Log in

Get your medical card online in minutes!

Get started

How to Monitor Water pH For Growing Cannabis Plants

closeup of water dews on cannabis leaf

The water pH for growing cannabis plants should always stay between 5.8 and 6.2. These values let your marijuana consume nutrients, grow strong, and produce heaps of sticky buds.

Marijuana is resilient in many respects, but it’s fussy about acidity and can only absorb minerals in a narrow pH range. Plant health and harvest potential suffer if the medium remains outside its preferred scope for too long.

Get Your Medical Card

Connect with a licensed physician online in minutes.

What Is pH?

Simply put, pH measures how acidic or alkaline a solution is. We express it on a 1-14 scale, where a value of 7.0 is neutral (pure water at 77°F). A substance is acidic when it’s under 7.0 (lemon juice and vinegar), while those over 7.0 are alkaline (soap, ammonia, and bleach).

In scientific terms, the abbreviation stands for the power of hydrogen and describes the concentration of hydrogen ions in a liquid. The value is inverse: the more molecules float in the liquid, the lower its pH.

The pH scale is logarithmic to the base of ten. As a result, slight number fluctuations make a significant difference in practice. To illustrate, water with 6.0 pH is ten times more acidic than that with 7.0.

Why is this chemical concept relevant for growing sticky buds?

In gardening, we discuss water, fertilizer, and soil pH. You grow plants in a medium and supply them with moisture and nutrients. These three factors work together to establish an environment for the roots and keep them thriving.

The Importance of Measuring pH

Growers measure the pH levels of their water, fertilizer, and medium because they affect plant health. Specifically, pH is the number one factor that determines nutrient availability.

Marijuana needs minerals to develop, and it draws them from the medium. If the roots can’t access food, the plant stops growing and may eventually wither and die.

When the environment is appropriately acidic, your cannabis gets the right amounts of all minerals and stays prolific. If there are pH problems, nutrient troubles soon follow:

  • Nutrient deficiencies result from the plant not absorbing enough food. The leaves usually lose color, curl inward, wilt, and fall off. The stalk, buds, and branches may also get affected.
  • Nutrient lockout happens when you supply enough minerals, but the plant can’t absorb them. It leads to a waste of valuable fertilizer and damages the soil.
  • Nutrient toxicity happens when plants consume excessive amounts of minerals due to overfertilization or pH issues. For instance, they absorb too much iron in very acidic soil. Their leaves curl, dry, and lose color.

You can avoid these problems by regularly measuring the pH. The earlier you catch an imbalance, the less likely it is to become a severe health issue.

The Best pH for Growing Cannabis

The best water pH for growing cannabis plants resides within a narrow window of 5.8-6.2 (most plants become unhappy when it’s above 6.5). Even then, we use ranges and not exact figures. Why is that so, and isn’t it better to always aim for the same number?

Marijuana needs minerals with varying chemical makeups, which become available at different pH values within its preferred window.

cannabis plant and a water dew on it's leaf

The pH fluctuates when you feed and water your weed, and you should let it. Slight changes let your plants consume everything they need, so don’t stress as long as it stays within range.

Once you master the basics of managing pH, you can tweak it for optimum nutrient uptake in each growth stage. Here’s the best pH for seedlings, vegging, and flowering plants:

  • Seedling stage: 5.6-5.9
  • Vegetative stage: 5.7-5.9
  • Early flowering: 6.0-6.2
  • Late flowering: 6.0-6.3

Managing the acidity for your weed depends on the setup. Let’s see how you do it in soil and hydroponic setups.

Download Our 7 Page Guide to Growing Cannabis

Soil Setups

Wild marijuana emerged in areas with slightly acidic soil, so it absorbs minerals best when the pH is 5.8-6.2. This medium forgives imbalances, and natural fluctuations support optimal nutrient uptake.

Loamy soils are acidic, offering a good base for cannabis plants. However, harsh chemical fertilizers may cause spikes and drops.

You face fewer pH problems in fully organic setups. When you use soil packed with organic materials, the microorganisms make nutrients more available to the roots. Deficiencies and lockouts happen infrequently.

Expert tip: If you’re not ready for compost and microbes, buy high-quality organic soluble fertilizer for weed. These products offer the convenience of chemical nutrients but cause fewer imbalances.

Hydroponic Setups

Plants in hydroponic systems thrive in more acidic environments. Their ideal pH is 5.5-6.5. This rule applies to all hydro cultivation systems, whether you use coco coir, Rockwool cubes, pebbles, or no substrate.

Considerable pH fluctuations are riskier in hydroponics. There’s no bacterial life to help the roots consume nutrients and no food except the one you supply. Stay mindful of your feeding schedule and acidity levels to keep your marijuana thriving.

How to Test and Monitor pH

A pH meter is a cannabis grower’s best friend. You should check the acidity weekly for preventative care. If you had previous issues, perform tests every time you feed and shower.

