pH and PPM: Knowing What Your Plants Are Eating and How Much They Can Handle

pH and PPM: Knowing What Your Plants Are Eating and How Much They Can Handle

One big question growers ask is “Why are my plants suffering even though I used all the right nutrients, feeding cycles, my grow lights are good, and I adjusted temperatures & conditions to their absolute best?”

Related: Growing Marijuana Indoors Guide 2018

That’s because their pH and PPM levels are off, making it difficult for your plants to eat. pH refers to the potential of Hydrogen ions in your water, which will determine if your water is too acidic or has too much alkaline in it. PPM (parts per million) refers to the concentration of minerals and soluble matter in your watering solution.

Correct pH and PPM levels are the backbone of any grow room and will be the difference between a healthy harvest and a huge waste of time and money.

pH Levels

Simply put: the right pH level will create an environment where your plants can absorb nutrients quickly and easily, leading to a better harvest.

Nutrient-rich water is filled with elements that are helpful to your plants. However, if those elements can be broken down properly those same elements can harm your plants.

pH levels are important to understand because the right level will determine the quality of helpful bacteria in your water that help break down elements, helping the metabolic rate of your plants. How? In two ways:

  • When pH levels are too low (pH level of around 5 or lower), heavy metals like iron and aluminum change and can become toxic to your plants
  • If the pH level is too high (pH level of around 6.5 or higher) elements like calcium and phosphorus can’t be broken down completely, which will hinder the growth of your plants

This change in properties is due to how acidic your water is or is not. You’ll want your plants’ nutrients to be a little acidic otherwise they can’t break down, but too much acidity and your nutrients can become toxic.

So Remember: pH too low= toxic to your plants, too high= growth decrease. That’s why you want to have the perfect level of acidity in your water, which will be around 5.5-6.0

Typical pH Levels 

  • 3.5 and below: Root Damage
  • 4.0-4.5: Poor Nutrient Uptake
  • 5.0-5.4: Good pH Level
  • 5.4-5.8: Perfect pH Level
  • 6.0-7.0: Acceptable pH Balance
  • 7.5-8.0: Poor Nutrient Uptake
  • 8.5 and Above: Root Damage

Note: Soil-grown plants tend to need a little bit higher of a pH than hydroponics because soil retains and releases certain elements to your plants at different times. However, both hydroponic and soil pH levels should stay within the same optimal range of 5.5-6.0 pH.

PPM Levels

PPM (Parts Per Million) refers to the concentration of the particulates in your feeding solution.

From minerals found in tap water to natural elements found in your nutrients, your job is to make sure that the PPM levels in your watering solution are on point so you’re not under- or over-feeding your plants. While it’s an easy concept to understand on the surface, it’s a little more complicated when you have to adjust nutrient elements inside your grow room or grow tent.

Now, pH plays a huge factor in PPM levels because even though you may have the correct PPM reading, some of the particles- and the concentration of those particles- can be harmful to your plants.

For example, let’s say your plants need to be at a PPM level of 700. You mix your solution and you get a PPM reading of 700 but your pH is around 4.5. That means that the majority of the available food for your plants is likely to have lots of heavy metals in it, which will quickly toxify the plant. You’ll need to adjust the pH level of your solution to make sure you’re not toxifying your plants.

“But won’t that throw my PPM levels off because you’re adding particles to your feeding solution?” It can, and that’s what’s so tricky about PPM and pH levels: When you adjust one you usually have to adjust the other, which can be simple or a huge pain depending on the water and nutrients you’re feeding your plants.

Common PPM Readings

These readings reflect the PPM your water should have at a given stage of growth

  • Seedlings: 100-250 (nutrients aren’t really needed here, hence there’s not a lot of particles needed)
  • First Half of Vegging Cycle: 300-400 (this is usually after you transplant, which still doesn’t require many nutrients)
  • Second Half of Vegging: 450-700 (you’ll start giving your plants more nutrients at this stage)
  • First Half of Flowering: 750-950 (your plants will be eating more as they grow, so they’ll be taking in more nutrients)
  • Second Half of Flowering: 1000-1600 (this is when your plant’s eating the most, especially if you give it additives)
  • End of Flower, Entering Harvest: As close to 0 as possible (this is when you’ll be flushing your plants, so you don’t want there to be a lot of particles left over)

Adjusting pH Levels

When it comes to feeding plants there are two ways of looking at it: homemade or store bought.

