GigZ-16's pH guide

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Newbies pH Guide.

What is pH?

pH is the measure of how basic or acidic a solution is. The pH of a substance is measured in a numerical fashion using a scale of 1 through 14. A solution with a pH higher than 7.0 is considered to be basic and is called a base (or alkaline). A solution with a pH less than 7.0 is considered to be acidic and is called an acid. The strength of an acid or base can be either weak or strong. The stronger an acid or base, the closer the solution is to its respective number on the pH scale (basic being 15 and acid being 1). The weaker a solution or base, the closer its pH value is to a neutral rating (neutral being 7). Every full point change in pH signifies a 10 fold increase or decrease in acidity or alkalinity. For example, water with a pH of 6.0 is 10 times more acidic than water with a pH of 7.0, while water with a pH of 5.0 is 100 times more acidic than water with a pH of 7.0.

Here are some examples of acids and bases and their respective pH ratings.
-.2 Battery Acid
1.2 Gastric fluid
2.2 Lemon juice
3.6 Orange juice
4.4 Beer
5.6 Pure Rain
6.6 Milk
7.0 Distilled water (H2O)
8.0 Seawater
9.2 Baking soda (NaHCO3)
10.6 Milk of Magnesia (Mg(OH)2)
11.4 Household ammonia (NH3)
12.8 Household bleach (NaClO)
13.6 Household lye (NaOH)

What is PH? pt. 2

pH is defined in chemistry in several ways. An acid is sometimes defined as a solution with the potential to donate a Hydrogen ion (H+, also called a proton), or to accept a Hydroxide Ion (OH-) from a base. A base on the other hand is sometimes defined as a solution with ability to donate a Hydroxide Ion, or... you've guessed it, accept a Hydrogen ion. Low pH corresponds to a high hydrogen ion concentration and vice versa, while a high pH corresponds to a high Hydroxide ion concentration and vice versa.

Why is pH important when growing a plant?

Any substance that is going to be used to support any form of life has to fall within a certain range on the pH scale. The range may vary from organism to organism. Marijuana is no different. The soil, nutrient solutions and water all need to be monitored and adjusted to stay within a specific range, depending on your method of growing. When growing Marijuana in soil, the soil and water supply should stay within the range of 6.5 to 7.0, while in hydroponics the nutrient solution should stay within the range of 5.5 and 6.8 (5.8 to 6.3 being optimal).
When a plant's soil or nutrient solution becomes too basic the nutrients become unavailable to be absorbed by the roots. When the soil or nutrient solution becomes too acidic the acid salts will chemically bind together the available nutrients and they will be nonabsorbent by the roots. When this happens the plant will show tell-tale signs of stress. Some novice growers and even a few seasoned growers will falsely think they need to add more nutes or fert, which only compounds the problem by usually causing toxic salt build-up. Toxic salt build-up stops the roots from absorbing water. So remember as a rule of thumb to always test the pH before reducing or increasing a fert or nute dosage!
The pH of your soil or hydroponics setup can be measured with a simple 20$ or 30$ pH Tester, or small one time paper tests. These are highly recommended when growing any plant.

Some things to remember when using an electronic pH tester

1. Clean the probes of the meter after each test and wipe away any corrosion.
2. Pack the soil tightly around the probes.
3. Water soil with distilled or neutral pH water (7.0) before testing.
4. The meters measure the electrical current between two probes and are
designed to work in moist soil. If the soil is dry, the probes do not give
an accurate reading

What causes fluctuations in pH?

When growing in soil any fertilizer you use can cause an excess build up of salts when it decomposes in the soil. This almost always results in a more acidic soil which stunts the plant's growth and causes brown foliage. When using a Hydroponics set-up the nutrient solution can very easily cause a fluctuation in the growing reservoir. Other common reasons as to why soil may become too acidic when doing outdoor grows are rainfall, leaching, organic matter decay and a previous harvest of a high yeild crop in the same soil. In dry climates, such as the desert Southwest US, Spain, Australia, etc., irrigation water is often alkaline with a pH above 7. The water in rainy climates, such as the Pacific Northwest of North America, the UK, Netherlands and Northern Europe, is often acidic with a pH below 6. Lightly sandy soils with little clay and organic matter are quicker too become more acidic. Another common mistake is that a grower will mix his soil unevenly, leading to "hot spots" in the growing medium, so mix all ratios as well as you can.

How do I raise/lower my pH?

A great way to regulate the pH of your soil is to use Dolomite Lime(calcium-magnesium carbonate). While growing Cannabis plants in containers, mix one cup of fine dolomite lime for each cubic foot of soil, then lightly water it. After watering, mix it once more and wait a day or two before checking the pH. While growing in an outdoor garden, follow the dolomite lime manufacturers instructions. Dolomite Lime works well because it has a neutral pH rating of 7.0 and tends to keep the soil a constant pH throughout the entire life cycle of the plant. This is a highly recommended method of regulating your soil pH.
If you find the pH of your soil or Hydroponic reservoir to be too acidic or basic you could add either pH up or pH down. These are chemicals sold at places like Home Depot or any Gardening store. They usually come in one liter bottles and are to be diluted in the water used to water the soil growing plants or the Hydroponic reservoir according to directions on the packaging.

