The role of pH in cannabis seed germination

Potential hydrogen or pH is a scale used to measure acidity and alkalinity in objects. Growers use it to measure the soil and water they provide for their cannabis plants. PH plays an important role in soil quality and contributes to a plant’s water and nutrient uptake(1).

The importance of pH isn’t limited to established cannabis plants. It is also crucial even in the early stages of germination. You might argue that since seeds have food reserves, they won’t need as many nutrients. But, that reserve is actually exhausted once the seedling has emerged and begun growing its roots and leaves. By that point, you will need to start providing the necessary water, nutrients, and light for your seedlings(2).

Does pH matter when germinating cannabis seeds?

Measuring the pH value of the water you’re using to soak your seeds is important. Doing so helps avoid creating an unfavorable growing environment for your newly germinated seeds. Like temperature, water, oxygen, and light, pH is critical in ensuring a comfortable growing environment for germination.

A study in 2006 has also shown that high pH levels negatively affect the germination rate of seeds. Do note that germination rate and germination percentage are two different things. Germination percentage refers to the potential of a seed to sprout. On the other hand, the germination rate is the speed at which a seed develops and takes root.

In my free Grow Bible you will find even more tips for sprouting seeds and how to germinate weed seeds properly!

Can pH negatively affect cannabis seed germination?

Yes, it can. Extreme pH levels will slow down the germination rate of seeds due to nutritional stress. This happens due to trace nutrient deficiencies from alkaline soils or major nutrient deficiencies from acidic soils. To avoid this, keep your pH levels within the benchmark range for germinating cannabis seeds.

What is the best pH range for cannabis seed germination?

The ideal pH for germinating your cannabis is around 5.5-7.0. Within this range, both trace and major nutrients can be absorbed by cannabis(4).

What pH is good for seedlings?

As seedlings, your cannabis’ top priority is to generate food for itself to grow, which they do through photosynthesis. But that’s only possible if there’s enough nitrogen and magnesium in the soil to make chlorophyll, which your plants can only absorb if the soil has a pH level of around 6.0-7.0.

Ideal pH ranges for your growing medium at each stage of cannabis plant development

Growth stage cannabis plant pH range
Germination 5.5 – 6.5
Seedling6.0 – 7.0
Vegetative6.0 – 7.0
Flowering6.5 – 7.5

Optimal pH for Osmosis

When watering cannabis, use water with a pH level of around 5.5-7.0. Anything lower than 5.5 will affect the water uptake or osmosis of your cannabis (5). Additionally, low pH doesn’t just affect water uptake but also overall water activity in plants. In fact, a 2017 study claims that low pH caused a decrease in both water flow rate and hydraulic conductivity in the roots of seedlings. That essentially means that the plants had slower water uptake in substrates with low pH.

Besides pH, other important factors affect plants’ osmosis. The main ones are salinity and temperature. Temperature matters because it’s tied to transpiration, which your plant needs as part of the vacuum cycle that provides force to transport water and nutrients from the roots to the rest of the plant. 

As for salinity, it’s different from pH in that it measures salts in the soil and water(7).  However, it’s equally, if not more, important than pH since it has a greater effect on osmosis. This is because high salinity in soil water can cause the water inside the plant to flow back into the soil(8).

Checkout our ultimate guide on: How to measure pH and PPM for your marijuana grow!

How do you gauge/check the pH range of the water used when germinating cannabis seeds?

A pH meter is one of the most commonly used instruments for measuring alkalinity and acidity in water and other solutions. It measures the degree of hydrogen ion activity (potential hydrogen) in the water, which generally ranges from 1-14. 7 being neutral, >7 being basic(alkaline), and <7 being acidic.

Table of acidic and alkaline solutions that can be used to get high yields from marijuana plants

Typically, growers pair a pH meter with a TDS meter. A TDS or Total Dissolved Solids meter is an instrument used to indicate the total amount of dissolved solids in a solution (in our case, water). The solids here refer to the minerals in the solution (i.e., iron, magnesium, and calcium salts). TDS levels will tell you whether the water you’re about to use for germinating your cannabis seeds is ideal for them or not.

A PH meter showing ph values for the soil and water

How do you adjust the pH range of the water used when germinating cannabis seeds?

You can adjust the pH of the water you use for germinating cannabis by adding substances that will make it more alkaline or acidic. Products like baking soda and lye will make the water more alkaline. On the other hand, things like lemon juice or vinegar will make the water more acidic.

Also learn, what’s the best pH and EC values for hydro marijuana growers if you want a more in depth view at the best pH levels for all types of cannabis seeds!

What causes poor germination?

Overwatering, lighting, and extreme temperature are some factors for poor seed germination. With overwatering, you may drown your seeds if you leave them out to soak for more than 24 hours. But giving too little is also an issue. If you don’t give your seeds enough water, it won’t trigger the seed’s chlorophyll to begin photosynthesis, resulting in a slower germination process

Another factor that affects the rate of germination is light. You should provide 16 hours of light and 8 hours of darkness for your seeds. Too little of it will slow down the rate of germination, but too much light will cause light stress in your seedlings. And then there’s temperature. Maintaining a temp of 72°F for your seeds(22°C) is important. Too cold, and your seeds will not germinate. Too hot will cause heat stress on your newly germinated seeds.

Lastly, pH. Besides contributing to the germination percentage of your cannabis seeds, it also plays a role in establishing your seeds. The ideal pH level for your substrate should be between 5.5-7.0. If your substrate is wildly on one side, it can create an unfavorable environment.

It is important to note that even if you follow all of the instructions in our Weed Grow Bible to the letter, some of your seeds will still not germinate. It could be because they’re old seeds or have bad genetics. If you want to avoid that, purchase high-quality seeds at ILGM – where every seed is guaranteed to germinate.

Know how to perfectly time your harvest so you can maximize your yield. Download our free mini harvesting guide!

Sources and Citations

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Mr Chris Gardner

Botanist and academic

Chris Gardner is a botany buff with years of experience in agriculture and graduated with a Bachelor’s degree in Science an ... See profile

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