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Nutrient Matters is a recurring series focusing on plant nutrition by university researchers. Learn how to germinate marijuana seeds on your FIRST try! Reach 100% seed germination rates by using our step-by-step tutorial. Marijuana pH and water For marijuana growers, whether using soil, soilless or hydro methods, pH levels can make a huge difference to your success and yields. In this article we will take a closer

New Research Results: Optimal pH for Cannabis

Nutrient Matters is a recurring series focusing on plant nutrition by university researchers.

The recommended substrate pH for cannabis (Cannabis sativa) varies widely. A recommended substrate pH of 6.0 to 6.5 often is cited as the standard. However, we have observed pH ranges between 4.0 and 5.0 or greater than 7.0 during our visits to commercial greenhouses growing cannabis.

Our observations from those greenhouses indicated that plants grown at acidic (lower) pH appear to have normal growth and lack the symptomology of lower leaf blackening or bronzing typically seen with other greenhouse species at lower pH levels. In crops grown at higher pH, only in rare instances did we observe interveinal chlorosis of the upper (youngest) leaves (a common symptom of greenhouse crops grown at high pH). These observations suggest that cannabis is not prone to iron deficiencies when the substrate pH nears 7.0.

Returning to our labs at North Carolina State University (NCSU), we began our work to understand the underlying factors affecting pH in substrates and how those fluctuations impact the Cannabis sativa plant in order to determine the optimal pH range for cannabis.

This is what we discovered.

pH on the Range

Substrate pH is important to plant nutrition because it directly impacts plant nutrient availability.

Substrate pH levels below 5.0 result in increased micronutrient availability that can lead to iron (Fe) toxicity or manganese (Mn) toxicity, or both. Symptoms of Fe toxicity and Mn toxicity may appear as black speckling on older leaves (observed with zinnias or gerbera) or as bronzing (observed with marigolds or seed geraniums). While some crops display low pH symptoms on lower leaves, others may only display low pH through stunted growth, as is the case with poinsettias.

In our initial experiments at NCSU, we did not observe symptomology of lower leaf blackening or bronzing on Cannabis sativa plants, only stunted growth. These preliminary results suggested that cannabis can regulate micronutrient uptake under low substrate pH conditions similar to a poinsettia.

When the substrate pH becomes too high, many species develop interveinal chlorosis (yellowing) on the youngest leaves. This is a common situation that occurs with many greenhouse-grown species (such as petunias) when the elevated pH makes micronutrients, such as Fe, unavailable to the plant, even if adequate levels are provided in the fertilizer.

We did not observe symptomology of interveinal chlorosis in cannabis plants grown at pH 7.0 in our initial experiments at NCSU, either. Iron uptake can also be hindered by over-irrigation, cold substrate temperatures or root disease such as Pythium. In other experiments at NCSU, we did observe the development of interveinal chlorosis on plants with a pH of 7.8. This observation provides more refinement of the upper pH limit and would suggest that the pH should be lower than 7.5.

The preliminary results of NCSU’s research imply that vegetative stock plants of cannabis have a wide substrate pH range in which the plants will optimally grow. That range appears to be as wide as pH 5.0 to 7.0. Based on experience with other species, a narrower range of 5.5 to 6.5 may be more appropriate to target, as this will allow growers to more easily adjust as pH approaches the ends of the targeted range.

For growers, utilizing these pH values in a monitoring system such as the PourThru method implies that the safe pH zone to target would be a narrower 5.8 to 6.2. If pH drops below 5.8 or above 6.2, corrective procedures should begin to adjust the pH back into the 5.8 to 6.2 range.

(Note: These values are for plants grown in greenhouse conditions with a soilless substrate (growing medium). Optimal ranges for field-based growing conditions typically would move up the lower and the upper range by 0.5 pH units to 6.2 to 6.7—as field soils latch on to more nutrients than a soilless substrate such as peat or coir, and risk of nutrient lock-up is lessened.)

How to Correct pH

Again, when the pH drifts into unwanted territory, adjustments must be made. Below are standard corrective procedures used to modify substrate pH for plants grown in soilless substrates in greenhouses and adapted for cannabis.

