Alternatives to pH Down for Cannabis Plants

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What is pH?

Imagine that! You thought you’d try your hand at growing weed, so you invested in some seed and equipment, and now suddenly you’re learning all sorts of interesting things about photosynthesis, building manifolds, and fungal infections.

It kind of makes you wish you paid more attention in biology class, doesn’t it?

As it turns out, you should have been taking notes in chemistry class, too. That is, if you want to understand the importance of pH and its role in the healthy growth of your cannabis plants.

The term “pH” stands for potential of hydrogen or power of hydrogen – scientists can’t seem to agree. However, without getting too deep into the weeds discussing hydrogen ion concentrations, the important thing to understand about pH is that it is a measure of how acidic or alkaline something is.

On a scale of 1 to 14 where a pH of 7 is neutral, a pH level below 7 falls into the acidic category, and a pH level above 7 is considered alkaline.

Soil Nutrients and Solubility

Why is this important? Like all living things, plants need nutrients to grow.

They count on macro nutrients like nitrogen for help in the photosynthesis process, potassium for root growth and regulation of CO2 and oxygen levels, and phosphorous for the production of flowers and seeds. There’s also calcium, magnesium and a slew of micronutrients they can get from the soil.

If you grow your cannabis in soil, their roots will be looking there for them. And where your plants show up on the pH scale will determine how well they can absorb these all important nutrients.

Plants don’t have teeth, of course, but they do have roots and stems which serve as makeshift straws to uptake nutrients and minerals into their bodies where they can be used effectively. And that’s why water is so important.

Soil Nutrients and Solubility for Cannabis

Adding water or a soil solution to your soil eases the process by which nutrients and minerals are absorbed by plants.

The solubility of each nutrient is affected by pH levels with each having a different pH level at which they can be absorbed by a plant. For example, nitrogen can be absorbed at a minimum pH of 5.5 and a maximum of 7.5, while phosphorous can be absorbed at a minimum pH of 6.2 and a maximum pH of 7.2.

For optimum nutrient absorption, you’ll want the pH of the root zone for your soil-based marijuana plants to fall within a window of 6 to 7 on the pH scale.

Water gives nutrients a big assist in making their way into your plants, and it is important to strike the right balance between too little and too much. While a lack of water will cause your plants to wither and die, over-watering can be just as problematic as it can impair proper nutrient absorption.

Therefore, it is very important to understand just how much water your plants need.

Testing pH

While the pH of your soil is vital to the health of your plants, it should also be noted that the pH of the water or nutrient solution you use can alter the pH level of your soil. By testing and managing the pH of both the water and the soil in which your plants grow, you can help to ensure a healthy, well-performing crop.

Scientist holding a marijuana branch close up

There are two basic options for testing soil pH–digital pH meters or pens and pH measurement kits with drops. Pens are simple devices to use, requiring a basic calibration and inserting them into the medium (fertilizer, runoff and soil) to obtain a reading.

Measuring with drops requires a few more steps:

  1. Prepare and gently stir your fertilizer taking care not to over oxygenate it.
  2. Add the fertilizer to the test tube provided in your kit, filling it to the half way point, then adding three drops of testing liquid.
  3. Shake the test tube gently so the fertilizer and testing liquid are well mixed.
  4. Compare the color of your test tube mix to the color chart in the kit and adjust the pH accordingly.
  5. Follow the same process with your fertilizer runoff, and if it is off, also adjust the pH accordingly.

You can also use pH pens and test kits to test the water or nutrient solution.

Using a pH Adjuster

The pH adjustment products most commonly used by growers are bottles of PH Up and PH Down. These can be obtained at most any grow store and are available under various brand names. When using either solution:

  1. Add nutrients to your water bottle and then shake it to dissolve those nutrients.
  2. Test the pH level.
  3. If the pH level is too high or too low, add small increments of up or down solution to get the level where it needs to be.
  4. Test the pH level again and add more up or down solution if necessary. Once you get the reading you need, you can water your plants.
  5. Be sure to test the pH level of the runoff immediately.

Why Lower the pH Levels in Water?

Tap water, if you’re using it, is naturally slightly alkaline so adding a small amount of pH down solution helps to adjust it properly.

How to Adjust pH Levels

As discussed above, pH up and down-type solutions will do the trick, but there are options that provide the grower with a more hands off approach. The whole point of maintaining the correct pH window is to ensure your plants can absorb the necessary nutrients to grow healthy and produce a good yield.

Nutrient supplementation products like Advanced Nutrients Bloom, Micro & Grow provide a package of nutrients that assist plants through their entire growth process while also maintaining them at the perfect pH level.

Organic Ways to Adjust pH – For When There’s a Nutrient Problem!

The nice thing about growing plants in organic soil is that it is usually flush with tiny organisms that naturally break down nutrients and get them into your plants. However, going organic doesn’t always guarantee that your plants will “eat” right.

Nutrients are like potato chips for cannabis plants and, given the chance, they’ll gobble them all up quickly forcing you to add new soil or purchase supplements. Without the proper nutrients, especially in the flowering stage, you won’t get the yields you are looking for.

Farmer hands holds baby cannabis plant

As an organic grower, if you find your plants are experiencing nutrient lockout, that is, displaying nutrient deficiencies when you know your plants have not used up all the nutrients available in your soil, it is important to test the pH level of the water you are adding to your plants as well as that of the runoff.

If you find pH levels to be too high or too low, you can still correct the problem without abandoning organic growing practices.

Organic “pH Down”

Lemon juice and vinegar are two of the most common around-the-house natural items that can lower pH levels. Other natural products that will help lower the pH in your soil include manure, compost, worm castings, and compost teas.

Organic “pH Up”

Baking soda is often the household product of choice for raising pH levels. Lime and limestone in multiple forms is also commonly used. Wood ash will do the same job more gradually and will contribute a number of healthy micronutrients to your soil.


Is there a point in even buying pH up solution?

The main reason growers like inorganic pH up (or down) solutions is because they are easy to use. Just be aware they are sometimes known to kill beneficial bacteria which can set your plants back.

Is there anything I can use safely for a couple of waterings?

Foliar spraying is one way to address nutrient deficiency short term and quickly, particularly if applying secondary nutrients and micronutrients. Allowing plants to take in nutrients via their leaves instead of the root system avoids developing any nutrient build up in the soil.

Person planting industrial hemp in the soil

This method, however, should never be used to completely replace the intake process through the soil.

How do I manage the pH of my soil when growing organically?

Overly-alkaline soils can be adjusted to proper pH levels by adding tiny amounts of lemon juice or vinegar to your water. The solution should be mixed so that there is 5 to 10 parts of water.

The trick is to apply it slowly and gradually with continued regular testing until the pH level is where it needs to be. Some growers do the same with baking soda for overly acidic soils, but often the results are not long-lasting.

A better alternative with more lasting results is to add a liquid dolomite lime product to the soil.