lower soil ph cannabis

Understanding pH and How It Affects Cannabis Plants

In the world of cannabis growing, pH affects and is affected by everything. Indeed, the entire process of growing plants is a study in the physical dance of pH balance. Read on for an in-depth overview of pH as it relates to growing quality cannabis.

While it can be a daunting topic to try and wrap your head around, understanding soil pH is key to growing healthy cannabis plants. In this article, we’ll outline all you need to know about soil pH and how to get it right when growing weed.


What Is Soil pH?

pH is a measure of how acidic or alkaline something is. The pH scale ranges from 1–14, with a pH of 7 being neutral (the pH of pure water). If pH is lower than 7, a substance is considered acidic (think vinegar or lemon juice). If the pH is higher than 7, the substance is alkaline, as is the case with soaps, bleach, and ammonia.

In more scientific terms, pH level has to do with the concentration of hydrogen ions, say in the water you give to your plants. The pH scale is logarithmic to the base 10, which means that water with a pH of 6 is already 10x more acidic than water with a pH of 7.

Below is a basic chart of the different pH levels of common items:

1.0 – Battery acid
2.0 – Lemon juice and vinegar
3.0 – Orange juice and soda
4.0 – Tomato juice
5.0 – Black coffee and bananas
6.0 – Urine and milk
7.0 – Pure water, not tap or bottled water
(the pH running or bottled water can vary considerably)
8.0 – Seawater and eggs
9.0 – Baking soda
10.0 – Milk of Magnesia and the water of the Great Salt Lake, Utah

Why Is pH Important When Growing Cannabis?

So, you now know what pH is. But how exactly does the pH of your growing medium affect the growth and health of your plants?

As you already know, all plants require nutrients for healthy growth. They require the macronutrients nitrogen, phosphorus, and potassium, as well as micronutrients and minerals including calcium, magnesium, iron, copper, and a whole lot more. If plants cannot access these nutrients, it will lead to deficiencies and other serious health problems.

The issue with cannabis plants is that they are only able to take up nutrients within a small pH window, which ranges from about 6–7 when growing in soil. If the pH is lower or higher than that, the plant cannot take in nutrients, even if they are present—thus spurring nutrient deficiencies via “nutrient lockout”.

In those places where cannabis thrives in the wild, the soil is normally slightly acidic; therefore, homegrown cannabis plants also prefer a slightly acidic environment. However, the way that you grow cannabis also plays a role in the optimal pH level for your plants. Cannabis grown hydroponically or without soil needs an even lower pH than a soil grow.

The Benefits of Maintaining the Perfect pH

The benefits of caring for and maintaining your plants’ pH is pretty straightforward; you’ll have healthier plants that demonstrate more vigorous growth and, as a result, produce better harvests. Plus, you’ll also ensure that the time and money you’ve spent fertilising your plants is paying off.

By regularly checking the pH of your growing medium, you’ll be able to ensure that your plants are able to take up all the nutrients you’re giving them. You’ll also be able to catch any pH imbalances early, minimising your risk of running into nutrient deficiencies later on in your grow (more on that below).

The Problem With pH Imbalances

pH imbalances are one of the most common causes of nutrient deficiencies in cannabis plants. As we mentioned earlier, cannabis plants can only take up certain nutrients within a small pH window. If the pH of your medium shifts below or above that ideal window, your plants won’t be able to take up the nutrients in their fertilisers and will start to show signs of a nutrient deficiency.

Understanding and Preventing Nutrient Lockout

Nutrient lockout (sometimes referred to as “nutrient lock”) occurs when your cannabis plants can’t absorb nutrients from the soil or the fertilisers you’re using to feed them. One of the primary causes of nutrient lockout is pH imbalance, but it can also be caused by salt buildup near the root zone as a result of feeding with mineral fertilisers (which tend to have a high salt content).

The Best pH for Growing Cannabis

We’ve alluded to it already, but the best pH for growing cannabis resides within a narrow window. But, within that window, is there an optimal reading you should try to achieve? And, does that reading change depending on how you choose to grow? Let’s explore further.

Soil pH Chart: 6.0–7.0

If you grow in soil, the optimal pH level for the root zone is between 6.0 and 7.0. However, there is no set number within this range that is “best”. Instead, it can be good to allow for some natural fluctuation within this window to support optimal nutrient uptake.

So, as you adjust, try a slightly different reading each time. You can, for example, adjust your pH to 6.2 for one watering, then 6.6 the next. As long as it stays within 6.0–7.0, you should be fine. Soil is also more forgiving when it comes to pH imbalances, but it can only give so much.

If you grow purely organically—where you do not administer mineral nutrients—pH is less of an issue. If you’re using amended or composted soil with organic matter, the microorganisms within will make the nutrients more available to the roots. However, most growers using standard potting mixes and mineral nutrients will indeed have to reckon with pH.