Some examples of Home remedies to raise/lower pH are as follows:
1.Lemon juice. 1/4 tbsp can bring a gallon of tap-water from 7.4 to 6.3.
2.Phosphoric acid. lowers pH and provides Phosphor too!
3.Nitric acid. lowers pH.
4.Hydrochloric acid. strongest way to lower pH
5.Hydrated lime. flush soil with a teaspoon per gallon of water to raise pH.
6.Baking Soda. eats acids to raise pH.
7.Calcium carbonate. raises pH (very strong)
8.Potassium silicate. raises pH.

What are signs of a PH fluctuation in my Cannabis plant?

A Cannabis plant can show signs of a pH flux in several ways. The leaves may begin to turn yellow or brown, dry up and/or shrivel on the sides into a straw like shape. Keep in mind however that other deficiencies and disorders may show the same signs of damage, so don't jump to conclusions until you do some testing and adjusting to your plants and their growing medium.

Some things to remember(I didn't write these ones)

1.Always test the pH of raw water and drainage water with a pH meter.
2.Raw water pH above 6.0 helps keep fertilizer mixes from becoming too acidic.
3.The pH level is much more important in organic soil gardens than in chemical
hydroponic gardens. The pH dictates the environment of bacteria necessary to the
uptake of organic nutrients.

I hope I helped at least one or two people.


In any case, soil gardeners have been told certain plants require acidic conditions- for example, rhododendrons and azaleas- or else they won't grow. The solution advocated by most experienced gardeners is not dissimilar from what a hydroponics grower would do: adjust the pH with chemicals, such as agricultural lime, to make the soil more alkaline. To make alkaline soil more acid, we are told to add sulfur. Because they are chemical changes, these solutions work for a short time. But to me pH is a biological matter.

A bit of quick pH review is in order (if only to make amends for the mistake in my book). You may remember that pH is a measure of the acidity or alkalinity of a solution on a scale of 1 to 14; 1 being most acidic and 14 being most alkaline. A more technical description is that pH is the measurement of the concentration of hydrogen ions, H+. If you have lots of H+, the pH is low, or acidic. If you have few of them, the pH is high, or alkaline.

If you are adding fertilizers and using chemicals, you are stuck in the chemical realm. Organic gardeners, soil food webbies in particular, realize that pH has more to do with biology than it does with chemistry. That's because of the way plant roots take up nutrients. Root hair surfaces are covered with positive electrical hydrogen cations. Think of these charges as ping-pong balls. If soil particles are small enough, their surfaces are covered by these ping-pong ball charges, both positive (cation) charges and negative (anion) charges. These cations are not limited to hydrogen; they also include calcium, potassium, sodium, magnesium, iron, and ammonium. All are important plant nutrients.

When a root encounters a clay or organic particle, it can exchange one of its hydrogen cation for another positive one from the particle. It can choose from calcium, potassium, sodium, magnesium, iron, ammonium and hydrogen, as these are all cations carried by clay and silt and are all, as luck would have it, major plant nutrients.

This is known, incidentally, as cation exchange capacity, or CEC. Sand and silt have low CECs, because they comprised of particles that are too large to hold electrical charges. This is why humus and clay are needed to make soil good. They are extremely small particles and can carry cations.

So, back to pH. Every time a plant root exchanges a hydrogen ion for a nutrient ion, it increases the concentration of hydrogen ions in solution. Thus, the pH goes down and things should become more acidic.

Ah, but things usually balance out because the positive cations on the root surface also attract negative charges. Here, hydroxy ions (OH-) are the exchange ping-pong balls, and addition of hydroxy ions lowers the concentration of hydrogen ions in the solution, and pH goes up.

I know this still sounds like chemistry and not biology. However, each plant has an optimum pH requirement. What soil growers need to know (and hydroponics growers don't) is that the type of bacteria and fungi attracted to a plant's rhizosphere by the plant's exudates has a lot to do with setting this optimal pH. Bacteria produce a slime that raises the pH, and fungi produce acids that lower the pH. Since the plant is in control of the biology it attracts, in a natural system, it is the plant that determines the pH, and not some chemistry teacher.

So, while you may forget the chemistry of pH, at least remember there is a biological side. Do no harm to it, and you shouldn't have to worry much about pH when you grow plants in soil. Moreover, the nutrient exchanges that occur above also have a lot to do with what kind of bacteria and fungi are attracted to the root zone as some like higher pH and others lower pH.


Wow guys, I personally think both of these compliment each other well. Furthermore, I think they should be considered for the GrowFAQ Contributions section. Keep up the awesome work guys!
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