1. Low Substrate pH Correction When Fe toxicity and Mn toxicity become a problem, raise substrate pH to the recommended pH range. Corrective procedures to raise low pH levels are listed on p. 52 (Table 1). Switching to an alkaline fertilizer when substrate pH is nearing the lower limit will help stabilize the pH.

Flowable Lime

To make small adjustments of roughly 0.5 pH units, mix 1 to 2 quarts of flowable lime per 100 gallons of water. If using an injector, avoid using higher concentrations of flowable lime as it will damage it. If higher rates are needed, then split your applications to avoid damaging your injector. To avoid leaf burn, it is best to rinse the foliage after treatment if any flowable lime comes in contact with the leaves.

Hydrated Lime

For more stubborn low-pH problems, use a hydrated lime mixture. Mix 1 pound of hydrated lime in 3 to 5 gallons of warm water. Mix it twice and let it settle after each mixing. Once the sediment collects in the bottom of the container, pour the liquid through your injector system set at a 1:15 ratio. This product is corrosive, so rinse the foliage as soon as possible to avoid leaf burn, and avoid skin contact.

Potassium Bicarbonate (KHCO3)

Potassium bicarbonate should be handled with care. It can throw off your substrate chemistry as it provides 993 ppm of potassium (K) in mixtures of 2 pounds per 100 gallons of water. Rinse the foliage immediately after application via injectors and leach heavily the following day with a complete fertilizer to reduce substrate electrical conductivity (EC) and restore nutrient balance. The 2-pounds rate will increase the substrate pH by roughly 0.8 pH units. Rates greater than 2 pounds per 100 gallons of water can cause phytotoxicity.

As always, remember to recheck your substrate pH to determine if reapplications are needed.

2. High Substrate pH Correction The target pH for cannabis is between 5.8 and 6.2. Higher pH values may result in Fe deficiency and create interveinal chlorosis on upper leaves. Check the substrate pH to determine if it is too high. Be careful when lowering the substrate pH, as low pH can be more problematic and difficult to manage.

Cannabis plant growth is less vigorous at low substrate pH levels.

Acid-Based Fertilizer

If the substrate pH is beginning to increase, consider switching to an acidic-based fertilizer. These ammoniacal nitrogen (N)-based fertilizers are naturally acidic, and plant nitrogen uptake will help moderate the substrate pH over a week or two.

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Acid Water Drench

Some growers use this intermediate correction when pH levels are not excessively high and a quick lowering of substrate pH is desired. Sulfuric acid is recommended to acidify irrigation water to a pH 4.0 to 4.5. Apply this acid water as a substrate drench, providing 5 percent to 10 percent excessive leaching of the substrate. Rinse the foliage to avoid phytotoxicity. Results should be visible within five days. Retest the substrate pH and repeat if needed.

Iron Drench

If the levels are excessively high, then a Fe chelate application can be made to the substrate.

  • Iron-EDDHA can be mixed at a ratio of 5 ounces per 100 gallons of water.
  • Iron-DTPA can be mixed at a ratio of 5 ounces per 100 gallons of water.
  • Iron sulfate can be mixed at a ratio of 4 ounces to 8 ounces per 100 gallons of water.

Apply the iron as a substrate drench with enough volume to leach the pot, and rinse the foliage immediately after application.


Based on grower observations and initial experiments at NCSU, it is possible to grow cannabis with a wider soilless substrate pH range than most other species. Cannabis plants do not appear prone to develop leaf symptomology when substrate pH is too low or too high compared to the current general greenhouse standards—only plant stunting occurs at sub-optimal conditions.

Therefore, based on research and experience with other species, a wider range of 5.5 to 6.5 may be used. When adapting these values to a monitoring system, the recommended pH zone to target would be 5.8 to 6.2. By monitoring the substrate pH over time, one can assure that plants are within the optimal range.