Same goes with balancing your pH: you can either purchase a pH buffer from a store or you can use ingredients you can find around your home or in the grocery store– but both come with their advantages and disadvantages.

Homemade pH Buffers

  • Advantage: If pH levels are high you can use a little citric acid or even white vinegar to help bring your water’s pH down. When your pH levels are low you can use a little bit of baking soda in your solution and bring those readings back up. This will cost you less than picking up a buffering solution.
  • Disadvantage: The issue with using these solutions is that they don’t work for very long. You’ll find yourself having to add a little lemon juice every other day, then having to use a little baking soda to even things out. Moreover, we’ve also heard of growers using these ingredients and seeing severe spikes in pH, which if not handled properly and quickly and bring plant growth to a halt.

Premade pH Buffers

  • Advantage: Most hydroponic companies out there will have pH buffers, usually called pH Up & pH Down. They’re much easier to use than citric acid or white vinegar mixes. They’re designed to raise and lower the pH of your water while keeping your water’s pH levels balanced for longer than it would be without them.
  • Disadvantage: As we’ve always mentioned, easier usually means more expensive. These solutions usually won’t cost you an arm and a leg, but they’re definitely something you can’t simply make at home and will cost some money.

Be sure to check your pH levels because no matter how much you train your plants- like FIM’ing or using the Sea of Green method if your pH levels are left unchecked they will bring plant growth to a halt!

Adjusting PPM Levels

Before you start adjusting your PPM levels, you’ll first want to make sure your tap water is ready to feed your plants. That means you’ll want to adjust the PPM of your base water before you start feeding it to your plants.

Now, any time you add anything into your watering solution, you’ll be adding more particles into it, so keep an eye out on your PPM levels at all times.

  • To rid your water of too many particles you can use things like a carbon filter or a reverse osmosis machine to clean your water. However, many growers agree that most tap water has helpful minerals (like calcium and magnesium) that actually help plants.
    • During and after the vegging stage, your plants will want more out of their feedings so filtering isn’t really necessary. That’s why we recommend only using filters at the beginning of the plant’s life when low PPM readings are needed
  • For a quick fix when PPM’s are high just add a bit of fresh water with a good pH level and watch them drop. Filtered, pH’ed water is great when things get a little too much in your reservoirs.
  • When readings are low it’s usually time to feed your plants. When you add nutrients to your feeding solution your PPM’s will go back up, and when your PPM’s and pH’s are in balance your plants are going to be happy and healthy.
    • Just remember that these readings need constant adjustment, so if you haven’t been keeping a close eye on your plant’s PPM and pH levels there’s no better time to start than now.
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31 thoughts on “pH and PPM: Knowing What Your Plants Are Eating and How Much They Can Handle”

    • That’s a great question, Jerry! The pH level of soil is around the same as hydroponic pH levels, but soil’s a little higher. When it comes to the pH balance of your plants, soil will need require slightly higher pH level than hydro. Hydroponics do not retain elements of nutrition like soil does, and soil can release elements to your plants at any time. For that reason, you’ll want to keep your levels at 5.8 to 6.5

  1. Very informative, i am beginner now and in a one month period i had lost 50% of my plants. now i will follow this article. Thanks and Regards

    • I’m really sorry to hear that. pH and PPM are readings that will tell you a lot about your plants, so if they’re off then you need to be sure to correct the problem right away. Get in to the habit of checking your water with a pH meter and a PPM meter and adjust your water accordingly. Remember, if your pH is off try using a pH buffer (like ph Up or pH Down) to correct the problem, and if your PPM’s are low make sure to add more nutrition in to your water.

  2. perfect read, thank you buddy some old fella like me needs new stuff like this. I have been doing this for many years and there is so much more to learn, i take delight in reading these posts.

    Best love,

  3. Hello,

    I was pretty impressed by this, it was a bit tricky at first but i got the hang of it. Who would of thought this much goes into feeding plants.

    • Hello Dee!

      We would love to answer that for you. If your PPM stays the same this means you would need to re-calibrate. Just to insure your plants are getting enough nutrients we would advise redoing over the steps that are listed. If is common for the PPM to stay the same so we would re calibrate our steps.