Go Organic and Forget About Measuring pH

At RQS, we’re big proponents of organic cannabis growing; not only because it delivers a far superior product, but because it takes some of the hassle out of growing, especially when it comes to pH.

While using chemical nutrients might seem simple, it can actually take some time and practice to get the hang of properly fertilising your cannabis plants with liquid mineral fertilisers. Organic nutrients, on the other hand, naturally promote the health of your plants by supporting the development of healthy microbial life within your medium.

Using natural fertilisers like compost, worm castings, and bone meal creates a breeding ground for healthy bacteria and fungi that keep the conditions of your soil optimal, so there’s usually no need to monitor the pH of your soil as closely as you would otherwise.

Hydroponics and Soilless pH Chart: 5.5–6.5

Hydro and soilless grows are a different beast when it comes to pH. If you grow soilless, say in coco, the optimal pH level at the root zone should be somewhat lower than in soil, between 5.5–6.5. The same goes for all methods of hydro.

With these methods, it is just as important that you allow the pH level to fluctuate across the acceptable range to support nutrient uptake. For example, in hydro, calcium and magnesium are mostly absorbed at pH levels above 6, while other nutrients like manganese prefer a slightly lower pH.

Then again, this shouldn’t be an issue since pH levels will naturally fluctuate slightly with each feeding in a hydroponic setup. You will only need to correct if the pH level exits the optimal 5.5–6.5 range.

When growing in coco, perlite, or hydroponically, you are in charge of administering nutrients directly to the root zone via the water, which means huge pH fluctuations are more of a risk than in soil. The inert media used in hydro and soilless grows merely retains water and provides support for the roots. So, when administering nutrients, be careful that you don’t overload your plants.

How to Test Cannabis Soil pH

Managing pH level means testing the water or nutrient solution and adjusting it accordingly. This may sound complicated, but it really isn’t.

To test pH, you can use a digital pH meter or a pH measurement kit with drops. Opinions here differ as to which method is “best”. Some prefer digital pH meters because they are accurate and easy to read, while others like the drops as they are super simple and don’t require calibration. Try them both and see which you prefer.

Cannabis pH — FAQs

Let’s break down some of the most common questions related to cannabis pH. Feel free to refer to these if you encounter any pH-related issues during your grow.

Questions & Answers: Ph

🧪 Do I Test the pH of My Fertiliser Before or After Adding My Nutrients? Always measure the pH after you add any nutrients or amendments as they will change the pH value of your water. After you mix your nutrient solution, use a pH meter or drops to test its pH level.

If you are growing hydroponically, test a sample from your water reservoir a few minutes after you add your nutrients. 🌊 Do I Need to Measure the pH of My Runoff After Feeding My Plants? Yes. Always remember to test the pH of your nutrient runoff as this will give you an idea of the pH of your medium. 🌈 How Exact Do I Need to Get My pH Levels When Growing Cannabis? Don’t get flustered if your nutrients are slightly below or above the optimal conditions we mentioned above. Only react to big changes in pH that may inhibit your plant’s ability to uptake nutrients.

Measuring pH With Drops

pH measuring kits usually contain a test tube, a bottle of testing solution, and a colour-coded pH chart. Testing the pH of your soil with these kits is super simple:

  1. Prepare your fertiliser as per usual and stir it gently. Be careful not to over oxygenate your fertiliser as this may throw off your pH reading.
  2. Half-fill your test tube with your fertiliser and add 3 drops of testing liquid into it.
  3. Gently shake the test tube to mix the pH testing solution with your fertiliser.
  4. Use the colour chart to read the pH of your fertiliser and, if needed, use pH up/down products to adjust it.
  5. Repeat this process with the runoff from your fertiliser. If the pH reading from your runoff is far below or above that of your fertiliser and in the danger zone (below 5 or above 7), you may need to regulate the pH of your soil.

Measuring pH With a Digital pH Meter

Measuring pH with a digital pH meter (like our pH tester) couldn’t be any more simple. After you’ve calibrated your device, simply stick it into your fertiliser, runoff, and soil to get an accurate reading of the pH in your garden.

Struggling to wrap your head around pH? Click here for an in-depth overview of how pH affects your cannabis plants, whether grown in soil or hydro.

How 2 Lower PH in Soil..

New Member

i have a ph in my soil of around 7..

i need to know how to get it lowered so i dont hafta worry bout it anymore..

ive posted b4 n no one gave me the right answer i was lookin for..

so hear we go again to see what happens..

thanks for adive..

New Member

All you need to know and then some.

New Member
Active Member
New Member
New Member

i have a ph in my soil of around 7..

i need to know how to get it lowered so i dont hafta worry bout it anymore..

ive posted b4 n no one gave me the right answer i was lookin for..

so hear we go again to see what happens..

thanks for adive..

causes of ph fluctuations and pH facts.

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 have a ph in my soil of around 7.. i need to know how to get it lowered so i dont hafta worry bout it anymore.. ive posted b4 n no one gave me the…