Best PH and TDS/EC Levels For Cannabis Plants

All living things on earth need water (H2O) to survive. Plants (just like humans) require water and are made up of about 2/3 water. It’s important to have a good understanding of the type of water that your plants receive in the same way that it’s important to know how different foods have different effects on our own bodies. Water content is always different, so we’ve provided a few guidelines to understand how it’s used.

pH scale

The pH scale essentially measures the acidity and alkalinity levels in water. “pH” is an acronym for the potential (p) of the existence of the hydrogen ion (H+) in the water. The scale runs from 1 to 14, meaning that a pH of 7.0 has an equal balance between hydrogen ions (H+) and hydroxyl ions (OH-).

Use water with pH 5.8 for marijuana
Use water with pH 5.8

You can think of pH like the hotness or coldness of your food. If your food is too hot, then you will burn your tongue or get heartburn. If it’s too cold, your teeth will hurt and you’ll get brain freeze. Finding the ideal pH balance is important for marijuana plants to absorb their food and have good health.

Download my free marijuana grow guide and find out more about how to keep pH and TDS levels well in control.

The plant may experience conditions throughout the scale that affect its ability to absorb certain nutrients. That’s why it’s very important to monitor the pH levels in the soil and the water so the roots and the plant itself remain healthy.

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Soil, hydroponics and aeroponics

The medium of soil acts as a buffer that can mitigate damage from any mistakes. That is to say, soil is much more forgiving for newbies. Of course, any damage that occurs with soil is much more difficult to fix. To avoid poor pH levels, mix a sample of your soil with distilled water, and then test the pH level of the water.

Hydroponic systems function by feeding all the nutrients a plant needs through mediums that are rather inert compared to soil. This effectively reduces the buffer zone that soil provides. Cocos or rock-wool can still provide a small buffer that contains its own pH level. Of course, you should compensate for that by adjusting the nutrient solution.

Hydro vs soil method of growing weed
Hydro vs Soil

With aeroponics, there is no medium, which means there is no buffer. You won’t have to compensate for any medium so the nutrient solution in the water can be input directly.

It should be noted that the pH level of a nutrient solution is not always the same as the pH level at the plants’ roots. Look at the table to find compensation values for different mediums. pH, TDS/EC values are often contingent on temperature and time.

The primary food delivery system is water, and the plants use a process called “osmosis” to make it happen. The plants pull in nutrients through their roots and the nutrient levels are balanced in the water that’s in the plant and the water that’s around the roots. All the nutrients are absorbed through the external water, and the plant discharges waste (salts). Plants use the same “don’t-shit-where-you-eat” logic that we do, meaning that it’s important to understand how many and what nutrients are in the water.

TDS and EC

Inexpensive pH meters can be found at most garden centers, grow shops, and pond stores. You can measure the concentration of ionic salts in the water with two different scales:

  • Total Dissolved Solids (TDS) measured in  Parts Per Million (PPM)
  • Electrical Conductivity (EC)

Water that is pure H2O will not efficiently conduct electricity, but most tap water will contain necessary ions (H+ and Cl-) for conducting electricity. More ions will result in better conductivity. We use this relationship to determine how many nutrients (salts) are in the water.

Plants require diets that are as diverse as diets for people. Some plants may need larger meals that offer more nutrients for growing. By contrast, other plants might be “drowned” by too many nutrients and would require smaller meals. The best TDS values will differ depending on the foods provided and the plants themselves.

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Feeding the plants

Soil For the most part, the pH balance is more important to soil growers than TDS/EC values (although an TDS meter is always a good investment). You can monitor the soil using only pH and staying within the recommended range.

That being said, some nutrients are absorbed more fluidly at different pH levels. The graph illustrates the ideal pH values to optimize nutrient absorption. For instance, nitrogen (N) absorbs better at pH 6.0, while phosphorous (P) and potassium (K) are better at 6.25 and up. This may necessitate a change in pH values when you shift from vegetative state to flowering.

Quick Tip: Always prepare the formula before measuring and changing the pH when you’re mixing a nutrient solution.