  4. Hi, I having problem my mixture ppm shoot up 300ppm after add in PH up.Do I need to add in water to get the right ppm or just don’t anything to the mixture. cause the PH UP didn’t contain nutrient like the fertilizer?

    • That’s a great question, Ken, because adjusting pH and PPM levels can get really tricky, especially if you use buffers like pH UP and DOWN.

      In short, yes, you can add water to your nutrient feeding solution to lower its PPM. However, there’s more to adjusting PPM than adding water to bring it back down.

      First, you’ll need to check the pH level of the water you’re using for PPM adjustment. There’s nothing worse than using pH buffers just for more water to throw them off, making you adjust the pH, leading to you adjusting the PPM again, and so on…

      Second, you’ll want to test the PPM of the water you want to fill. For the best results, we suggest using RO water to adjust PPM because RO water has no nutritional value. It may sound strange, but the lack of nutrients and minerals in RO water makes it the perfect base to adjust water levels: it won’t add anything dangerous and won’t directly cause nutrient spikes.

  5. How do you keep your ppms at the appropriate level during flower? I’ve been using plain PH water 4 times and then once with nutrients. Do I need to stop that and add nutrients when the ppms fall below 1000?

    • Good question, Jeremy. When it comes to PPM adjustment it all comes down to two ideas:

      1) When PPM levels are too low it’s a sign your plants don’t have as much food as they need to eat. In order to increase PPM you’ll want to add more nutrients into your feeding solution to reach optimum PPM (just make sure you also check the pH levels to assure that food isn’t harming your plants).
      2) When PPM levels are too high it’s a sign your plants have too much to eat, so you’ll want to dilute your solution with water. This will lower the PPM’s so that the concentration of nutrients is at a level that’s comfortable for your plants to digest.

      Keep in mind that PPM levels will fluctuate over the course of your plant’s life from seed to harvest, so keep an eye out on levels at all times and adjust accordingly.

  6. I have recently started using a ph and ppm meter for my first grow. Let me tell you this is way more helpful then the instructions that i was given. Loving this bruhh

  7. watch the soil out of the bag ph, then watch plants run-off ph
    you can compensate with the slightly higher or lower ph feeding
    just start watching your run-off water.

  8. Why the heck do nutrient companies (i.e. fox farm for example) list such high ppms in their charts. Everyone knows that’s too much right? Like they show up to 2000 ppms way sooner than you’d be even up to 1000 with this info… And thanks!

    • Hello There,

      Too high would range around 8.5 and Above it can cause serious harm and root damage to the plant. So you want to make sure you are measuring this out correctly.

  9. Thanks man. I have been growing for some 20 years. I had no problems with ph. I used well water same water over the years.So I got slack over the years in check my ph levels. well it came back to bite me in the ass. My plants were doing poorly over time little at a time. By the time I checked ph levels they were way to high 7.5. so I adjusted down. This was about a month ago. Things are looking better all the time. (Beatles). To all young growers out there check you ph save yourself a lot of trouble. Great article man. keep up the good work knowledge is power.

  10. First crop ….. my autoflower plants just started buddying and when I changed to bloom nutrients and put my water at 600 ppm with the nutrients my plants got nutrient burn . Why is your ppm levels so much higher than others I have read

    • I’m sorry to hear that, Steve. The first thing I should mention is that the readings suggested here are for full-grown plants. Because autoflowers will stay much shorter than regular plants, their nutrition doesn’t need to be as high. Also, you want to be sure to ease your plants into their feedings. For example, if the peak PPM for a plant says 600, you’ll want to start from your current PPM (for example sake, we’ll say 300 PPM) and slowly go up each feeding. If you go from 300 to 600 within a day it’ll shock your plants and unfortunately hurt them.

  11. I watered my plants with the ph around6.5 to 5.8. My question is I measure ppm before and after after adding up or down then measure ppm again and it changes which one do i go by before or after adding ph which do I go by for ppm.

    • Hello Dave,

      For the best result you would want to measure ppm after you add the PH. If you go by the before results they will not be accurate when adding the PH. We hope this information was a bit helpful for you, hit us up if you need any more assistance.

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