.0 0.1 0.2 0.3 0.4 0.5
6.5 - 0.1 0.2 0.3 0.4
6.0 - - 0.1 0.2 0.3


If I want to buffer the PH in my soil I use dolomitic lime. :slight_smile:

I have never had to increase my soil PH

I have a $20 electronic soil tester (3 prongs and a slide switch for fertility/off/PH)… I’m thinking I should return it because EVERYTHING I test has the same PH as water… apple cider vinegar, katchup, and coca cola as well.

Not sure if I’m going to bother with another tester… If I start with new dirt- neutral for the most part, shouldn’t I be able to tell PH up or down just by looking at the plant…?

Soil probe testers don’t work well, or at all, in pure liquids, and the probes need to be kept polished, or buffed shiny for best readings in the soil, you can use a rough or coarse paper towel or something similar, you don’t need to buy some special super fine grit sand paper or anything like that, crumpled dull coarse newspaper would likely work as well. Also the soil should be moist enough the moisture meter reads the high or very wet side of the meter.


I hear ya…mine does the same thing lol…and I to have learned to read the plant and i’em getting good at it to.
I’em thinking maybe a few more grows and i’ll have this growing thing down pat.
In time i’ll just be cloning from clones



I would not want to leave my PH level to chance. Find a decent PH pen. PH is IMO; The most important aspect to achieving success. :smile:

BTW; Yeah, that tester is bad if you are not getting any different readings.

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How accurate do I need to measure dirt…?


The Etekcity® pocket-sized pH meter digital pen, with advanced technology and imported components, greatly reducing the volume and costs, maintaining their good quality, is born to be popular. Featuring high stability, reliability and usability, it’s suitable for users of all ages in various conditions.

Pure water production and consumption, electroplating liquid, swimming pool water, fluid photography, laboratories, aquaculture, food processing, home, office, teaching physics and chemistry, cosmetics ionized water, municipal water supply…


  1. Immerse the electrode in standard buffer solution (under the temperature of 25℃), and gently shake the electrode.
  2. Regulate the trimmer with the screwdriver until the buffer solution value corresponding to the measurement temperature is obtained.


  1. Measuring range: pH 0.0 - 14.0
  2. Resolution: 0.1pH
  3. Accuracy: ±0.1pH (at 20℃/68℉)
  4. Typical EMC DEV: ±0.2pH
  5. Battery: 3*1.5v (AG-13 button battery)
  6. Operating temperature: 0℃to 50℃ (32℉- 122℉)
  7. Relative humidity: ±95%
  8. Life: Approx. 700 hours of use

[Etekcity® 0.1pH High Accuracy Pocket Size pH Meter][1]

$13.68 amazon

No Bluetooth… :cold_sweat: (8. Life: Approx 700 hours of use) and looks like no parts to get too for cleaning.

So, let’s say you have a mother-in-law, and aside from making your life hell, needs to tell you how to do… everything you need to be doing… And you decide to take it out on her plants (just being funny)… so you mix in some aluminum what ever to make her soil way more acidic… what are the plants going to do to signal for help…?

Then, since you blew your chance at better karma… your cat eats all your lower leaves, knocks over a jar of lime, and works it all into the soil… Are you going to know right away like over feeding/watering…? or is a bad PH only going to show-up at the end of your grow being much less than it could have been…?

And could,“Critical PH” be something that should be part of a strain description…?

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What type of tester meter should I get ? One that mite just work, cause i’em tired of wasting my money on tester’s that won’t work for sh–.
I’em sure their out there some where but I just don’t know which one I can depend on.
Like you said Latewood ( can’t leave ph to chance ) I have over 40 plants in 3 gal buckets and each one can’t read the same ph no way and I keep it clean

Thanks for your help on this ( Both of you )


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Forgot to add… I bookmarked, liked, and will use all the info you provided here.

O.K. so your PH is off… up or down, are you going to see a cry for help, like over watering/feeding…? Or is it more of a poor result of your finished grow…?

Thank you, I also have my super guide to Sick Plants. it’s quite largei and made it into 2 parts that are in ZIP form
If you would like to take a look @ it I would be more than happy to e-mail to you.

As for the ph up or down I need to find a meter that is dependable.
The plants will tell you that something isn’t right that’s when I brake open my Complete guide to sick plants it also has pic’s to help you match up on what mite be wrong and how to fix it…pretty awesome.



I would really appreciate it if you would email your super guide to sick plants to me.
Diff something I need in my growing arsenal

Wow 4 year old post. Who knew :joy:

Could I also have your guid to suck plants? I am currently struggling with mine. They should have been done flowering by now, but I’m stuck in veg stage trying to bring them back. I’ve managed to keep them going, but not fully recovered.

Sorry I meant sick plants lol .


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