Hydro-, Aero- Because hydro- and aero- mediums limit the effect of the buffer, it’s important to focus on TDS/EC, and pH. Nutrients can be absorbed more easily at different TDS values. Hydro- and aero- mediums use direct feeding, which means that you have to carefully ensure that the plants won’t starve while also making sure that they don’t receive too many nutrients which can restrict absorption.

EC Meter for water checking
EC Meter

If you’re using reservoir or re-circulatory water systems, then certain cleansing methods like reverse osmosis can drastically improve water quality. It effectively filters out surplus salt build-ups, ensuring that growers will be able to maintain their water quality and support the absorption of nutrients. All of this is sure to provide maximized results.

In the end, making sure that your water quality is high requires some work, but it’s important to achieve a successful product. Next week I’ll upload some example feeding schedules and show you how to mix and level your water. Download my free grow guide and order some high quality marijuana seeds at this link here. We ship seeds to the US, CA and many other countries.

For any growing related question please visit the marijuana support page.


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Robert Bergman


Robert Bergman is an Amsterdam-based marijuana grow expert who has years of experience from small grows to massive operations ... See profile

39 comments on “Best PH and TDS/EC Levels For Cannabis Plants”

  1. I do a lot of nutreint maping and most nuts when following schule will end up very acidic.I know what most of my nuts do in the water.L believe you should write an article about this as alot of people I know think if the water they use is ok then they believe it,s ok.wrong.I use drops instead of my meter,fast and accurate.

    • Hey chink,

      Your comment is a bit unclear. I would like to say that I do not believe that most soluble nutrients range acidic. First we will start with the water. ultimately the water is going to determine the final PH of any solution mix. If you have high PH water or alkaline water above 7.0, then you will end up with a PH that has to be adjusted down. Low PH or acidic water will possibly remain in the proper range once mixed with water soluble nutrients or minerals (as I do in the greenhouse).

      Thanks for your comments.

  2. PPM is defined as Parts Per Million of (Something) dissolved in the liquid you are measuring.
    Unless you have access to a gas chromatograph in order to measure what exactly is making up your PPM, then the best measure is to rely on pH for proper nutrient uptake. See the previous posts here for the proper hydro or soil pH (5.5 -65.) Measure the pH of your nutrients (add the x tsp/gal and then check the pH) and adjust. Then water and check the runoff pH and readjust as necessary.
    It’s a balancing act…

  3. What’s the relationship between PPM and the feeding schedule provided by the nutrient manufacturer? I’ve used the Fox Farms “main 3” lineup for my first 3 plants and have followed their schedule (starting at quarter strength), but I’m curious if I should ignore the dosages in the feeding schedule and rely solely on PPM instead?

    • Dan,

      You can do it wither way. I teach some growers to use the directions on the bottle because a multi-million dollar company did the research and advised you to follow their feeding schedule (sometimes different than guidelines on the bottle).

      On the other hand I also teach the ppm method of using less and building ppm strength as the plant gets bigger and then as flower develops. You can use 400-600 for seedling bumping to 800-1000 in late veg, and then run 1000-1200 during flowering with a boost of Potassium (K) 2-4 week before estimated harvest date.

      Hope this helps, 🙂

  4. I’ve been researching urine as a fertilizer for plants, this might sound gross but I’ve been drinking a diluted urine solution to help my HEP C. Would adding a diluted urine solution to my plants help them grow?

    Aaron Keith O’Brien

    • Aaron Keith O’Brien,

      Personally, I would not use as urine solution unless it was a last resort. If you already have a nutrient regimen, merely adding urine is not going to give you much of an advantage in the long run. Might be useful in an “off grid” situation or if you run out of nutrients but, in general it is OK but, not recommended in general.

      Happy growing

  5. My water comes out of the well at around 427 ppm. Is that a problem? If so, what should i do about it? ( if it matters, i plan to grow hydro/bubbleponics)

    • Dan first thing is to filter your well water to lighten the PPM then replace said PPM with nutrients based PPM however you filter it is your call but at 427 theres no room for anything else for your babies other than the calcium and iron from the well. I might advise a whole house filter and then a finer micron filter for your plants water.