Brian Whipker, Turner Smith and Paul Cockson are from Department of Horticultural Science, North Carolina State University, Raleigh, N.C. Hunter Landis is from North Carolina Dept. of Agriculture and Consumer Services, Raleigh, N.C.

How to Germinate Cannabis Seeds

An in-depth guide on how to germinate cannabis seeds. Discover different techniques on how to germinate marijuana seeds to ensure a successful cannabis crop.

Everything has a beginning.

Cannabis seeds, like all seeds, must undergo the germination process before it can grow into a weed-yielding beauty.

Countless cannabis germination guides litter the internet. However, none go as in-depth as our seed germination tutorial. Read along to learn how to germinate marijuana seeds like a pro.

You’ll discover everything you need to know about the art of germinating marijuana seeds. From the necessary equipment to different germination methods and everything in between, we’ve got you covered.

The Chemistry Behind Cannabis Seed Germination

Cannabis seeds require the right conditions to sprout.

Without the proper temperature, moisture level, or oxygen saturation, weed seeds will not germinate. Although you can readily germinate seeds outdoors, nothing beats controlled germination indoors.

Let’s take a look at the three primary elements that influence the germination rates of marijuana seeds.


Water is the key player in the process of germinating marijuana seeds.

The outer-layer of the cannabis seed acts as a protective casing that provides a two-fold defense — prevent damage to the inner embryo and prevent minimal moisture from premature germination.

However, if the marijuana seed is saturated with water, it will eventually absorb the moisture and kick-off the germination process.


Once the embryo activates through water saturation, it requires oxygen to jump-start the respiration process. Oxygen fuels respiration, which unlocks food stored within the embryo.


After the respiration process, the embryo consumes the food stores, which in turn produces energy. Energy is the necessary product that propels the germination stage onwards.


Even if cannabis seeds have access to water, oxygen, and energy, it’s all for nothing unless it has access to warmth.

As long as cannabis seeds experience 72-78°F during the initial germination process — they’ll burst forth from the ground and spread their primordial leaves under the sun or artificial light.

The three most important elements for successful weed seed germination

Why It’s Important to Germinate Weed Seeds Indoors

At its core, the germination process lays the foundation of cannabis plants.

Overall, marijuana plants will underperform without proper germination techniques compared to those that experienced ideal conditions during the germination process. Therefore, it’s always best to harness an indoor environment when germinating marijuana seeds.

What to Look For Before Germinating Marijuana Seeds

Before you begin the germination process, there are a few things you must look for.

Let’s take a brief look at each.

Damaged Marijuana Seeds

Ordering feminized or autoflowering cannabis seeds online is the best way to acquire top-shelf genetics.

The seeds, however, may experience a few bumps on the road during the shipping process. With this in mind, you must look over each seed to ensure there isn’t any damage.

As long as each weed seed is undamaged, the germination process will be smooth.

The Cannabis Seed’s Age

Next, it’s a good idea to write down the date on each seed pack once received.

By doing so, you’ll have a clear understanding of a seeds’ age. Like all things, cannabis seeds lose their luster as the years go by. Cannabis seeds may remain viable for decades. However, germination rates decrease over time.

Therefore, you should only germinate seeds that are properly stored for a maximum of 6-months.

The Cannabis Seeds Color

Lastly, you must check the cannabis seed’s color.

Cannabis seeds come in different sizes and exhibit various markings across the outer seed coat. However, the seed’s color is an excellent indicator that represents seed maturity.

In other words, light green to pale white seeds are immature and are likely unviable. Therefore, always make sure that your cannabis seeds are light to dark brown color before germination.

Take a close look at the seeds that you receive for damage or discoloration

Should You Use a Seedling Heat Mat?

Many new cannabis cultivators ask if they should incorporate a seedling heat mat into the equation.

Although seedling heat mats are excellent tools to ensure fast germination, they are not always necessary. Seedling heat mats work by producing a gentle warmth that won’t rapidly dry cannabis seeds during the germination process.

However, they may be overkill if you utilize them during hot days, such as those during the summer months. Alternatively, they are essential during colder months during the winter. Therefore, you can choose to harness a seedling heat mat based on the time of year that you choose to germinate marijuana seeds.