One pH reading is helpful, but three are even better for catching imbalances and knowing which element needs correcting. Grab your testing tool and check your:

  • Water source: This is especially important if you use tap water, as it’s often slightly alkaline in America. Let it sit and stabilize for a few minutes before measuring the pH.
  • Water-nutrient solution: Some fertilizers are very acidic and could balance the alkaline water. Again, let the blend sit for several minutes before testing it.
  • Runoff or reservoir water: If the prior two readings are appropriate and this one isn’t, your growing medium is the problem.

You can rely on these tools.

pH Drops

This straightforward test kit consists of a container, pH drops, and a color-coded chart.

Fill the tube with your water sample and add drops according to the manufacturer’s instructions. The liquid changes color, and you compare it to the chart to get a reading.

Since they employ ranges, drops aren’t the most accurate. They’re also tricky to use if your fertilizer stains the water; the liquid should be completely transparent before you add drops. Nevertheless, this option is inexpensive, accessible, and precise enough for most growers.

pH Strips

pH strips operate similarly to drops and resemble pregnancy tests. You get a container for the water sample, testing strips, and a color chart.

Fill the tube and dip the strip until it soaks in the liquid. Its tip changes color after several seconds, and you match it to the chart to get a rough pH measurement.

Like drops, strips are accurate enough for soil and some hydroponic gardens. They’re also cheap, easy to acquire, and straightforward to use.

pH Meters

Digital meters are highly accurate pH testing tools. They have electrode tips, which you dip in the water, and screens displaying the pH value.

These devices are precise, eliminating color charts and guesswork. They’re also effortless to use, displaying a reading in several seconds.

The two main downsides are the price and storage requirements. You buy a pen and two separate fluids for storage and calibration. One purchase sets you up for numerous growing seasons and ensures exceptional accuracy, though.

How to Adjust Water pH


What if you got a reading outside the ideal range? It’s time to correct the cannabis pH. Your actions depend on where the problem occurred.

If the substrate pH is inadequate, you must flush the medium first.

Flushing means treating a medium with pure water to release built-up salts and neutralize its pH. Here’s how to do it in soil:

  • Soak the medium with four times the container capacity of pH-neutral water. Pour slowly to avoid spilling, and let it drain.
  • Leave your pots in a warm and breezy spot for 1-2 days. Don’t water again until the top inch feels dry to the touch.
  • Shower your plants with a pH-optimized water-fertilizer blend and measure the runoff again.

Flushing a hydroponic tank is even more straightforward. Empty it, wipe its sides, and fill it with pH-neutral water. Let the liquid circulate for 24 hours before supplying a new dose of fertilizer.

How do you optimize the water or nutrient solution? Let’s see how to ensure the proper pH if you’re starting with one too high or low for marijuana.

Increasing pH Levels

Low pH results from soft water sources, like distilled water. A pH-Up solution is the quickest response. Add small amounts to the liquid, mix, wait a minute, and test again.

Expert tip: Write down how many drops you need to achieve the suitable pH. It’ll save you time and energy in the future.

Besides these adjusters, you can increase the pH with liquid dolomite lime or baking soda. The latter is more accessible but shorter-lived. Let either sit and dissolve for an hour before watering your plants.

Soil growers may also treat their medium with wood ash instead of correcting the water pH. This material fixes excessive acidity around the root zone.

Decreasing pH Levels

Given the values of American tap water, most growers deal with high pH. Store-bought pH-Down is the easiest fix. Add several drops to the liquid, stir, test, and check. Repeat till you reach the optimal amounts.

If looking for organic alternatives, small amounts of lemon juice and vinegar drive down pH. Pharmacies also stock several acids that do the trick.

  • Phosphoric acid: Found in fertilizers and store-bought pH-Down solutions. It’s low-cost and easy to find.
  • Sulfuric acid: This potent acidifier exists in batteries and acid rain. Use gloves and glasses while handling it.
  • Citric acid: Found in citrus fruits, cleaning agents, and nutritional supplements. It’s organic, cheap, and safe to handle.

Dilute tiny amounts of any acid in several gallons of water. They’re powerful and might damage the plant’s roots in higher concentrations.

The Bottom Line

Water quality and pH are among the critical aspects of successfully growing cannabis. Get them right to see your plants grow strong and nip numerous health issues in the bud.

Check the pH weekly for the best results. Maintain a 6.0-7.0 range in soil and 5.5-6.5 in hydro. Stock up on pH solutions or organic alternatives and adjust this figure as soon as you notice an imbalance.

Now that you understand this concept, you can produce top-tier buds at home. Visit our partner Homegrown Cannabis Co. to buy high-quality seeds and start your growing journey.

Get Your Medical Card

Connect with a licensed physician online in minutes.

diamond icon

Frequently Asked Questions

Should I pH my water before adding nutrients?

Add fertilizer to the water before testing and adjusting the pH. Most liquid nutrients are acidic, so the measure usually drops once you combine the two.

What are the signs of poor soil pH in plants?

Poor soil pH causes nutrient deficiencies in marijuana. Your plants appear weak, sick, and malnourished despite your regular and generous feeding schedule. The symptoms depend on which mineral is missing, but this problem usually manifests as:

  • Stunted growth
  • Red tinges on leaves
  • Brown spots on leaves
  • Purple stalks
  • Wilted leaves
  • Burnt leaf tips
  • Small new growth