    • Dan, Sorry wee missed this but, for future reference. If your ppm of tap water is 427; I would invest in a small Reverse-Osmosis unit 4-5 stage approx. 100 bucks on e sites.

      Happy growing

  6. Different nutrients break down at different PH levels. With that said, can you fluctuate your PH from 5.5 to 6.8 through out its cycle in order to break down the right nutrients at the right stage when using hydroponics?

    Please advise, Thank You!

    • jack kirkendall,

      Different minerals are more available in certain PH levels. They are all available at proven pH of 5. for Hydroponic grows, and 6.5 in Soil grows.

      NO you cannot and should not fluctuate your PH from 5.5-6.8 unless you want to lock out some minerals causing issues with your plants.

      You need a consistent PH in order for the plants to use their energy to thrive.

  7. Denny,
    nuts = mutes; I suppose. It is best not to abbreviate when asking for grow advice.

    1. It is not advisable to add nutrients to new plants in Sunshine soil. Nutrients should be held back until the transition/flower phase of the grow.

    2. You could be over watering because, there is no scdeule to water soil, other than when the plant medium is dry. By watering small plants every other day; You may be drowning the roots.

    3. Optimum PH for soil grows is 6.5

    Between the 3 it is hard to diagnose your issue because, both mistakes can cause leavers to yellow. This is where I would start looking, though.

  8. I Started out with very few Nuts in sunshine # 4 soilless mix and plants were about 8″ tall total green and then started to turn a little yellow a few leafs. I was watering every other day with 5.8 pH led lights about a foot above the plants Humboldt–micro, Grow , bloom mix. After seeing the yellow leafs I increased the nuts at around 600 then cut back to 450 PPM total including the well water. It looked like burn yellow leaves brown tips curling up and down.? I checked my well water and it says 258 PPMs so I went to plain 5.9 pH well water. Everything is still the same. Then I cut the nuts in half. Still the same. Now I’m back on plain well water pH 5.9 still the same. This is over a month or so and I can’t figure it out. The plants are mostly yellow I now ordered an osmosis system thinking maybe it’s the well water? Anyone have any other thoughts? Thanks Denny

  9. Nutrients are in all food, and available to all living beings. Life and photo synthesis cannot occur without proper nutrition.

  10. This article treats nutrients like they are a food source and that is not true. One does not want to think of fertilizers as food. Plants are Autotrophic meaning they make their own food. The fertilizers are more like vitamins. Too much and you will hurt the plant.

  11. For hydro, Ph range goes from 5.5 to 6.5… so 5.9 or 6.0 is the goal for the whole cycle.
    650 PPM in first vegettive week , increasing by 50 every 7 days.

      • Jack. You can go that high a nutrient concentration. You will never get the chemical, or fertilizer taste out of the plant. 1000-1500 ppm is all you need to grow really nice tasty plants.

  12. 150 ppm is a very light nutrient solution. Joining the support forum and asking questions will get you the opportunity to access much more info. I look forward to helping you out there. lw

  13. 20 ppm is great for watering your plants. 🙂 Have you go a nutrient schedule planned for your plants? Perhaps it would be great, if you joined the Support forum.

  14. Hi. Help needed.
    I have young seedlings in a hydro system. What are the recommended ppm levels?
    Any info will be highly appreciated.

      • If starting out @ 500 ppm having only 4 wk. of grow & 4 wk. of flowering using auto-flower with hydroponics whats’ the max?

        Also, if using EC not ppm what numbers are used?

        TX Jack

  15. This is the absolute most important information you need to understand to grow healthy plant over and over again. Knowing how to read and adjust the PH of your plants is imperative.

    When it come to EC/PPM; It is very important to know that sometimes, “less is more”. Don’t over0fert your plants because you are impatient and want to see them get bigger over night. Learn how to measure your run off in soil, or your res PH in hydro. Get ahead of the game.

    Happy growing