Three Easy Methods To Germinate Cannabis Seeds Indoors

Now that you have a broad understanding of germinating marijuana seeds let’s get some weed seeds poppin‘ with a few different step-by-step tutorials.

You’ll have a better idea of which germination technique to choose once you’re done reading this section.

1. How to Germinate Marijuana Seeds in Soil in Five Easy Steps

If you want to germinate weed seeds au natural — there’s no better option than using soil.

Here’s a list of what you’ll need to germinate cannabis seeds in soil:

  • Feminized or autoflowering cannabis seeds
  • Eco-friendly “starting” container
  • Soil
  • Water
  • Label
  • Heat mat (optional)

As you can see, the list above isn’t extensive in the least. In other words, germinating marijuana seeds in soil is incredibly affordable.

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Step One

First, fill an eco-friendly starting container with soil.

The golden rule? Don’t pack down the soil. Remember, the soil you choose must exhibit a loamy consistency. Hardpack soil does not allow proper water drainage and oxygen circulation, which, as you learned previously, are critical components for the seed germination process.

Furthermore, if you choose to use a heat mat, place the eco-friendly containers on top to warm the medium adequately.

Step Two

Label each container.

The last thing you want to do is forget what seed you placed into each container — especially if you’re germinating multiple cannabis strains at once.

Step Three

Now, it’s time to sow the cannabis seed.

Create a small hole that’s roughly 0.25-inches (6mm) deep. Gently place the seed inside the hole and cover it. It does not matter which direction you put the seed — believe us when we say that the seed and gravity will sort things out.

It’s important to note that each eco pot should contain a single cannabis seed.

Step Four

Gently pour a small amount of water into the area where you buried the cannabis seed.

At this point, you must ensure that the cannabis seed never dries out. Once the germination process begins — there’s no turning back. Therefore, allowing cannabis seeds to dry will guarantee inadequate germination or premature death.

Ultimately, you must monitor the soil and continuously apply water until the seed sprouts.

Step Five

The final step is patience.

The moment the seed is planted, most beginners ask: how long does it take to germinate cannabis seeds, or how can I germinate my seeds fast?

Healthy cannabis seeds typically break the surface within 2-4-days. Older seeds, however, may take upwards of 12-days to sprout.

The germination phase is an incredibly vulnerable moment for cannabis seeds. Therefore, Do notwe repeatdo not dig up the seed to “check on it.”

This is what you can expect after you successfully germinate your cannabis seeds in soil

2. How to Germinate Marijuana Seeds Using Paper Towels In Five Easy Steps

One of the most popular germination techniques is the paper towel method.

Here’s a list of what you’ll need for this low-budget method:

  • Feminized or autoflowering seeds
  • Dinner plate
  • Paper towels
  • Spray bottle
  • Labels
  • Heat mat (optional)

Now that you’ve gathered the necessary supplies let’s get crackin‘.

Step One

Place two to three sheets of paper towels on top of a clean dinner plate. If you decide to use a heat mat to increase the temperature, place it under the dinner plate.

Step Two

Label the dinner plate with the name of the cannabis strain of choice.

Step Three

Place up to 10-seeds per plate.

You must make sure that a minimum of 1-inch adequately separates the seeds.

Step Four

Spray water on the seeds until the paper towels are completely saturated. Once done, place a new layer of 2-3 paper towel sheets on top of the seeds. Use the spray bottle to soak the new paper towel addition.

Remember: the paper towels must always remain saturated with water. If allowed to dry, the cannabis seeds will fail to germinate.

Step Five

The germination process should occur within 24-48-hours. After 48-hours, gently peel back the upper paper towel section. If the seeds germinate, you will see cracked-open seeds with an emerging radicle.

At this point, it’s time to move the germinated seed to its new home with a pair of tweezers. This final step requires extreme care because the radicle is fragile, and if broken, the embryo within will die.

Be careful when you use the paper towel method and make sure to label each plate

3. How to Germinate Marijuana Seeds Using Rooting Cubes in Five Easy Steps

Germinating weed seeds with rooting cubes is the ideal method for beginners and professionals alike.

Overall, rooting cubes provide the ease of the paper towel method and the soil technique’s efficiency. Let’s take a look at everything you need to when germinating marijuana seeds with rooting cubes.

  • Feminized or autoflowering seeds
  • Rooting cubes
  • pH 6.0 water
  • Rooting tray
  • Labels
  • pH meter and pH up or down
  • Heat mat (optional)
Step One

First and foremost, place the rooting cubes in the rooting tray. If you decide to use a heat mat, place the tray on top.

Step Two

Next, label each rooting cube or tray with the appropriate name of each cannabis strain.

Step Three

Use a pH meter and pH solution to achieve a pH of 6.0.

The amount of water you pH depends on the number of rooting cubes. Start with one cup of water if you are germinating less than ten seeds.

Germination cubes require a pH of 6.0 because they are typically made from peat moss, rockwool, or other soilless-based mediums. Therefore, a pH of 6.0 will ensure the best possible results once the seed germinates.

Step Four

Each rooting cube is equipped with a pre-made hole.

Place one cannabis seed per hole. You may tear off a small piece of the substrate to cover the opening. Once done, saturate the rooting cube with pH 6.0 water.

You must make sure that the rooting cube never dries out. Remember, cannabis seeds must remain moist until they sprout to the surface.

Step Five

Once again, patience is the final step when you learn how to germinate cannabis seeds with rooting cubes. Overall, cannabis seeds may emerge from the rooting cube within 2-4-days. However, germination may take as long as 7-days.

There are a lot of rooting cubes to choose from, but the germination process remains the same

How to Germinate Old Cannabis Seeds

Now that you understand how to germinate healthy cannabis seeds let’s quickly discover how to germinate old marijuana seeds.

As you become infatuated with the world of cannabis, you’ll soon begin to stack an extensive seed collection. Don’t worry; we’re all seed hoarders at heart because there are so many incredible cannabis genetics out there.

Eventually, however, you’ll notice that you have more than a few old cannabis seeds. Luckily for you — all is not lost.

Here’s our tried and true technique to give your old seeds a boost during the germination process.

Cannabis Seed Scarification

Scarring cannabis seeds is incredibly simple.

All you need is a nail file or a piece of sandpaper. Use the file or sandpaper across the surface of the seed in question. You do not need to use an immense amount of force, but instead, a few good scrapes to scar the seed’s outer shell will do.

The point of seed scarification is to allow water to penetrate the seed coating easily. By doing so, the embryo receives a jump start that initiates the germination process.

Once the seeds are scarred, you may choose one of the three above mentioned techniques to complete the germination process.

A few readily available tools to get your cannabis seed scarification done

The Best Way To Germinate Marijuana Seeds

Now that you’re done reading this guide on seed germination — which method will you choose?

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The soil, paper towel, and rooting cube methods are all tried-and-true and provide excellent germination rates. Remember, cannabis seeds are an investment, and you must use the best germination method possible to ensure a healthy cannabis crop.

You have one chance to germinate each seed the right way, and by using this guide, you’ll make each seed count.

Marijuana pH and water

For marijuana growers, whether using soil, soilless or hydro methods, pH levels can make a huge difference to your success and yields. In this article we will take a closer look at pH values and discuss why you need to know about them and how that knowledge can help you become a better grower.

What is pH?

So, let’s start at the beginning. pH is the measure of the acidity or alkalinity of a given substance. Technically it is about the concentration of hydrogen ions. A pH of 7.0 is totally neutral, 1.0 to 6.9 is acidic and 7.1 to 14.0 is alkaline. When using a pH scale it is important to know that the decimal points really count. The pH scale is a logarithmic scale which means that for every one point of pH, the concentration changes by a factor of ten. For example, an increase in pH from 7.0 to 8.0 is actually a tenfold increase, so be aware!

Why is pH Important in Growing marijuana?

  • The optimum pH for marijuana in soil is around 6.3 – 6.8
  • The optimum pH for marijuana in soilless or hydro is around 5.5 – 6.1

pH in Soil

When growing marijuana in soil you are less likely to run into pH problems, especially if you are using especially mixed soils that feed the plant throughout its life, without having to add any liquid nutrients. It is said that the soil acts as a buffer, this means that it helps slow the change of pH values as opposed to hydro systems where changes in pH take effect much more quickly.

  • The same thing happens when you grow marijuana in soil in containers. When you add water the pH of the soil changes and the whole range of nutrients become available to your plant as the soil slowly dries out again;
  • This means that some nutrients that are otherwise dormant in the soil become available when it is wet.
  • If you are using tapwater, make sure you let it sit in a bucket or reservoir for a few days to allow it to dechlorinate. Then check the pH to make sure it is within your required range.

pH in Hydro

If you grow marijuana in a hydroponics system then pH management is a much more important issue. With no soil to act as a buffer changes in your pH values take effect much more quickly. With hydro grows allowing your pH to fluctuate within a prescribed range is important as it allows all of the nutrients in the solution to become available to the plant in turn. Luckily, this happens naturally as the pH of the solution in your hydroponic reservoir will drift over time. When making up the nutrient solution for your hydro set up, always mix the separate components in the water. Never mix them together directly. This can cause them to chemically react with each other and may change their desired properties. Mix your nutrients gently. Overly vigorous mixing adds oxygen to the solution and this will temporarily raise pH levels. Some growers like to shake their solution vigorously to add oxygen which is good for the roots. If you like to do this, do it after you have checked and adjusted the pH. Make your mix in a clean reservoir and check the pH. Let the mix stand for an hour and check the pH again. The pH of nutrient solutions often changes quite quicklywithin the first hour so you should recheck and adjust as necessary.

Making adjustments to pH

If you are topping up your solution, or adjusting the pH in your reservoir, try not to subject the plants to drastic changes in pH. Large swings in pH will stress them. Make changes slowly. Do not mix nutrients or pH regulators directly into the plants’ reservoir. Make a mix in a separate container first then add that to your reservoir so that changes take place slowly. Remember that pH drift is not only normal, it’s desirable. Allow the pH in your reservoir to change gradually, but make sure you keep within the range of 5.5 to 6.5.

Checking pH

Although many soil growers don’t bother, a pH tester is a crucial piece of kit for the serious marijuana grower. There are a couple of options that are available to you. Digital Meter – This is by far the easiest, most popular and most accurate method for checking your pH levels. Digital pH meters are easy to work, just insert the probe and read the pH levels off of the digital read out. pH Strips – Cheaper to buy initially, but more expensive in the long run, and more hassle. pH strips turn a specific color depending on the pH. You then compare the color to an index and that gives you the pH value. If you are trying to measure the pH of your soil you will need to make up a soil solution in water. You should measure pH periodically as part of your plant maintenance program. With experience you will need to measure less often as you get your set up dialled in. Special care should be taken to measure pH when you seriously change the nutrient regime you are following, when flipping to 12/12 for example.

Adjusting pH

So, having checked the pH levels of your nutrient solution you find that it is out. How do you adjust it? The best answer is to buy proprietary pH Up and pH Down solutions. There are lots of forum posts by people who add vinegar or baking powder to adjust pH. Whilst there is some convincing evidence of this working, we recommend using proprietary solutions for reliable results.

pH Up is a strong alkali formula for raising pH. The one from General Hydroponics is made from a base of Potassium Hydroxide and Potassium Carbonate.

pH Down is an acid based formula for lowering pH. General Hydroponics up/down is made from a base of Phosphoric Acid.

As explained above, adjust the pH of your solution a little at a time. Try to use only either Up or Down. If you overshoot with one and then have to readjust with the other you can end up unnecessarily stressing your plants. Mix up a little of the required pH adjuster in a separate jug. Then add them a little at a time to your reservoir. Allow time for the whole reservoir to even out and settle. Better to get it right with 3 slight adjustments than have it wildly swinging up and down.

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